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Jovell, Megias Ferran. "Contact resistance and electrostatics of 2DFETs". Doctoral thesis, Universitat Autònoma de Barcelona, 2018. http://hdl.handle.net/10803/664041.
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Durant la darrera dècada, la popularització del grafè i altres materials de dues dimensions (2D) ha revolucionat
la ciència de materials. Els nous fenòmens físics que esdevenen en aquests nous materials obren les possibilitats
per a nous dispositius amb característiques extraordinàries. En el camp de l’electrònica d’alta freqüència,
per alguns d'aquests dispositius s'ha predit que poden obrir el forat que hi ha actualment en el rang del terahertz.
En aquesta tesis s'han fet servir diferents tècniques de simulació per estudiar diferents dispositius en l'entorn
d'alta freqüència en ment.
En primer lloc, un transistor d'efecte de camp compost per una mono capa de disulfit de molibdè (MoS$_2$) ha estat
estudiat fent servir el model de deriva difusió. Per aprofundir en això, s'ha estudiat també una unió $p-n$ amb
aquest mateix material. Malgrat que el model de deriva difusió està pensat per materials convencionals, s'ha fet
servir un conjunt de paràmetres efectius per tal de reproduir les dades experimentals. Amb aquest conjunt de paràmetres,
ha estat possible reproduir el corrent de sortida d'aquest transistor tot i que no el període de transició. D’altra banda,
els resultats de la unió $p-n$ han estat molt valuosos per a l'estudi de la zona de depleció.
Un dels obstacles a superar per poder poder utilitzar grafè i altres materials 2D en aplicacions d'alta freqüència, per tal
de no comprometre el rendiment d'aquests dispositius, és el d'obtenir una resistència de contact (R$_c$) prou baixa. En aquesta
tesi, s'ha proposat d'afegir una capa intermèdia de grafit entre el contacte metàl·lic i el canal de grafè per tal de reduir la
resistència de contacte per sota dels 100 $\Omega\cdot\mu$m que sovint es cita com el límit del qual pot limitar el rendiment dels
transistors d'efecte de camp. Un contacte de tipus ``top'' s'ha fet servir per a l'estructura de grafit-grafè que és molt convenient
per simulacions de transport balístic mitjançant la teoria de la densitat del funcional juntament amb la teoria del no equilibri
de green per a calcular aquesta resistència. En particular, s'han simulat diverses longituds de superposició del grafè sobre el
contacte de grafit per tal d'estudiar-ne el seu efecte. S'ha observat que per a concentracions de portadors intrínseques, la
resistència de contacte és molt alta, però per a làmines de grafè dopades, aquesta resistència decau per sota del límit citat.
Per tal d'avaluar aquests resultats, s'ha estudiat el camí de corrent mitjançant el formalisme d’autocanals. Aquesta anàlisi
demostra que la transferència d'electrons es duu a terme mitjançant l'àrea de solapament en comptes de la vora. El cas de vora
també ha estat considerat com a referència per ser el cas límit. S'ha conclòs que una capa de grafit abans de la capa de grafè
és viable per tal de reduir la resistència de contacte en els contactes metall-grafè.
Finalment, per tal d'entendre amb profunditat alguns dels resultats experimentals pel què fa a la resistència de contacte entre
un metall i el grafè, l'objectiu és de generar estructures realistes mitjançant la dinànima molecular. Per a tal fi, el primer
pas és el de parametritzar l'enllaç metall-carboni. El potencial d'odre d'enllaç fou escollit ja que és el potencial indicat per
descriure aquesta mena d'enllaços covalents. Les interaccions metall-metall foren descrites pel potencial d'àtom incrustat, i
la l'enllaç carboni-carboni pel potencial de Tersoff. El potencial de l'ordre d'enllaç està caracteritzat per un conjunt de deu
paràmetres que descriuen les característiques de l'enllaç com són la distància d'equilibri o l'energia d'enllaç, entre altres.
Mitjançant l'algorisme de Monte Carlo temperat paral·lel, s'ha pogut obtenir un conjunt de paràmetres per a la interacció Pd-C
i Ni-C.In the last decade, the rise of graphene and other 2-dimensional materials revolutionized materials science. The new physics brought by these new materials opened up the possibilities of new devices with outstanding characteristics. In the field of radiofrequency electronics, some of these devices are predicted to bridge the terahertz gap in the frequency spectrum. In this thesis, several simulation techniques have been employed to study different devices with this long term goal in mind. In first place, a single-layer molybdenum disulfide (MoS$_2$) field effect transistor (FET) has been studied using the drift-diffusion model. To delve deeper into this, a MoS$_2$ $p-n$ junction has also been studied in this framework. Even though the drift-diffusion model is suited for bulk materials, a set of effective parameters was found. With it, it has been possible to reproduce the on-current of experimental data of the single-layer MoS$_2$ FET, but not the subthreshold swing. On the other hand, the MoS$_2$ $p-n$ junction yielded valuable results for the study of the depletion region. One of the hurdles that must be overcome in order to harness the possibilities of graphene and other 2D materials so that the performance of high frequency devices is not compromised is to achieve a low enough contact resistance (R$_c$) between the metal contact and the channel. In this thesis, an intermediate graphite layer between the metal contact and the graphene layer is proposed in order to achieve the 100 $\Omega\cdot\mu$m mark that is often quoted to be the upper limit for $R_c$ not to be the limiting factor. A graphite-graphene top contact structure is proposed and studied under ballistic transport by density functional theory (DFT) and Non-Equilibrium Green's Function Theory (NEGF) to calculate the contact resistance. In particular, several overlap amounts between graphene over the graphite bulk were studied. The results obtained are very promising for doped samples of graphene. To assess these results, a current path analysis was conducted using the eigenchannel formalism. This analysis showed that the transfer of electrons was done through the area of contact instead of an edge. It was concluded that graphite was a suitable buffer to reduce R$_c$ for metal-graphene contacts. Finally, in order to understand better some of the experimental results in the contact resistance of metal-graphene contacts, the objective was to generate realistic atomic configurations using Molecular Dynamics. For that, a first step is to parametrize the metal-carbon interactions. The bond order potential (BOP) force field was chosen for this as it is a force field that can accurately describe the metal-carbon covalent bond. The metal-metal bond is described using the embeded atom potential (EAM) and the carbon-carbon interaction, by the Tersoff force field. The BOP force field has a ten parameter set that describe the characteristics of the bond: equilibirum distance, bond energy, etc. Using Parallel Tempering Monte Carlo (PTMC) optimisation algorithm trained from first principles calculations of small metal particles on top of a graphene sheet, a set of parameters for the BOP force field was obtained for the Pd-C and Ni-C pairs.
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Gibbins, Josh. "Thermal Contact Resistance of Polymer Interfaces". Thesis, University of Waterloo, 2006. http://hdl.handle.net/10012/2856.
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In this study an experimental program was carried out to determine the thermal contact resistance at polymer interfaces. Specifically, a polycarbonate to stainless steel interface along with a polycarbonate to polycarbonate interface were investigated. The thermal contact resistance at a stainless steel to stainless steel interface was also investigated for comparison purposes. Experimental data was obtained over a pressure range of approximately 600 - 7000 kPa, in a vacuum environment. The experimental data was compared to the CMY plastic contact model, the Mikic elastic contact model and the SY elasto-plastic contact model to investigate the ability of such established thermal contact models to predict the thermal contact resistance at polymer interfaces. Based upon predictions made in regards to the mode of deformation of the asperities on the contacting surfaces the appropriate contact model showed good agreement with the experimental data for the stainless steel-stainless steel data set and the polycarbonate-stainless steel data sets. There was poor agreement between the all three contact models and the experimental data for the polycarbonate-polycarbonate data sets. It was determined that uncertainties in the proposed experimental method prevented an accurate measurement of the thermal contact resistance values for the polycarbonate-polycarbonate data sets.
The purpose of this investigation was to extend the use of established thermal contact models to polymer interfaces and to provide a comparison between the thermal contact resistance values of metal and polymer interfaces.
Thermal contact resistance for the polymer to metal interface was shown to be predicted by the Mikic elastic contact model in comparison to the metal to metal interface which was shown to be predicted by the CMY plastic contact model. The thermal contact resistance for a polymer interface was found to be on the same order as a metal interface.
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Almeida, Lia Ramadoss Ramesh. "Experimental and theoretical investigation of contact resistance and reliability of lateral contact type ohmic MEMS relays". Auburn, Ala., 2006. http://repo.lib.auburn.edu/2006%20Fall/Theses/ALMEIDA_LIA_13.pdf.
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Reshamwala, Chetak M. (Chetak Mahesh) 1979. "Contact resistance in RFID chip-antenna interfaces". Thesis, Massachusetts Institute of Technology, 2001. http://hdl.handle.net/1721.1/8193.
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Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2001.Includes bibliographical references (p. 21).
The purpose of this study was to determine a force-deflection relationship and a force-contact area relationship between a flat planar solid and a spherical solid in terms of material and surface properties of the two bodies. This relationship was determined and it was discovered that the force was directly proportional to both the deflection and contact area. This information is useful in the design and performance of RFID chips. The RFID chip-antenna interface is the area of greatest power loss in the system, and by determining a relationship to increase the contact area in that region, the power loss to the antenna can be reduced. Moreover, an analysis including asperities on the micro scale geometry of the solids was conducted. In the final approach to the problem, a random distribution of asperity types was analyzed. An expression was derived for the total force applied in terms of a given deflection and a range of asperity radii of curvature. A three-dimensional graph was created to show how each of these variables depends on the each other when asperities exist. This relationship is very significant, because it can be used to improve current RFID chip technology to achieve better performance. This expression can also be used to determine specifications in the manufacturing process to achieve a certain deflection or area of contact between the contacting bodies, thereby improving the current manufacturing process.
by Chetak M. Reshamwala.
S.B.
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Wilson, W. Everett Jackson Robert L. "Surface separation and contact resistance considering sinusoidal elastic-plastic multiscale rough surface contact". Auburn, Ala, 2008. http://hdl.handle.net/10415/1490.
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Gill, Jennifer. "AN INVERSE ALGORITHM TO ESTIMATE THERMAL CONTACT RESISTANCE". Master's thesis, University of Central Florida, 2005. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/2546.
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Thermal systems often feature composite regions that are mechanically mated. In general, there exists a significant temperature drop across the interface between such regions which may be composed of similar or different materials. The parameter characterizing this temperature drop is the thermal contact resistance, which is defined as the ratio of the temperature drop to the heat flux normal to the interface. The thermal contact resistance is due to roughness effects between mating surfaces which cause certain regions of the mating surfaces to loose contact thereby creating gaps. In these gap regions, the principal modes of heat transfer are conduction across the contacting regions of the interface, conduction or natural convection in the fluid filling the gap regions of the interface, and radiation across the gap surfaces. Moreover, the contact resistance is a function of contact pressure as this can significantly alter the topology of the contact region. The thermal contact resistance is a phenomenologically complex function and can significantly alter prediction of thermal models of complex multi-component structures. Accurate estimates of thermal contact resistances are important in engineering calculations and find application in thermal analysis ranging from relatively simple layered and composite materials to more complex biomaterials. There have been many studies devoted to the theoretical predictions of thermal contact resistance and although general theories have been somewhat successful in predicting thermal contact resistances, most reliable results have been obtained experimentally. This is due to the fact that the nature of thermal contact resistance is quite complex and depends on many parameters including types of mating materials, surface characteristics of the interfacial region such as roughness and hardness, and contact pressure distribution. In experiments, temperatures are measured at a certain number of locations, usually close to the contact surface, and these measurements are used as inputs to a parameter estimation procedure to arrive at the sought-after thermal contact resistance. Most studies seek a single value for the contact resistance, while the resistance may in fact also vary spatially. In this thesis, an inverse problem (IP) is formulated to estimate the spatial variation of the thermal contact resistance along an interface in a two-dimensional configuration. Temperatures measured at discrete locations using embedded sensors appropriately placed in proximity to the interface provide the additional information required to solve the inverse problem. A superposition method serves to determine sensitivity coefficients and provides guidance in the location of the measuring points. Temperature measurements are then used to define a regularized quadratic functional that is minimized to yield the contact resistance between the two mating surfaces. A boundary element method analysis (BEM) provides the temperature field under current estimates of the contact resistance in the solution of the inverse problem when the geometry of interest is not regular, while an analytical solution can be used for regular geometries. Minimization of the IP functional is carried out by the Levenberg-Marquadt method or by a Genetic Algorithm depending on the problem under consideration. The L-curve method of Hansen is used to choose the optimal regularization parameter. A series of numerical examples are provided to demonstrate and validate the approach.M.S.
Department of Mechanical, Materials and Aerospace Engineering;
Engineering and Computer Science
Mechanical Engineering
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Taphouse, John Harold. "Thermal contact resistance in carbon nanotube forest interfaces". Diss., Georgia Institute of Technology, 2015. http://hdl.handle.net/1853/54853.
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The continued miniaturization and proliferation of electronics is met with significant thermal management challenges. Decreased size, increased power densities, and diverse operating environments challenge the limitations of conventional thermal management schemes and materials. To enable the continuation of these trends thermal interface materials (TIMs) that are used to enhance heat conduction and provide stress relief between adjacent layers in a electronic package must be improved. Forests comprised of nominally vertically aligned carbon nanotubes (CNTs), having outstanding thermal and mechanical properties, are excellent candidates for next-generation thermal interface materials (TIMs). However, despite nearly a decade of research, TIMs based on vertically aligned CNT forests have yet to harness effectively the high thermal conductivity of individual CNTs. One of the key obstacles that has limited the performance of CNT TIMs is the presence of high thermal contact resistances between the CNT free ends and the surfaces comprising the interface. The aim of this research is to better understand the mechanisms by which the thermal contact resistance of CNT forest thermal interfaces can be reduced and to use this understanding towards the design of effective and to scalable processing methods. Contact area and weak bonding between the CNT tips and opposing surface are identified as factors that contribute significantly to the thermal contact resistance. Three strategies are explored that utilize these mechanisms as instruments for reducing the contact resistance; i) liquid softening, ii) bonding with surface modifiers, and iii) bonding with nanoscale polymer coatings. All three strategies are found to reduce the thermal contact resistance at the CNT forest tips to below 1 mm2-K/W, a value to where it is no longer the factor limiting heat conduction in CNT forest TIMs. These strategies are also relatively low-cost and amenable to scaling for production when compared to existing metal-based bonding strategies.
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Yang, Yulin. "Evaluation of rolling contact fatigue resistance for coated components". Thesis, University of Hull, 2003. http://hydra.hull.ac.uk/resources/hull:8534.
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The thesis reviews and studies current evaluation mechanisms, techniques and machines for testing rolling contact fatigue failure resistance and load capacity of coated components. The thesis investigates both normal and accelerated rolling contact fatigue evaluation test mechanisms and their models, and evaluation test technique principles suitable to the appraisal of coated bearing components. A major contribution of the thesis is the design and development of a new rolling contact fatigue evaluation test machine for coated components. Tests of the rolling contact fatigue of coated bearing raceways under the oil lubricant, grease lubricant and no lubricant conditions, applying the new rolling contact fatigue evaluation mechanisms, evaluation technique principles and the new test machine, have been performed. The accelerated rolling contact fatigue tests of the coated bearing raceways use SiC powder in the oil lubricant. The new rolling contact fatigue test machine has been found suitable for evaluating the rolling contact fatigue resistance of components with superhard coatings. The accelerated rolling contact fatigue test method has been shown to give comparable rolling contact fatigue test results to those obtained in a normal rolling contact fatigue test, while being much faster. In the fatigue test, the cyclic maximum shear stress produces an initial fatigue crack near the substrate surface of the test bearing raceways. The observed phenomena are consistent with theory, although the location of the initial crack is much closer to the surface than would be predicted by a 'static' Hertzian analysis. Insufficient traction forces on the contact surface between the rolling elements of a test coated bearing makes gross skidding occur, leading to rapid wear, over-heating and final failure of the test coated bearing. The LSO fatigue life of the test coated bearing raceway tends to decrease with increase of the coating thickness and coating hardness of the test coated bearing raceway.
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Sun, Ta-chien. "Fundamental study of contact resistance behavior in RSW aluminum". Connect to this title online, 2003. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1069807481.
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Thesis (Ph. D.)--Ohio State University, 2003.Title from first page of PDF file. Document formatted into pages; contains xxviii, 314 p.; also includes graphics (some col.) Includes bibliographical references (p. 303-314). Available online via OhioLINK's ETD Center
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Li, Wei 1967. "Determination of the relationship between thermal contact resistance and contact pressure based on their distributions". Thesis, McGill University, 1994. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=26402.
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Loading conditions in a machine structure usually cause the contact pressure at the joints to take the form of a distribution, which in turn causes thermal contact resistance to be position-dependent also.In the experiments described in this thesis, two thin-plate specimens of steel under plane-stress loading conditions generating contact pressure distributions of various profiles at the interface, were subjected to a thermal field. Temperature measurements served as reference for the finite element modelling which, through consecutive iterations, provided the values for the thermal contact resistance distributions. Combined mechanical contact pressure and thermal contact stress distributions were considered at the interface.
The function representing the relationship between thermal contact resistance and contact pressure for various distributions was defined using the least squares method. It was revealed that although this relationship can be expressed by the single function for the whole experimental range, the deviations experienced for different slopes and forms of distributions (convex and concave), particularly noticeable for steep slopes at high contact pressure levels, could indicate the effect of macro-constriction resistance, however small its values according to the theoretical calculations might be.
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Hong, Fangjun. "Droplet spreading, substrate remelting and variable thermal contact resistance in microcasting /". View abstract or full-text, 2005. http://library.ust.hk/cgi/db/thesis.pl?MECH%202005%20HONG.
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Frolish, Michael Fraser. "Design criteria for rolling contact fatigue resistance in back-up rolls". Thesis, University of Sheffield, 2002. http://etheses.whiterose.ac.uk/15083/.
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The demands placed on back-up rolls in hot strip mills have been investigated by a combination of literature and industrial studies. The tribological operating conditions have been established and the maximum local loads and pressure distributions at the work roll/back-up roll interface have been obtained by processing mill and roll schedule data using a computer program (commercial software developed by V AI Industries (UK) Ltd) and applying the theories of contact mechanics. After a study of the responses of the rolls to these demands and possible failure mechanisms, research has centred on surface initiated damage whereby cracks can propagate into the roll substrate potentially reaching the internal residual stress fields and leading to catastrophic failure. A proposed qualitative contact and fracture mechanics model, for the rolling contact fatigue and spalling failure, has been quantified theoretically using published methods for determining the stress intensity factors at the tips of pressurised and water lubricated, inclined rolling contact fatigue cracks. The predictions of the quantitative model in terms of crack directions and lengths have been validated by microscopic observation of the morphologies cracks produced in test discs used in the "SUROS" Rolling-Sliding Testing Machine and also in a sample of material spalled from a back-up roll. The quantitative failure model includes criteria for crack branching either upwards leading to micro spalling or downwards (potentially catastrophic) and the link between these two cases has been related quantitatively to the value of the mode I threshold for the roll material. After linking mechanics to microstructure and quantifying the interactions between wear and rolling contact fatigue in this case, practical quantitative recommendations have been made for the design of bainitic back-up roll materials, back-up roll redressing procedures and the surface roughness of both the work rolls and back-up rolls presented to the mill.
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Tanguturi, Sai Kishan. "Effect on Contact Resistance dueto Cross Connection of MC4 Compatible Connector". Thesis, Högskolan Dalarna, Energiteknik, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:du-28838.
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Electrical connectors are the blocks that connect solar panels together. Whenever a photovoltaic plant commences, the main discussion goes around on solar panels, inverters, charge controllers, etc. But the topic of connectors is usually hardly discussed. Connectors in a photovoltaic system can definitely contribute to improve the overall performance of the system, provided that importance is given while selecting the connectors. The electrical connectors used in photovoltaic systems can be connected in two possible ways. Connectors can be connected either in a pure-connection or in a cross-connection. Male and female connectors from the same brand results a pure-connection (P-C). Male and female connectors from two different brands results in a cross-connection (C-C). There have been discussions in photovoltaic, electrical connector markets and international solar events regarding the risks involved, losses and consequences due to a cross-connection. The main reason behind cross-connections is the unawareness of the installers in knowing the difference between a pure-connection and a cross-connection. Even though the installers are aware of this difference, they are not aware of the consequences of cross-connections. Multi-Contact, a leading electrical connector manufacturer of MC4 photovoltaic connectors affected by the counterfeit products of MC4, due to the sudden boom in the solar market during 2011-12. With the help of TÜV Rheinland, Multi-Contact conducted couple of tests namely temperature increase test and accelerated stress tests to understand the disadvantages of cross-connections. This thesis tried to replicate the tests performed by Multi-Contact in an attempt to understand the test results by using connectors that are used in the Swedish market. Performing temperature increase test and accelerated stress tests on most commonly used connectors in the Swedish market is the main aim of this thesis. The first test, gives an understanding of the temperature variations across various connector sets (four connector sets from various manufacturers used in this thesis) and the latter tests helps to understand the quality of the contact resistance of these connector sets. The four connector set manufacturers used in this test were Multi-Contact (MC), Weidmüller (WM), Blussun solar (BSS) and PBM. The quality of contact resistance of a connector is directly related to the quality of the connector set. During the 20 minutes of the temperature increase test, the connector set from WM performed better than its competitors in the P-C. Whereas, the MC-BSS connector set had performed well in the C-C. The connector type of male MC and female BSS showed its dominance throughout the test. Unfortunately, no conclusions were able to be drawn from this test results due to insufficient information about the test procedure. From the results of accelerated stress tests, the C-C set from MC outperformed its P-C counterpart. All ten connector sets used in this project passed the standard and qualified as connectors with good quality contact resistance. Therefore the best results out of only a P-C connector set does not seems to be completely true. With the standard used in this thesis, it is quite difficult to judge the quality of connectors. Rather than saying a P-C is superior and a C-C is inferior in terms of quality, there is a need to come up with a new method to evaluate the quality of connectors. Matching the connectors based on their tolerances could be a potential solution to the mismatching problem in connectors.
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Eby, Anne Kathryn. "Factors affecting medical-surgical area nurses' compliance with contact precautions". Thesis, Montana State University, 2009. http://etd.lib.montana.edu/etd/2009/eby/EbyA1209.pdf.
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Multidrug-resistant organisms are a significant threat in health care facilities, and are associated with many adverse consequences for infected patients. However, despite these concerns and the evidence that contact precautions are an effective way to address them, compliance with contact precautions guidelines among health care workers remains low (Farr, 2000). The primary goal of this study was to examine factors affecting medical-surgical nurses' compliance with contact precautions guidelines when caring for patients colonized by or infected with multidrug-resistant organisms. A secondary purpose of this study was to describe demographic characteristics of medical-surgical nurses to determine if certain characteristics (e.g. age, time in practice, level of education) had a relationship with their compliance in using contact precautions guidelines. Finally, this study examined barriers to the use of contact precautions and consequences for failure to follow contact precautions guidelines. A survey tool was developed by the researcher for this study to examine these questions, and an exploratory, cross-sectional, correlation descriptive study was conducted. The study group was made up primarily of female nurses with associate or bachelor degrees. Nurses from the orthopedic and neurosurgery unit made up the largest percentage of respondents. All respondents indicated that they were familiar with CP guidelines. Eight primary barriers to the use of contact precautions were listed by participants. Half of the participants listed one of the time management categories ("no time" or "urgency") as the primary barrier to compliance with contact precautions. Participants' age, years experience and level of education were not statistically significant predictors of the participants' level of compliance. There was not a statistically significant difference between the barriers to compliance groups (no time/urgency versus other) on their ability to comply with contact precautions. Lastly, there was not a statistically significant relationship among the primary consequence of non-compliance with CP guidelines (medical versus other) and the participants' level of compliance (low versus high).
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Shi, Lei Photovoltaics & Renewable Energy Engineering Faculty of Engineering UNSW. "Contact resistance study on polycrystalline silicon thin-film solar cells on glass". Publisher:University of New South Wales. Photovoltaics & Renewable Energy Engineering, 2008. http://handle.unsw.edu.au/1959.4/41425.
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Thin-film solar cells are widely recognised to have the potential to compete with fossil fuels in the electricity market due to their low cost per peak Watt. The Thin-Film Group at the University of New South Wales (UNSW) is engaged in developing polycrystalline silicon (poly-Si) thin-film solar cells on glass using e-beam evaporation technology. We believe our solar cells have the potential of significantly lowering the manufacturing cost compared to conventional, PECVD-fabricated thin-film solar cells. After years of materials research, the focus of the Group??s work is now moving to the metallisation of evaporated solar cells. Minimising various kinds of losses is the main challenge of the cell metallisation procedure, within which the contact resistance is always a big issue. In this thesis, the contact resistance of aluminium contacts on poly-Si thin-film solar cells on glass is investigated. To the best of the author??s knowledge, this is the first ever contact resistance investigation of Al contacts on evaporated poly-Si material for photovoltaic applications. Various transmission line models (TLM) are employed to measure the contact resistance. An improved TLM model is developed to increase the measurement precision and, simultaneously, to simplify the TLM pattern fabrication process. In order to accommodate the particular requirements of poly-Si coated glass substrates, a TLM pattern fabrication process using photolithography is established. Furthermore, a Kelvin sense tester is set up to ensure an accurate measurement of the contact resistance. After establishment of the TLM technique at UNSW, it is successfully tested on singlecrystalline silicon wafer samples. The thermal annealing process of the contacts is also optimised. Then, the general behaviour of Al contacts on uniformly doped poly-Si films (i.e., no p-n junction) is investigated using the verified TLM technique. The long-term stability of the contacts is also studied. This is followed by an investigation of the contact resistance of the back surface field and emitter layers of different types of poly-Si thin-film solar cells. Finally, a novel contact resistance measurement model is proposed that is believed to be able to overcome the measurement bottleneck of the transmission line models.
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Bahrami, Majid. "Modeling of Thermal Joint Resistance for Sphere-Flat Contacts in a Vacuum". Thesis, University of Waterloo, 2004. http://hdl.handle.net/10012/876.
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As a result of manufacturing processes, real surfaces have roughness and surface curvature. The real contact occurs only over microscopic contacts, which are typically only a few percent of the apparent contact area. Because of the surface curvature of contacting bodies, the macrocontact area is formed, the area where microcontacts are distributed randomly. The heat flow must pass through the macrocontact and then microcontacts to transfer from one body to another. This phenomenon leads to a relatively high temperature drop across the interface. Thermal contact resistance (TCR) is a complex interdisciplinary problem, which includes geometrical, mechanical, and thermal analyses. Each part includes a micro and a macro scale sub-problem. Analytical, experimental, and numerical models have been developed to predict TCR since the 1930's. Through comparison with more than 400 experimental data points, it is shown that the existing models are applicable only to the limiting cases and none of them covers the general non-conforming rough contact. The objective of this study is to develop a compact analytical model for predicting TCR for the entire range of non-conforming contacts, i. e. , from conforming rough to smooth sphere-flat in a vacuum. The contact mechanics of the joint must be known prior to solving the thermal problem. A new mechanical model is developed for spherical rough contacts. The deformation modes of the surface asperities and the bulk material of contacting bodies are assumed to be plastic and elastic, respectively. A closed set of governing relationships is derived. An algorithm and a computer code are developed to solve the relationships numerically. Applying Buckingham Pi theorem, the independent non-dimensional parameters that describe the contact problem are specified. A general pressure distribution is proposed that covers the entire spherical rough contacts, including the Hertzian smooth contact. Simple correlations are proposed for the general pressure distribution and the radius of the macrocontact area, as functions of the non-dimensional parameters. These correlations are compared with experimental data collected by others and good agreement is observed. Also a criterion is proposed to identify the flat surface, where the influence of surface curvature on the contact pressure is negligible. Thermal contact resistance is considered as the superposition of macro and micro thermal components. The flux tube geometry is chosen as the basic element in the thermal analysis of microcontacts. Simple expressions for determining TCR of non-conforming rough joints are derived which cover the entire range of TCR by using the general pressure distribution and the flux tube solution. A complete parametric study is performed; it is seen that there is a value of surface roughness that minimizes TCR. The thermal model is verified with more than 600 data points, collected by many researchers during the last 40 years, and good agreement is observed. A new approach is taken to study the thermal joint resistance. A novel model is developed for predicting the TCR of conforming rough contacts employing scale analysis methods. It is shown that the microcontacts can be modeled as heat sources on a half-space for engineering applications. The scale analysis model is extended to predict TCR over the entire range of non-conforming rough contacts by using the general pressure distribution developed in the mechanical model. It is shown that the surface curvature and contact pressure distribution have no effect on the effective micro thermal resistance. A new non-dimensional parameter is introduced as a criterion to identify the three regions of TCR, i. e. , the conforming rough, the smooth spherical, and the transition regions. An experimental program is designed and data points are collected for spherical rough contacts in a vacuum. The radius of curvature of the tested specimens are relatively large (in the order of m) and can not be seen by the naked eye. However, even at relatively large applied loads the measured joint resistance (the macro thermal component) is still large which shows the importance of surface out-of-flatness/curvature. Collected data are compared with the scale analysis model and excellent agreement is observed. The maximum relative difference between the model and the collected data is 6. 8 percent and the relative RMS difference is approximately 4 percent. Additionally, the proposed scale analysis model is compared/verified with more than 880 TCR data points collected by many researchers. These data cover a wide range of materials, surface characteristics, thermal and mechanical properties, mean joint temperature, directional heat transfer effect, and contact between dissimilar metals. The RMS difference between the model and all data is less than 13. 8 percent.
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Thompson, Mary Kathryn 1980. "A multi-scale iterative approach for finite element modeling of thermal contact resistance". Thesis, Massachusetts Institute of Technology, 2007. http://hdl.handle.net/1721.1/42069.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2007.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Includes bibliographical references.
Surface topography has long been considered a key factor in the performance of many contact applications including thermal contact resistance. However, essentially all analytical and numerical models of thermal contact resistance and thermal contact conductance either neglect surface topography or make simplifications and assumptions about the nature of the surface. This work combines measured surface geometry with an iterative thermal/structural finite element model to more accurately predict microscopic and macroscopic thermal contact resistance. A commercial power electronics module which exhibits both macroscopic surface form and micro scale surface roughness is analyzed using three different macro scale surface models to verify the accuracy of the model and to demonstrate the impact of geometric surface assumptions. Finally, the factors influencing the thermal/structural behavior of bolted plates are examined and recommendations for reducing both contact resistance and the overall thermal resistance of bolted plate systems are presented.
by Mary Kathryn Thompson.
Ph.D.
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Locker, Graham J. "Fretting corrosion of tin-plated separable connectors used in automotive applications". Thesis, Loughborough University, 1998. https://dspace.lboro.ac.uk/2134/32165.
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Greater demands are being placed on the separable connector to perform with higher reliability in harsher automotive environments. Corrosion in its various forms is a major mechanism which affects contact reliability and this current work focuses on surface oxidation and the related phenomenon of fretting corrosion, from which hot dipped tin (HDT), a common automotive connector coating, is known to suffer. For an in-depth study of high contact resistance, in both static conditions and when subjected to relative micromovement, an interdisciplinary approach was necessary, drawing on the results of published work carried out in the fields of contact and surface science, corrosion and tribology.
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Yang, Jing 1988. "Grinding effects on surface integrity, flexural strength and contact damage resistance of coated hardmetals". Doctoral thesis, Universitat Politècnica de Catalunya, 2016. http://hdl.handle.net/10803/396135.
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This thesis assesses the influence of substrate surface integrity on different mechanical (flexural strength and contact damage resistance under spherical indentation) and tribological (scratch resistance as well as cracking and delamination response under Brale indentation) properties for a TiN-coated fine-grained hardmetal grade (WC-13 wt.%Co). In doing so, three different surface finish conditions are studied: as-sintered (AS), ground (G), mirror-like polished (P) and ground plus thermal annealed (GTT). Moreover, a relevant part of the work is devoted to nude hardmetal substrates.
The result indicates that grinding induces significant alterations in the surface integrity. It yielded in high roughness and emergence of a topographic texture; anisotropic distribution of microcracks within a thin subsurface layer; severe deformation, microstructure refinement and phase transformation of binder regions; and large compressive residual stresses. Subsequent ion etching and coating deposition resulted in a significant residual stresses decrease while damage induced by grinding was not completely removed in the substrate surface. On the other hand, high temperature annealing (GTT condition) completely relieved the referred residual stresses, but without inducing any additional change in terms of existing damage. This was not the case for the metallic binder phase where such treatment induced an unexpected microporosity, development of a recrystallized subgrain structure and reversion of grinding-induced phase transformation.
Strength of hardmetals was significantly enhanced by grinding, as compared to AS and P conditions. Such beneficial effect is partly lost during the subsequent ion etching and coating deposition stages. On the other hand, strength of coated GTT condition increases compared to that of the corresponding uncoated one. Systematic residual stress analysis combined with extensive fractographic inspection reveal that strength variations measured after individual manufacturing chain or heat treatment steps (grinding, ion-etching, coating and/or thermal annealing) may be rationalized on the basis of effective residual stress state and location, either at the surface or at the subsurface, of strength-controlling flaws.
Independent of substrate surface finish, coated AS, G and P samples exhibit similar critical load for initial substrate exposure as well as same predominant failure mode as they get scratched. However, clear differences in the failure scenario were evidenced. Scratch track for G samples exhibited discrete and localized substrate exposure, compared to the more pronounced and continuous exposure for AS and P ones. On the other hand, GTT samples showed lower critical load and changes in the mechanisms for the scratch-related failure; the latter depending on the relative orientation between scratch and grinding directions.
Coated hardmetals exhibit more brittleness and lower adhesion strength, under Brale indentation testing conditions, with decreasing binder content. Grinding is discerned to promote delamination, compared to the polished condition, but also to strongly inhibit radial cracking. Such a response is analyzed on the basis of the interaction between elastic-plastic deformation imposed during indentation and several grinding-induced effects: remnant compressive stress field, pronounced surface texture and microcracking within a thin microcracked subsurface layer.
Contact damage resistance of coated hardmetals, subjected to spherical indentation, is enhanced by grinding of the substrate previous to coating stage. Such beneficial effects are discerned regarding both crack nucleation at the coating surface and subsequent propagation into the hardmetal substrate. The grinding-induced compressive residual stresses are pointed out as the main reason for the improved response against contact loading. Such statement is sustained by the lower damage resistance evidenced in coated GTT specimens.En este trabajo se estudia la influencia de la integridad superficial del sustrato sobre diferentes propiedades mecánicas (resistencia tanto a la rotura en flexión como al daño inducido por contacto) y tribológicas (resistencia al rayado así como el comportamiento bajo solicitaciones de indentación Brale) de una calidad fina de metal duro (WC-13% peso Co) recubierta con una capa de TiN. La investigación incluye la consideración de cuatro acabados superficiales: en condiciones de sinterizado (AS), rectificado (G), pulido (P), y rectificado más un tratamiento térmico de recocido (GTT). Los resultados indican que el rectificado induce alteraciones importantes en la integridad superficial: se incrementa la rugosidad y emerge una textura superficial; se evidencia la existencia de microfisuras, anisotrópicamente distribuidas a nivel subsuperficial; se introduce una deformación muy severa, lo cual da lugar a un refinamiento de la microestructura y transformación de fase en el ligante metálico; y finalmente, se inducen tensiones residuales compresivas elevadas. Estas tensiones se ven reducidas durante las etapas subsecuentes de pulverización por bombardeo iónico y deposición de la capa cerámica. Por su parte, las tensiones residuales referidas si son completamente eliminadas en las muestras GTT, aunque sin que el tratamiento posterior al rectificado induzca cambio alguno respecto al daño existente. Éste no es el caso para la fase metálica, donde el tratamiento de recocido conlleva la aparición de una inesperada microporosidad, recristalización microestructural a nivel subsuperficial y la reversión de la transformación de fase inducida durante el rectificado. La operación de rectificado resultó en un incremento significativo de la resistencia a flexión del metal duro. Este efecto positivo se perdió parcialmente al recubrir el material. Por el contrario, la deposición de la capa de TiN promovió un aumento de la resistencia mecánica para la condición GTT. Las variaciones en resistencia a rotura determinadas se explican considerando las tensiones residuales efectivas existentes en cada caso y la ubicación, en la superficie o por debajo de ella, de los defectos críticos responsables de la rotura del material. La carga crítica para la exposición del sustrato en el ensayo de rayado resultó ser Independiente del acabado superficial, para las muestras AS, G y P. Sn embargo, el daño irreversible inducido por el indentador bajo condiciones de contacto y deslizamiento simultáneo fue discreto y localizado para las muestras G, a diferencia de la exposición continua y más pronunciada del sustrato que se evidenció en las condiciones AS y P. Por su parte, las muestras GTT mostraron una carga crítica inferior y cambios relevantes en el mecanismo de fallo correspondiente. El ensayo de indentación Brale de metales duros recubiertos indicó una mayor fragilidad y una menor resistencia a la adhesión para la calidad con menor contenido de ligante metálico. En este marco experimental, y en comparación con el acabado de pulido, se evidenció que el rectificado del sustrato favorece la delaminación, pero también inhibe la aparición de fisuras radiales en metales duros recubiertos. La respuesta observada se analiza y explica sobre las bases de la interacción entre la deformación elasto-plástica impuesta durante la indentación y las alteraciones en integridad superficial resultantes del rectificado. El rectificado del sustrato, previo a la deposición de una capa cerámica, incrementa la resistencia al daño inducido bajo solicitaciones de contacto esférico. Esta influencia positiva se evidencia en términos no solo de la nucleación de fisuras sino también de la subsecuente propagación de ellas dentro del sustrato de metal duro. La principal razón de ello son las elevadas tensiones residuales de compresión introducidas en el proceso de rectificado. Esta afirmación se sustenta por la menor resistencia al daño por contacto que se determinó en las muestras GTT recubierta
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Marinkovic, Marko [Verfasser]. "Contact resistance effects in thin film solar cells and thin film transistors / Marko Marinkovic". Bremen : IRC-Library, Information Resource Center der Jacobs University Bremen, 2013. http://d-nb.info/1037014243/34.
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Yang, Jing. "Grinding effects on surface integrity, flexural strength and contact damage resistance of coated hardmetals". Doctoral thesis, Linköpings universitet, Nanostrukturerade material, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-127341.
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The tribological and mechanical behavior of coated tools depends not only on intrinsic properties of the deposited film but also on substrate surface and subsurface properties – such as topography and residual stress state – as well as on interface adhesion strength. It is particularly true in the case of coated tools based on WC-Co cemented carbides (backbone materials of the tool manufacturing industry, and simply referred to as hardmetals in practice) as substrates. Manufacturing of hardmetals often involves grinding, and in the case of cutting tools also edge preparation, etching and coating. The quality of the shaped components is influenced by how the surface integrity evolves through the different process steps. In this regard, substrate grinding and coating deposition represent key steps, as they are critical for defining the final performance and relative tool manufacturing cost. Within this framework, it is the main objective of this thesis to assess the influence of substrate surface integrity on different mechanical (flexural strength and contact damage resistance under spherical indentation) and tribological (scratch resistance as well as cracking and delamination response under Brale indentation) properties for a TiN-coated fine-grained hardmetal grade (WC-13 wt.%Co). In doing so, three different surface finish conditions are studied: as-sintered (AS), ground (G), and mirror-like polished (P). Moreover, aiming for an in-depth analysis of surface integrity evolution from grinding to coating, a relevant part of the work is devoted to document and understand changes induced by grinding in nude hardmetal substrates. The study is also extended to a fourth surface finish variant (GTT), corresponding to a ground substrate which is thermal annealed before being ion etched and coated. Because residual stress induced by grinding are effectively relieved after this high temperature thermal treatment, GTT condition allows to separate grinding-induced effects associated with surface texture and surface/subsurface damage changes (inherited from the G surface finish) from those related to the referred residual stresses. Surface integrity was characterized in terms of roughness, residual stresses (prior and after coating deposition), and damage at the subsurface level. It was found that grinding induces significant alterations in the surface integrity of cemented carbides. Main changes included relevant roughness variations; emergence of a topographic texture; anisotropic distribution of microcracks within a subsurface layer of about 1 micron in depth; severe deformation, microstructure refinement and phase transformation of binder regions, down to 5 microns in depth; and large compressive residual stresses, gradually decreasing from the surface to baseline values at depths of about 10-12 microns. Additional changes in surface integrity are induced during subsequent ion etching and coating deposition. In general, removal of material from the surface during sputter cleaning and extended low-temperature (during film deposition) treatment resulted in a significant residual stresses decrease (about half its original value). However, damage induced by grinding was not completely removed, and some microcracks were still left on the substrate surface (close to the interface). On the other hand, and as expected, high temperature annealing (GTT condition) resulted in a complete relief of the referred residual stresses, but without inducing any additional change in terms of existing microcracks and depth of damaged layer. This was not the case for the metallic binder phase where thermal treatment induced an unexpected microporosity, development of a recrystallized subgrain structure, and reversion of grinding-induced phase transformation. Flexural strength was measured on both uncoated and coated hardmetals, and complemented with extensive fractographic analysis. It was found that grinding significantly enhances the strength of hardmetals, as compared to AS and P conditions. However, such beneficial effect was partly lost in the corresponding coated specimens. On the other hand, film deposition increases strength measured for GTT surface variant. These findings were analyzed on the basis of the changes on nature and location of critical flaws, induced by the effective residual stress field resulting at the surface and subsurface after each manufacturing stage. The influence of substrate surface finish on scratch resistance of coated hardmetals and associated failure mechanisms was investigated. It was found that coated AS, G and P samples exhibit similar critical load for initial substrate exposure and the same brittle adhesive failure mode. However, damage scenario was discerned to be different. Substrate exposure was discrete and localized to the scratch tracks for G samples, while a more pronounced and continuous decohesion was seen for AS and P ones. Relieving of the substrate compressive residual stresses (GTT condition) yielded lower critical loads and changes in the mechanisms for the scratch-related failure, the latter depending on the relative orientation between scratching and grinding directions. The cracking and delamination of TiN-coated hardmetals when subjected to Brale indentation was studied while varying the microstructure and surface finish of the substrate. In this case, another fine-grained WC-Co cemented carbide with lower binder content (6 wt.%Co) was included in the investigation. It was found that polished and coated hardmetals exhibit more brittleness (radial cracking) and lower adhesion strength (coating delamination) with decreasing binder content. Such a response is postulated on the basis of the influence of intrinsic hardness/brittleness of the hardmetal substrate on both cracking at the subsurface level and effective stress state, particularly regarding changes in shear stress component. On the other hand, grinding was discerned to promote delamination, compared to the polished condition, but strongly inhibits radial cracking. This was the result of the interaction between elastic-plastic deformation imposed during indentation and several grinding-induced effects: remnant compressive stress field, pronounced surface texture, and microcracking within a thin microcracked subsurface layer. It is then concluded that coating spallation prevails over radial cracking as the main mechanism for energy dissipation in ground and coated hardmetals. Contact damage resistance of coated hardmetals with different substrate surface finish conditions was investigated by means of spherical indentation under increasing monotonic loads. It was found that grinding enhanced resistance against both crack nucleation at the coating surface and subsequent propagation into the hardmetal substrate. Hence, crack emergence and damage evolution was effectively delayed for the coated G condition, as compared to the reference P one. The observed system response was discussed on the basis of the beneficial effects associated with compressive residual stresses remnant at the subsurface level after grinding, ion-etching and coating. The influence of the stress state was further corroborated by the lower contact damage resistance exhibited by the coated GTT specimens. Finally, differences observed on the interaction between indentation-induced damage and failure mode under flexural testing pointed in the direction that substrate grinding also enhances damage tolerance of the coated system when exposed to contact loads.
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Liang, Te-Hui. "A numerical study of the contact behaviors in resistance spot welding steel-based sheets /". The Ohio State University, 2000. http://rave.ohiolink.edu/etdc/view?acc_num=osu1488195633520408.
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Beyer, Robert [Verfasser]. "A constitutive contact model for homogenized tread-road interaction in rolling resistance computations / Robert Beyer". Hannover : Technische Informationsbibliothek (TIB), 2017. http://d-nb.info/1128663767/34.
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Jedrzejczyk, Pawel. "Analyse et quantification de l'endurance de contact électrique sous sollicitations de fretting". Thesis, Ecully, Ecole centrale de Lyon, 2010. http://www.theses.fr/2010ECDL0016/document.
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La sollicitation de fretting apparait comme un processus de dégradation très pénalisant dans les multiples systèmes industriels (aéronautique, industrie automobile, industriels du nucléaire, transports ferroviaires etc. …). Ce processus d’usure engendre dans la plupart des cas soit une réparation (rechargement) des surfaces soit le remplacement des composants (situation la plus souvent observée). La sollicitation de fretting est associée à des micro-déplacements alternés entre deux surfaces en contact. On observe généralement ce type de sollicitation dans tous les contacts soumis à des vibrations ou à des cycles thermiques. La sollicitation de fretting usure dans les contacts électriques est particulièrement pénalisante. Outre l’endommagement des surfaces, ce processus induit une augmentation significative de la résistance électrique des contacts et une perte de fonctionnalité du connecteur en particulier dans les connecteurs basses tensions très sensibles aux fluctuations de la résistance électrique. Pour palier ce problème les industriels de la connectique et leurs clients (industriels de l’automobile) cherchent à mettre en place de nouveaux dépôts palliatifs pour résoudre ces problèmes tout en limitant les surcouts liés à l’utilisation de dépôts nobles tels que l’or.Le sujet de cette thèse porte sur cette problématique avec pour objectif de mettre en place une méthodologie de choix des dépôts pour optimiser la durée de vie des connecteurs. L’étude aborde essentiellement l’influence des conditions de chargements mécaniques et plus particulièrement l’amplitude de débattementThe degradation by fretting appears as a very troublesome process in many industrial systems (spatial, automotive, nuclear industry, railway systems etc. …). This wear process makes it necessary to repair or to replace the destroyed component. The process of degradation by fretting is associated with the micro-displacement between two surfaces in contact. This type of degradation is observed in all types of contacts subjected to the vibrations or thermal variations. The degradation by fretting in electrical contact is particularly dangerous. The wear of the contacting surfaces causes a significant increase of the electrical resistance of the contact and the decay of the functional properties of the connector. This situation concerns especially the low tension connectors very sensible to the fluctuations of the electrical resistance. In order to avoid this situation the automotive industry and its suppliers, the manufacturers of the electrical connectors, are looking for new materials and coatings.The objective of this thesis consists to develop the methodology of choice of the coating materials in order to optimise the lifetime of the electrical contact. The study focuses mainly on the influence of the mechanical conditions, the displacement amplitude in particular, on the performance of the electrical connector
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Narayanaswamy, Anand Subramanian. "A Non-Contact Sensor Interface for High-Temperature, MEMS Capacitive Sensors". Case Western Reserve University School of Graduate Studies / OhioLINK, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=case1275675071.
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Barreto, Eduardo Xavier. "Design construtal de caminhos condutivos com geometrias em forma de "i" e "t" para resfriamento de corpos geradores de calor considerando a resistência térmica de contato". reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2015. http://hdl.handle.net/10183/133124.
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Este trabalho trata da aplicação do método Design Construtal para investigar a transferência de calor através de caminhos de alta condutividade térmica com geometrias definidas. O objetivo é obter a configuração que reduz a temperatura máxima em excesso do sistema considerando que as áreas ocupadas pelos materiais de alta e baixa condutividade são tratadas como constantes. Assim, o objeto de estudo é um volume de área finita onde ocorre a geração de calor. O escoamento da energia térmica para fora do volume é feito através de um caminho condutor de alta condutividade térmica. O trabalho considerou a resistência térmica de contato entre o elemento condutivo e o corpo gerador de calor, onde um terceiro material com resistência térmica equivalente à resistência de contato é interposto entre os dois primeiros. Na solução da equação da difusão do calor, foi realizado um tratamento numérico através de um código baseado em elementos finitos e utilizando o toolbox PDETool, Partial Differential Equations Tool, que pertence ao aplicativo comercial MatLab®. O tratamento numérico foi realizado considerando-se caminhos condutivos com geometrias em forma de "I" e em forma de "T", mantendo-se as frações de área constantes e variando-se os comprimentos dos materiais de alta condutividade e os da resistência térmica de contato. A otimização geométrica foi feita considerando-se os graus de liberdade existentes para cada geometria, onde os valores otimizados para a situação ideal, ou de acoplamento térmico perfeito, foram comparados para os resultados envolvendo a resistência térmica de contato (RTC). Os resultados indicam que a RTC pode aumentar a temperatura máxima em excesso, assim como tem efeito significativo sobre as ótimas configurações calculadas quando a resistência de contato é levada em consideração para ambas as configurações "I" e "T" estudadas.This work applies Constructal Design to investigate the heat transfer through high conductive pathways with defined geometries. The objective is to find the configuration which reduces the maximal excess of temperature considering the areas with high and low thermal conductivity are constants. Thus, the object studied here is a volume with a finite area and heat generation. The outside heat flux is conducted through a high thermal conductive pathway. Here, special attention is given to the thermal contact resistance between the high conductive pathway and the solid body, where a third material with a thermal resistance equivalent to the thermal contact resistance is inserted between them. A numerical treatment was given in order to solve the heat diffusive equation. It was used a numerical code based on finite elements and the toolbox – PDETool, Partial Differential Equations Tool, which is part of the MatLab® applicative. The numerical treatment was achieved considering "I" and "T" geometries for the high conductive pathways keeping the areas fraction constants and varying the lengths of both high conductive and the equivalent thermal contact layer materials. The optimization was performed considering the degrees of freedom of each geometry, where the optimized values for the ideal situation, i.e., perfect thermal contact were compared with the results considering the thermal contact resistance. The results indicate that the thermal contact resistance can increase the excess of temperature, as well as it has a significant effect on the optimal configurations when using perfect thermal contact or taking into account the thermal contact resistance for "I" and "T" shaped geometries.
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Luo, Xinhang. "Few-Layer MoS2 Thin Films Grown by Chemical Vapor Deposition". The Ohio State University, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=osu1417656899.
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Bourouga, Brahim. "Etude d'une methode de mesure instationnaire de resistance thermique de contact entre parois cylindriques concentriques minces". Nantes, 1986. http://www.theses.fr/1986NANT2063.
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Developpement d'dune methode de mesure de resistance thermique de contact dans des doubles tubes metalliques minces destines a la fabrication de condenseurs pour des installations nucleaire. La methode, qui fonctionne en regime instationnaire, est basee sur l'analyse de la reponse de l'echantillon a une sollicitation thermique du type echelon temperature
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Wang, Feng. "Controlling the Hydrophilicity and Contact Resistance of Fuel Cell Bipolar Plate Surfaces Using Layered Nanoparticle Assembly". University of Cincinnati / OhioLINK, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1268081049.
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Misra, Prashant. "Simultaneous Studies Of Electrical Contact Resistance And Thermal Contact Conductance Across Metallic Contacts". Thesis, 2009. http://hdl.handle.net/2005/953.
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Contact resistance is the most important and universal characteristic of all types of electrical and thermal contacts. Accurate measurement of contact resistance is important, because it serves as a measure for judging the performance and operational life span of contacts. Rise in contact temperature is one of the major factors that pose a big threat to the stability of electrical contacts. Dissipation of heat by solid conduction through a contact interface is governed by its thermal contact conductance (TCC). This emphasizes the need to study the TCC of an electrical contact along with its electrical contact resistance (ECR). Simultaneous measurement of ECR and TCC is important for understanding the interconnection between these two quantities and the possible influence of one over another. Real time experimental data and analytical correlations can be extremely helpful in developing electrical contacts with improved thermal management capabilities.
As a part of the experimental investigation, a test facility has been developed for making simultaneous measurement of ECR and TCC across flat contacts. The facility has the capability of measuring ECR and TCC over a wide range of operating parameters, such as contact pressure, contact temperature, interstitial gaseous media, ambient pressure, etc. It is also capable of determining the electrical resistivity and thermal conductivity of materials as a function of temperature, which is very helpful in analyzing the generated contact resistance data. Using this facility, simultaneous ECR and TCC measurements are made across bare and gold plated contacts of OFHC Cu (oxygen free high conductivity copper) and brass.
Simultaneous ECR and TCC measurements are made on nominally flat contacts in the contact pressure range of 0 – 1 MPa and the interface temperature range of 20 – 120 °C. Effect of contact pressure and interface temperature on ECR and TCC is studied on bare and gold coated contacts in vacuum, N2, Ar, and SF6 environments. TCC strongly depends on the thermophysical properties of the interstitial media and shows a significant enhancement in gaseous media, because of the increased interfacial gap conductance compared to vacuum. The gas pressure is varied in the range of 1 – 2.6 bar to study its effect on the gap conductance at different contact pressures and interface temperatures. Minor increase in the ECR observed in gaseous media is found to be independent of the properties of the media. Experimental results indicated that ECR depends on the gas pressure as well as on the applied contact load. Effect of gold coating and its thickness on the ECR and TCC across OFHC Cu and brass contacts is studied. Measurements on electroplated gold specimens having different gold layer thicknesses (0.1, 0.3, and 0.5 µm) indicated that ECR decreases and TCC increases with increasing gold coating thickness. Effect of gold coating on the substrate properties, contact surface tomography, and microhardness is analyzed and correlated to the observed behavior of ECR and thermal gap conductance. An attempt is made to understand and quantify the changes in the contact surface characteristics due to contact loading and heating, by measuring various surface topography parameters before and after the experimentation. Effect of thermal stresses (generated due to temperature variations) on ECR and TCC is studied and inclusion of an experimentally measured temperature dependent load correction factor is suggested in the theoretical models to take into account the effect of thermal stresses in contact assemblies.
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Gonzalez, Castro Gabriela, Maksims Babenko, S. Bigot, John Sweeney, Hassan Ugail i Benjamin R. Whiteside. "Thermal contact resistance in micromoulding". 2011. http://hdl.handle.net/10454/5425.
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yesThis work outlines a novel approach for determining thermal contact resistance (TCR) in micromoulding. The proposed technique aims to produce TCR predictions with known confidence values and combines experimental evidence (temperature fields and contact angle measurements) with various mathematical modelling procedures (parametric representation of surfaces, finite element analysis and stochastic processes). Here, emphasis is made on the mathematical aspects of the project. In particular, we focus on the description of the parametric surface representation technique based on the use of partial differential equations, known as the PDE method, which will be responsible for characterizing and compressing micro features in either moulds or surface tools.
EPSRC
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Oloumi, Arusha. "Cell-cell contact induced resistance to etoposide". Thesis, 2002. http://hdl.handle.net/2429/13531.
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Many tumour cell lines grown in close three dimensional cell-cell contact either as
multicell spheroids or tumours in mice exhibit a form of multicellular drug and radiation
resistance that has been called the "contact effect". This resistance is often associated
with agents that produce DNA double-strand breaks such as ionizing radiation and the
anticancer drug and topoisomerase II inhibitor, etoposide. The hypothesis was that
growth in three dimensional contact results in changes in gene expression that act,
directly or indirectly, to increase resistance to etoposide. The objectives were to 1)
determine the mechanism for etoposide resistance of spheroids, 2) identify genes that are
differentially expressed in monolayers and spheroids, and 3) based on these results,
examine the importance of intracellular free calcium levels as mediators of contact
resistance.
Cycling cells from Chinese hamster V79 spheroids are about 10 times more resistant
than monolayers to cell killing by etoposide. Previous results indicated that the outer
cells of spheroids and monolayers contained the same total amount and activity of the
target enzyme, topo lice, and grew at the same rate. Using immunoblotting and
immunohistochemistry, topo Hoc was found to be localized primarily in the cytoplasm of
the proliferating outer cells of V79, SiHa and C6 spheroids, while nuclear localization
was observed in their corresponding monolayers. Conversely, only WiDr cells, which
did not show an increase in resistance to etoposide when grown as spheroids,
demonstrated a predominantly nuclear localization of topo Ila. This difference in
localization pattern was subsequently explained by the 10-fold decrease in
phosphorylation of topo Ila in spheroids relative to monolayers, since phosphorylation is
apparently required for nuclear translocation of this enzyme. Cells sorted from xenograft
tumours grown in immunodeficient mice resembled the spheroid pattern both in terms of
sensitivity to etoposide and location of topo Hoc. When the outer cells of V79 spheroids
were returned to monolayer growth, the rate of redistribution of topo Hot to the nucleus
occurred with the same kinetics as the increase in sensitivity to the cytotoxic effects of
etoposide. Thus, close 3-dimensional cell-cell contact can lead to a change in posttranslational
modification of topo Hoc that results in resistance to etoposide.
A more direct approach was taken to identify changes in gene expression that occur
when cells are grown as spheroids. Using the technique of differential display, 8
reproducible genes were found to be differentially expressed in the outer layer of V79
spheroids compared to monolayers. Up-regulation of 3 genes (cytochrome oxidase c,
mtsl and calretinin) was associated with an increase in calcium binding capacity in outer
cycling cell of spheroids, suggesting a possible role for calcium for the development of a
contact effect. Consistent with this hypothesis, a 2-fold lower concentration of
intracellular calcium was found in spheroids compared to monolayers using fluo-3 as a
calcium indicator dye. Exposure of monolayers and outer spheroid cells to non-cytotoxic
concentrations of BAPTA-AM, a calcium chelating agent, eliminated the difference in
etoposide sensitivity between V79 monolayers and spheroids. Calcium depletion has
been previously shown to protect against etoposide-induced damage by affecting both the
phosphoryaltion of topo Ila and by stablizing the cleavable complex. To determine
whether over-expression of a calcium binding protein would increase resistance to
etoposide, V79, SiHa and C6 monolayers were transduced with metastasin (mtsl).
Expression of this transgene did not reduce killing by etoposide, however because the
ultimate goal of reduction in intracellular free Ca²⁺ was also not achieved with this
method, the importance of calcium regulation in etoposide resistance cannot be ruled out.
In conclusion, growth of cells in 3-dimensional contact as spheroids or as solid
tumours induces resistance to etoposide. The basis for this resistance could lie in a
change in intracellular Ca²⁺ that alters cleavable complex formation and affects
phosphorylation of topo Ila, both of which can cause resistance to the anti-cancer drug
etoposide.
33
Lin, Ching-Ting, i 林敬庭. "Improving Contact Resistance of Molybdenum Disulfide Transistor". Thesis, 2016. http://ndltd.ncl.edu.tw/handle/58554630904620697412.
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碩士國立交通大學
電子研究所
105
The atomic thickness of 2D materials effectively mitigates the short channel effect, and opens up new possibilities to scale device and extend the Moore’s law. Among 2D materials, transition metal dichalcogenides-MoS2 has attracted many attentions as the channel material of the transistor and prompted new developments of numerous electric and optical devices. However, large contact resistance limited the MoS2 transistor performance. We synthesize monolayer MoS2 on sapphire substrate by chemical vapor deposition method, and then transfer MoS2 film to HfO2 dielectric substrate. We carefully engineer the interface between source/drain (S/D) metal and MoS2 to find stable methods for reducing contact resistance. In this thesis, sulfur vacancies generated by H2 plasma treatment was found to result in band gap narrowing from optical analysis and VASP simulation. If only S/D region received the H2 plasma treatment, the band gap narrowing reduced the Schottky barrier between S/D metal and MoS2 and therefore reduced contact resistance. F- and Cl-based plasma treatment induced p-type doping in MoS2 transistors, and improved the p-type conduction of WSe2 transistors after the Cl2 plasma treatment. A SiO2 capping layer was utilized to suppress the potential damage of the device fabrication process on monolayer MoS2. Furthermore, the SiO2 capping layer influences the contact between S/D metal and MoS2 due to charge transfer. Replacing S/D metal from Mo to Pd, which has a higher work function and less interaction with MoS2, shows reduced contact resistance. Although the Schottky barrier is higher, a large band bending can be achieved by applying gate voltage. We attributed this to the less interaction between Pd and MoS2.
34
Chen, Ming-Lei, i 陳明磊. "The research of ohmic contact and specific contact resistance on p-GaN". Thesis, 2005. http://ndltd.ncl.edu.tw/handle/05653274888356430456.
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Chia-Chin, Chuang, i 莊家慶. "Contact Temperature and Thermal Contact Resistance Based on a Fractal Surface Model". Thesis, 2001. http://ndltd.ncl.edu.tw/handle/76841294677409212277.
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碩士國立臺灣大學
機械工程學研究所
89
On the interface between two apparently conforming solids, only some asperities are really in contact. The real contact area is much less than the apparent contact area. Most of the heat or energy can only pass through these small contact areas. This distortion of the heat flow causes an increase in thermal resistance that is known as the thermal contact resistance. To date, the influence of surface roughness on the contact resistance and temperature has not been clearly identified. Existing theories on contact temperature and resistance have two major shortcomings: the first one is that they employed non-fractal surface models; the other one is that they neglected the effects of thermal deformation. Use of non-fractal models makes it difficult to unambiguously identify the parameters of surface models. Because of the neglect of thermal deformation, existing models can not simulate the directional effect of contact resistance. In this thesis, we study the thermal contact resistance by employing a fractal surface model and considering the effects of thermal deformation. First, we determine the relationship between the contact temperature, deformation and contact pressure of a single asperity. Then the force equilibrium and compatibility conditions are employed to find the contact force, the total heat passing through the interface, and the associated contact resistance. At last, we study quantitatively the effects of material properties, fractal dimensions, contact pressure, temperature and the direction of heat flow on the contact temperature and resistance.
36
Prasad, V. Siddeswara. "Studies On Electrical Contact Resistance And Coefficient Of Friction Across Sliding Electrical Contacts". Thesis, 2010. http://etd.iisc.ernet.in/handle/2005/1534.
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Simultaneous measurement of electrical contact resistance (ECR) and coefficient of friction (COF) at the sliding interface is essential to assess the performance of selected material contact pairs for the transfer of current from stationary member to moving member (or vice-versa). Low and stable values of ECR and COF are desirable during the intended operating life of the contact members. These parameters may change with respect to time as a consequence of change in the surface properties of contact members due to their relative movement. Hence experimental investigations have been conducted to study the variation of ECR and COF while different riders sliding on copper and brass flat samples in different environments. As a part of the experimental investigation, a reciprocating sliding setup is designed and developed to study the variation of ECR and COF in terms of normal force, sliding speed, current and environment. The details of the experimental setup are described along with its construction and operation. The sample preparation, instrumentation, data acquisition and presentation are explained in detail. The variations of ECR and COF at different normal forces, currents and sliding speeds by moving OFHC copper, brass, silver, Ag10Cu and Ag20Cu riders on OFHC copper and brass flat samples in vacuum, argon, nitrogen and air are studied in detail. Studies are also conducted to evaluate the performance of metallic contacts under lubricated condition using general purpose lubricating oils of different viscosity.
Metallic contacts show a decrease in ECR with increase in normal force at all sliding speeds in all media. Sliding metallic contacts show a significant decrease in both ECR and COF during the initial sliding cycles at constant normal force in all media. Surface roughness of flat sample is found to have a significant effect on both ECR and COF in all media. Wear of rider is found to be significant as compared to wear of flat samples. Metallic contacts show an inverse relationship between ECR and COF in all media under mild wear regime (0.2< COF≤ 0.4). ECR and COF of sliding metallic contacts are independent of current (≤ 4A) in mild wear regime in all media. Reasonably low values of ECR and COF are observed for prolonged duration with lubricants having low viscosity. The presence of wear fragments at the sliding zone is found to have significant effect on both ECR and COF in all media. Low values of ECR are observed while copper rider sliding on brass sample as compared to silver rider under same operating conditions. Significant amount of metal transfer is observed with silver based riders sliding on copper and brass flat samples in different media. The present investigations are useful in understanding the contact behaviour of copper and brass flat samples for similar and dissimilar riders sliding on them in various environments.
37
Kao, Ming-Hong, i 高銘鴻. "A Study on the Contact Resistance Reduction in Metal/n-type Germanium Contacts". Thesis, 2012. http://ndltd.ncl.edu.tw/handle/58001522062615986997.
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碩士國立交通大學
電子研究所
101
With the rapid progress of nano-fabrication technology, Si based MOSFETs have been successfully scaled down to 20 nm regime. However, the continued scaling will be a problem due to several physical and technical limitations, and the device performance may not be improved by further scaling down. Many methods have been purposed to solve this problem, because of the higher carrier mobilities and better process compatibility, Ge is considered a potential candidate to replace silicon as the next generation channel material. However, the contact resistance between metal and n-type Ge is very high due to the high Schottky barrier height. To implement high performance Ge NMOSFETs, reducing the contact resistance of metal/n-type Ge is critical. In this thesis, two different methods to reduce the contact resistance of metal/n-type Ge are investigated. One is inserted dielectric-inserted junction and the other is modified Schottky barrier junction. The former is to modulate the Schottky barrier height and the latter is to enhance the doping concentration at the metal/Ge interface. The dielectric insertion method has been reported in literature. Both Al2O3 and TiO2 have been used as the inserted dielectric layer. Because of the lower conduction band offset of TiO2 to Ge, it can not only reduce the Schottky barrier height but also achieve low tunneling resistance and high conduction current. However, the mechanism has not been well understood. In this thesis, we first observed that the Fermi level pinning effect is a very weak function of the TiO2 thickness so we infer that the Schottky barrier height reduction by the dielectric insertion is due to the change of the pinning position. The amount of fixed charges in the thin dielectric layer is extracted from a MIS structure and it is found that the small amount of fixed charges is not sufficient to produce such a pronounced voltage drop to modulate the Schottky barrier height. It is thus recommended that the mechanism of the dielectric insertion method mainly comes from interface dipoles. Besides, it is observed that after annealing at 300 °C for 30 minutes, the Schottky barrier height will increase. The increase of the Schottky barrier height increase with the increasing of the annealing temperature. According to the microstructural analysis, it is postulated that the crystallization of the dielectric layer after annealing is the main reason for the increase of Schottky barrier height. Due to the dielectric constant increase after crystallization, the capacitance of the dielectric capacitor increases and causes smaller voltage drop so that the Schottky barrier height increases. The thicker TiO2 dielectric layer has smaller capacitance, which might be the reason for the lower Schottky barrier height. In the modified Schottky barrier method, dopants are implanted into metal-germanide instead of Ge so that the number of defects formed in substrate could be negligible, which would mitigate the dopants diffusion caused by the interaction between defects and dopants. A thin and high doping concentration layer can be formed at the metal/semiconductor interface. Increasing the activation temperature will achieve higher doping concentration. But the allowed annealing temperature is limited by the poor thermal stability of NiGe films. To improve the thermal stability of NiGe films, a Si layer is inserted between Ni and Ge before annealing. The result shows that the thermal stability of NiGe film is improved by this Si-insertion layer from 500 °C to 550 °C. Using the Si-insertion technique, the activation temperature of MSB junctions can be raised to 550 °C so that the doping concentration is enhanced. Compared to the conventional junction with direct implantation into Ge, the junction depth is much shallower and the carrier concentration is much higher for the MSB junction which suggests that the MSB process is attractive for the short channel Ge MOSFETs. In summary, this thesis proposed the mechanism of the Schottky barrier height modulation by dielectric insertion. The thickness effect and annealing effect are also explained. A new method, modified Schottky barrier method, is propsed to reduce the contact resistance between metal and n-type Ge by forming a thin and high concentration layer at the metal/Ge interface. This method is very promising for short channel Ge NMOSFET.
38
Jain, Rajiv. "ECR Studies Across Bare And Gold Coated Metal Contacts At Low Temperatures". Thesis, 2009. http://hdl.handle.net/2005/1036.
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Electrical contact resistance (ECR) measurements are needed for judging the performance of electrical appliances. Understanding the behaviour of ECR at low temperature gives a unique opportunity for understanding the contact mechanism itself and controlling the contact resistance for its applications in various areas at these temperatures. In many high-end applications, sophisticated electronic devices are being operated below ambient temperature to improve their performance. The availability of cryogens, improvement in Thermo-Electrical (TE) based Peltier coolers, accelerated the development of these devices. In designing such systems, an accurate measurement of electrical contact resistance below room temperature is important.
A detailed experimental investigation has been conducted on electrical contact resistance across bare and coated metal contacts at low temperatures. As a part of the experimental investigation, a test facility capable of varying the contact force, surrounding pressure and temperature, is developed. The design, construction, testing and use of this facility are described. Electrical contact resistance at different contact pressures across copper, OFHC copper and brass with and without gold coatings is measured using 4-wire technique with high accuracy. The test specimen preparation, instrumentation and data acquisition are explained in detail. The setup is standardized by comparing the experimental results obtained across copper-copper contacts in vacuum with the theoretical model. The electrical contact resistance is measured as a function of contact force at different temperatures. The effect of loading and unloading, and the existence of hysteresis are experimentally studied. The electrical properties of conductors improve at low temperature but this is not true for contact resistance. At low temperature the contact resistance increases and it depends on applied contact force, hardness and roughness of the contacting surfaces. Gold-coated contacts exhibited an increase in contact resistance at low temperatures.
39
Lin, Chung-pao, i 林忠寶. "Low specific contact resistance and high reflectivity of Pt/Ag contacts on p-GaN". Thesis, 2008. http://ndltd.ncl.edu.tw/handle/73365001469281437989.
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碩士國立中央大學
化學工程與材料工程研究所
96
The electrical and optical properties of metal scheme contacts on p-GaN were investigated widely. In this paper, firstly, we studied the transmittance of Pt ohmic layer on p-GaN. Then, the contact resistance and reflectivity of Pt / Ag was evaluated. Pt p-contact with two different thickness 5 and 10 nm were studied on p-GaN. Pt / p-GaN samples were annealed at N2 ambient for 5 minutes and annealing temperatures were 500℃~800℃. We find the specific contact resistance and transmittance of Pt raise with increasing annealing temperatures. After specific contact resistance and transmittance measurement, 150 nm Ag layer was deposited on the annealed Pt contact pads. Finally, the metal scheme of Pt/Ag/p-GaN was investigated by annealing together at at N2 ambient for 5 minutes and annealing temperature was 500℃. The lowest specific contact resistance of Pt / Ag we can get is about 4.5x10-3 Ω-cm2。 At 470 nm, the highest reflectivity of Pt / Ag is about 83%.
40
Jia-BinChen i 陳加彬. "A study of graphene to graphene contact resistance". Thesis, 2016. http://ndltd.ncl.edu.tw/handle/n8kgrk.
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41
Ya-PeiTseng i 曾雅珮. "Analysis of IC Socket Spring Pin Contact Resistance". Thesis, 2010. http://ndltd.ncl.edu.tw/handle/96341549913303846524.
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碩士國立成功大學
工程科學系專班
98
The manufacturing of an IC electronic device goes through various processes from wafer fabrication to assembly, experiencing different levels of tresses and risks. The final test validates the functionality of each DUT (Device Under Test) in the package form before its shipment. BGA sockets with spring pins acting as an interface between the load board and the DUT during testing are high-price consumables. The quality of sockets determines the yield of the IC testing. However, the performance of a socket decreases with the increasing number of touches and can cost a lot if it is replaced wrongly. Therefore, to get the balance between quality and cost of sockets, a counter embedded in the BGA socket is used to record the number of touches between the pins and solder balls in this study. Thus, wear of the four contact points of the spring pin to the solder ball can be monitored to see its effect on the contact resistance real time. The results show that there is variation in contact resistance even in new pins. Thus, the time of replacing individual pins due to wear varies. The increase in contact resistance is mainly caused by wear and arcing as the number of touches increase. On the other hand, the spring force of individual pins is not significantly affected by the number of touches; namely, the spring force is not a good indicator of pin wearing. A meter system is designed and deployed in this study to monitor the increase in contact resistance so that the socket quality can be assured. Keywords: Device testing, IC socket, Spring pin, Contact resistance
42
Zhan, Tian-Hao, i 詹天皓. "Study on contact resistance of PtSi/poly-Si". Thesis, 1993. http://ndltd.ncl.edu.tw/handle/76918280060200274511.
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43
Yang, Wen-Lu, i 楊文祿. "A study of contact resistance for VLSI metallization". Thesis, 1992. http://ndltd.ncl.edu.tw/handle/42104773117133745180.
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44
Lin, Tsung-Hsin, i 林宗信. "Contact Temperature and Thermal Contact Resistance Based on a Random Cantor Set Surface Model". Thesis, 2008. http://ndltd.ncl.edu.tw/handle/10661054557548262413.
Pełny tekst źródłaStreszczenie:
碩士國立臺灣大學
機械工程學研究所
96
This paper studies the contact temperature and thermal resistance at the interface of two solids. Two different cases are considered: (1) sliding contact with Coulomb friction and (2) static contact while the two surfaces have different temperatures. When two surfaces are in contact, the load-displacement relationship and the interfacial heat conduction depend on the surface topography as well as the material properties of the contact solids. Most surface models treat the rough surface as a collection of asperities with a fixed shape. The heights of the asperities are distributed stochastically. However, recent studies showed that conventional geometrical parameters used to characterize the shape of the asperities depend on the resolution of the roughness-measuring instrument. This result suggests the use of fractal geometry for the characterization of surface roughness. In this thesis, we construct a random fractal surface model based on the Cantor set. We study the situation where a random Cantor surface is in contact with a rigid insulated smooth surface. Given the probability density functions of the random fractal parameters, we derive the expectations and standard deviations of the applied load, contact temperature, and thermal resistance. Finally, the Monte-Carlo simulation is employed to verify the analytical results.
45
Hou, Kai-hsiang, i 侯凱翔. "Low contact resistance current collectors for lithium ion batteries". Thesis, 2012. http://ndltd.ncl.edu.tw/handle/29zd9t.
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碩士逢甲大學
材料科學所
100
Current collectors with low contact resistance for lithium ion batteries have been investigated in this thesis. Four types of current collectors, including AISI 304 stainless steel and three types of carbon coated stainless steels, were used for LiMn2O4/LiFePO4 electrodes to perform the capacity under C-rate charge-discharge. The carbon films were deposited on AISI 304 stainless steel by chemical vapor deposition (CVD). The types of carbon films were controlled by concentration of carbon source with C2H2/H2 ratio of 0.15, 0.45 and 1.4, respectively, and CVD reaction temperature of 810 oC. The three types of carbon coating are carbon filament (CF), carbon sphere (CS), and carbon transition (CT, a transition type in-between carbon filament and sphere), respectively, based on those surface morphologies. CT-typed current collector unequivocally demonstrate a remarkable improvement on capacity under all current rates particularly at high C-rate(10C). The CS and CT composed of continuous carbon layers are found to greatly reduce the contact resistance between the electrode layer and the current collector. We also found that the ohmic drop decreases at high rate resulting from carbon layer coating. The overall charge-transfer resistance can be reduced by carbon-coated current collector according the results of Nyquist plots. Therefore, the power performance of Li-ion batteries is enhanced by ~55%.
46
Khatiwada, Mahesh, i 馬哈仕. "Investigation of Thermal Interface Materials to reduce contact resistance". Thesis, 2019. http://ndltd.ncl.edu.tw/handle/esexh4.
Pełny tekst źródłaStreszczenie:
碩士國立交通大學
機械工程系所
107
Advancement of the modern generation for fast, reliable and small computing devices has led to development of high power density per unit area. Most of this heat is to be dissipated using the various heat sinks. The unevenness or roughness of these surfaces offer the resistance to the flow of heat from the heat source to heat sink. This resistance on the contact due the roughness of the surface known as Thermal Contact Resistance (TCR) has to be minimized for effective heat transfer from heat source to heat sink. Using Thermal Interface Material (TIM) between the contact surfaces has been the effective way to reduce the thermal contact resistance. Decrease of surface roughness significantly reduces the contact resistance. Moreover, study on effect of pressure and surface temperature on TCR was performed. It clearly indicates increase of pressure and temperature decreases TCR. The decrement depends on the TIM used. TCR variation on Thermal cycling loading also depends on the Tim used. Similarly study of variation of power supply has effect on the TCR if the TIM melts on the maximum power. An attempt has been made to address the problem of oozing out when TIM that melts is used.
47
TUNG, LIN CHIEN, i 林建通. "Experimental Study on Thermal Contact Resistance and Contact Pressure of Aluminum Blocks and Aluminum Honeycombs". Thesis, 2003. http://ndltd.ncl.edu.tw/handle/75726918967179720914.
Pełny tekst źródłaStreszczenie:
碩士大葉大學
機械工程學系碩士班
91
This thesis is divided into two parts: the first part is “Research on Thermal Contact Resistance and Interfacial Pressure of Aluminum Blocks”, and the second part is “Research on Thermal Contact Resistance and Interfacial Pressure of Aluminum Honeycombs”. The first part of this thesis was an experimental study of thermal contact resistance conducted with metallic contacts across bolted joints. Three types of interfaces were considered, including Al/Al, Cu/Al, and SS/Al contacts. The aluminum sample has a square cross section (63.5 mm × 63.5 mm) and a height of 50 mm. The bolt patterns included 4 and 8 bolt configurations. The bolt shaft diameter was 8 mm. The contact pressure of bolted interfaces was measured by the pressure-measuring film through an image processing technique. Results indicate that the contact pressure increases with the torque applied on bolts. The contact pressure also increases with either an increase in the number of bolts, or a decrease in the surface roughness of contacting surfaces. The thermal contact resistance of bolted junctions depends strongly on the interfacial contact pressure. Correlation of interfacial pressure was developed in terms of the torque and bolt-joined parameters. Contact resistance correlation was expressed as a function of the contact pressure, surface roughness, and material properties. Both correlations were in reasonable agreement with the experimental data obtained in this study. The second part of this thesis was to study experimentally the thermal contact resistance and interfacial pressure of aluminum honeycombs. The honeycomb used in this study was made of Al3104-H19. The cell diameters of honeycombs were 6.3 and 12.7 mm. Temperature measurement shows that the temperature drop across the honeycomb sample is lower for the honeycomb with a smaller cell diameter. In order to further investigate the influence of sample heights on contact resistance, the honeycomb samples with two different heights were adopted. Results indicate that the total thermal conductance is higher for samples with a smaller cell diameter. The increase of the number of bolts leads to an increase of the total conductance. The contact resistance between aluminum honeycomb and aluminum alloy sample is about 7% of the total resistance. In addition, the contact resistance of honeycombs with a cell diameter of 6.3 mm decreased with the increasing torque. However, for the honeycombs with a cell diameter of 12.7 mm, the torque and the bolt pattern produce nearly no influence on the thermal contact resistance. The contact resistance is almost independent of the honeycomb height, but the total resistance decreases with increasing the height of samples.
48
Lin, Tai-Ming, i 林泰名. "Development of Ohmic Contacts with Low Surface Roughness and Low Contact Resistance on AlGaN/GaN HEMTs". Thesis, 2012. http://ndltd.ncl.edu.tw/handle/08365759460063234980.
Pełny tekst źródłaStreszczenie:
碩士國立交通大學
材料科學與工程學系
101
The characteristics of Ohmic contacts on GaN high electron mobility transistors (HEMTs) have profound influence to the DC and RF performance. The most critical issue for Ohmic contacts on GaN HEMTs is the roughness of the surface morphology caused by interdiffusion of metals under high temperature annealing. The rough surface morphology will cause difficulty in E-beam lithography aligner and potential degradation in device performance and reliability. In this study, I optimized the surface morphology of the Ohmic contact on GaN HEMTs with improved barrier layer thickness. The Ti/Al/Ti/Ni/Au (20/120/40/60/50 nm) metal scheme shows a low specific contact resistivity (ρc) of 3.9x10-6Ωcm2 and a smooth surface morphology of 27.6nm root mean square roughness (Rrms) after annealed at 870℃for 35 seconds. This metal scheme is then analyzed by transmission electron microscope (TEM) and X-ray diffractormeter (XRD) to figure out the formation mechanism of it. According to the analytic results, formation of large flat AlNi grains that lay on the TiN stripe rather than surrounded by Al-Au might be the reason for improved surface morphology. With moderate Ti and Ni barrier layer thickness, the formation of Al-based intermetallics could be confined. Moreover, the second Ti layer would form thick TiN above AlGaN that might facilitate the tunneling mechanism of Ohmic contact. Finally, the optimized Ohmic contact was applied to make the HEMT devices, and the DC characteristics are as shown below: VDmax about 490mA/mm at Vg =0V, peak gm about 170mS/mm and VBR larger than 100V.
49
Shih, Che-Ju, i 施哲儒. "A Study on the Nickel Germanide Contacted N+-P Germanium Shallow Junction and Contact Resistance". Thesis, 2013. http://ndltd.ncl.edu.tw/handle/75953686017457551375.
Pełny tekst źródłaStreszczenie:
碩士國立交通大學
電子工程學系 電子研究所
102
In the past several decades, the research on Si-based devices progresses very fast. Furthermore, the Si-based MOSFETs have been successfully scaled down to 20 nm regime. However, scaling down the devices becomes more and more difficult and reaches the physics limits soon. Therefore, developing another ways to promote the device performance is necessary. Using new semiconducting materials is a way to improve performance. Because germanium has higher mobility and process compatibility for MOSFET fabrication process, germanium is considered to replace Si as the channel material in the future. Nevertheless, the n-type dopant diffusion in germanium is fast so that it is not easy to form shallow n+/p junction, and the high Schottky barrier height at the metal/n-Ge interface causes a high contact resistance due to the Fermi level pinning near the Ge valance band at the interface between metal and germanium. Therefore, the thesis would focus on the forming of shallow n+/p-Ge junction and low resistance metal/n-Ge contact. Because NiGe has the lowest resistivity and low temperature formation, NiGe is selected as the contact metal. The implantation before germanide (IBG) process means ion implantation is performed before germanide formation, and the implantation after germanide (IAG) process means ion implantation is performed after germanide formation. For the IBG junctions fabricated on heavily-doped substrate, very poor junction characteristic is observed by high dose phosphorous ion implantation due to the fast diffusion of Ni by virtue of defects which are generated by ion implantation. Fluorine ion implantation before NiGe formation could effectively suppress Ni diffusion and reduce the leakage current. Moreover, better junction characteristic can be obtained by low dose ion implantation due to the less defects resulting in less Ni diffusion. However, fluorine implantation before NiGe formation would enhance the Ni diffusion to degrade junction characteristic because the fluorine ion implantation induces extra defects. Next, on the lightly-doped substrate, good junction characteristic is more easily to be obtained than on heavily-doped substrate because the deeper junction depth on lightly-doped substrate so that the Ni diffusion would not destroy the junctions. In particular, after NiGe formation, the forward current obviously increases owing to the dopant segregation at the NiGe/Ge interface. Furthermore, either phosphorous or arsenic n+/p junction would have the dopant segregation effect. The arsenic n+/p junctions have relatively low activation concentration inferred by the I-V characteristic. Finally, because the IAG junctions have poor junction characteristic due to the segregated n+ layer is too thin to maintain good n-p junction and the Ni fast diffusion induces large leakage current, the IBG+IAG process is proposed. The IBG+IAG junction could achieve shallow junction depth and raise the forward current at the same time. Furthermore, the measured contact resistance of the IBG junction is about 2x10-5 -cm2 and the lowest contact resistance of IBG+IAG junction is 2x10-6 -cm2.Therefore, this thesis has formed a junction with shallower junction depth, lower leakage current, and lower contact resistance in comparison with previous studies. This achievement is expected to improve the performance of Ge nMOSFETs.
50
黃惟孝. "Measurement and failure analysis of wafer probe testing contact resistance". Thesis, 2004. http://ndltd.ncl.edu.tw/handle/09657629533550316724.
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