Dissertations / Theses on the topic 'High dielectric materials'
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Pliakostathis, Konstantinos. "Novel dielectric resonator antennas based on high permettivity dielectric materials." Thesis, University of Essex, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.410507.
Full textYu, Chuying. "Dielectric materials for high power energy storage." Thesis, Queen Mary, University of London, 2017. http://qmro.qmul.ac.uk/xmlui/handle/123456789/24852.
Full textBraganza, Clinton Ignatuis. "High Dielectric Constant Materials Containing Liquid Crystals." Kent State University / OhioLINK, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=kent1248065159.
Full textTanner, Carey Marie. "Engineering high dielectric constant materials on silicon carbide." Diss., Restricted to subscribing institutions, 2007. http://proquest.umi.com/pqdweb?did=1459913391&sid=1&Fmt=2&clientId=1564&RQT=309&VName=PQD.
Full textLu, Jiongxin. "High dielectric constant polymer nanocomposites for embedded capacitor applications." Diss., Atlanta, Ga. : Georgia Institute of Technology, 2008. http://hdl.handle.net/1853/26666.
Full textCommittee Chair: Wong, C. P.; Committee Member: Jacob, Karl; Committee Member: Liu, M. L.; Committee Member: Tannenbaum, Rina; Committee Member: Wang, Z. L.. Part of the SMARTech Electronic Thesis and Dissertation Collection.
Chen, Minghan. "Optical studies of high temperature superconductors and electronic dielectric materials." [Gainesville, Fla.] : University of Florida, 2005. http://purl.fcla.edu/fcla/etd/UFE0012986.
Full textChristensen, Justin. "Electron Yield Measurements of High-Yield, Low-Conductivity Dielectric Materials." DigitalCommons@USU, 2017. https://digitalcommons.usu.edu/etd/6694.
Full textSun, Xiao. "Characterization and Fabrication of High k dielectric-High Mobility Channel Transistors." Thesis, Yale University, 2014. http://pqdtopen.proquest.com/#viewpdf?dispub=3578458.
Full textAs the conventional scaling of Si-based MOSFETs would bring negligible or even negative merits for IC's beyond the 7-nm CMOS technology node, many perceive the use of high-mobility channels to be one of the most likely principle changes, in order to achieve higher performance and lower power. However, interface and oxide traps have become a major obstacle for high-mobility semiconductors (such as Ge, InGaAs, GaSb, GaN...) to replace Si CMOS technology.
In this thesis, the distinct properties of the traps in the high-k dielectric/high-mobility substrate system is discussed, as well as the challenges to characterize and passivate them. By modifying certain conventional gate admittance methods, both the fast and slow traps in Ge MOS gate stacks is investigated. In addition, a novel ac-transconductance method originated at Yale is introduced and demonstrated with several advanced transistors provided by collaborating groups, such as ultra-thin-body & box SO1 MOSFETs (CEA-LETI), InGaAs MOSFETs (IMEC, UT Austin, Purdue), and GaN MOS-HEMT (MIT).
By use of the aforementioned characterization techniques, several effective passivation techniques on high mobility substrates (Ge, InGaAs, GaSb, GeSn, etc.) are evaluated, including a novel Ba sub-monolayer passivation of Ge surface. The key factors that need to be considered in passivating high mobility substrates are revealed.
The techniques that we have established for characterizing traps in advanced field-effect transistors, as well as the knowledge gained about these traps by the use of these techniques, have been applied to the study of ionizing radiation effects in high-mobility-channel transistors, because it is very important to understand such effects as these devices are likely to be exposed to radiation-harsh environments, such as in outer space, nuclear plants, and during X-ray or UHV lithography. In this thesis, the total ionizing dose (TD) radiation effects of InGaAs-based MOSFETs and GaN-based MOS-HEMT are studied, and the results help to reveal the underlying mechanisms and inspire ideas for minimizing the TID radiation effects.
Xu, Jianwen. "Dielectric Nanocomposites for High Performance Embedded Capacitors in Organic Printed Circuit Boards." Diss., Georgia Institute of Technology, 2006. http://hdl.handle.net/1853/11525.
Full textRao, Yang. "High dielectric constant materials development and electrical simulation of embedded capacitors." Diss., Georgia Institute of Technology, 2001. http://hdl.handle.net/1853/20014.
Full textForesi, James S. (James Serge). "Optical confinement and light guiding in high dielectric contrast materials systems." Thesis, Massachusetts Institute of Technology, 1997. http://hdl.handle.net/1721.1/10381.
Full textMoulart, Alexandre Marc. "High dielectric and conductive composites for electromagnetic crystals." Thesis, Georgia Institute of Technology, 2002. http://hdl.handle.net/1853/17092.
Full textHan, Lei. "Investigation of Gate Dielectric Materials and Dielectric/Silicon Interfaces for Metal Oxide Semiconductor Devices." UKnowledge, 2015. http://uknowledge.uky.edu/ece_etds/69.
Full textMudanai, Sivakumar Panneerselvam. "Gate current modeling through high-k materials and compact modeling of gate capacitance." Access restricted to users with UT Austin EID Full text (PDF) from UMI/Dissertation Abstracts International, 2001. http://wwwlib.umi.com/cr/utexas/fullcit?p3038191.
Full textHinedi, Mohamad Fahd 1964. "HIGH FREQUENCY DIELECTRIC PROPERTIES OF POLYIMIDES FOR MULTILAYER INTERCONNECT STRUCTURES." Thesis, The University of Arizona, 1987. http://hdl.handle.net/10150/276497.
Full textElmezughi, Abdurrezagh, and s3089087@student rmit edu au. "Investigation of Methods for Integrating Broadband Microstrip Patch Antennas." RMIT University. Electrical and Computer Engineering, 2009. http://adt.lib.rmit.edu.au/adt/public/adt-VIT20090305.093332.
Full textWestlinder, Jörgen. "Investigation of Novel Metal Gate and High-κ Dielectric Materials for CMOS Technologies." Doctoral thesis, Uppsala universitet, Fasta tillståndets elektronik, 2004. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-4611.
Full textKirsch, Paul Daniel. "Surface and interfacial chemistry of high-k dielectric and interconnect materials on silicon." Access restricted to users with UT Austin EID Full text (PDF) from UMI/Dissertation Abstracts International, 2001. http://wwwlib.umi.com/cr/utexas/fullcit?p3034557.
Full textArenas, Daniel J. "Devices and materials for THz spectrosopy [sic] GHz CMOS circuits, periodic hole-arrays and high-frequency dielectric materials /." [Gainesville, Fla.] : University of Florida, 2009. http://purl.fcla.edu/fcla/etd/UFE0024735.
Full textRasafar, Hamid 1954. "THE HIGH FREQUENCY AND TEMPERATURE DEPENDENCE OF DIELECTRIC PROPERTIES OF PRINTED CIRCUIT BOARD MATERIALS." Thesis, The University of Arizona, 1987. http://hdl.handle.net/10150/276509.
Full textWang, Lin. "High-κ dielectric constant oxide and metal gate materials for future CMOS integrated circuits." Thesis, University of Cambridge, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.608646.
Full textReddy, Raj. "A study of high-K dielectric materials in conjunction with a multilayer thick-film system." Thesis, Virginia Tech, 1988. http://hdl.handle.net/10919/43280.
Full textMaster of Science
Umeda, Yuji. "Rational design of dielectric oxide materials through first-principles calculations and machine-learning technique." Doctoral thesis, Kyoto University, 2020. http://hdl.handle.net/2433/245844.
Full text0048
新制・課程博士
博士(工学)
甲第22159号
工博第4663号
新制||工||1727(附属図書館)
京都大学大学院工学研究科材料工学専攻
(主査)教授 田中 功, 教授 中村 裕之, 教授 邑瀬 邦明
学位規則第4条第1項該当
Doctor of Philosophy (Engineering)
Kyoto University
DFAM
Buckingham, David Tracy Willis. "High-Resolution Thermal Expansion and Dielectric Relaxation Measurements on H2O and D2O Ice Ih." Thesis, Montana State University, 2017. http://pqdtopen.proquest.com/#viewpdf?dispub=10607201.
Full textIce Ih, formed by freezing liquid water below 273∼K at atmospheric pressure, is well-known and highly-studied, but some of its fundamental physical properties have mystified scientists since the early twentieth century. The thermal expansion is one of those properties; the low relative-resolution of past measurements has left questions regarding the structural isotropy and negative thermal expansion (NTE). Furthermore, the existence of relaxation phenomena near 100∼K, related to the residual entropy at 0∼K, may reveal itself through subtle features in the thermal expansion and, thus, warrants further investigation. Here we measure the thermal expansion of ultra-pure single crystal ice from 5–265∼K with 106 times higher relative resolution than has previously been made. The data reveal a distinct crossover to NTE below 62∼K, and a third-order transition along the crystallographic \(c\)-axis near 100∼K, as evident by an unambiguous relaxational decrease in the thermal expansion coefficient on cooling. To further understand the nature of the transition, isotopic substitution and dielectric measurements were performed.
Three properties of the dielectric relaxation in ice were probed at temperatures between 80--250∼K; the thermally stimulated depolarization (TSD) current, static electrical conductivity, and dielectric relaxation time. The dielectric data agree with relaxation-based models and provide for the determination of activation energies which identify the dielectric relaxation in ice as being dominated by Bjerrum defects below 140∼K. An anisotropy was also found in the data which revealed that molecular reorientations, in the form of propagating Bjerrum point defects, are energetically favored along the \(c\)-axis between 80--140∼K. Furthermore, a similar relaxational effect to that observed in the thermal expansion was observed in the TSD along \(c\), providing a strong correlation between dielectric relaxation and inherent thermodynamic relaxation in ice. Finally, isotopic substitution in both measurement sets indicates the transition is related the movements of hydrogen nuclei, not those of the whole molecule, and provides details about the low-temperature phonon modes. These findings paint a picture of ice as a proton-disordered crystal which undergoes a partial ordering on cooling near 100∼K but, before an ordered equilibrium state is realized, the exponentially increasing relaxation time rapidly slows the ordering and ultimately freezes-in the residual entropy, causing a continuous decrease in the thermal expansion coefficient.
Kim, Sunho Ph D. Massachusetts Institute of Technology. "Defect and electrical properties of high-K̳ dielectric Gd₂O₃ for magneto-ionic and memristive memory devices." Thesis, Massachusetts Institute of Technology, 2020. https://hdl.handle.net/1721.1/129007.
Full textCataloged from student-submitted PDF of thesis. The "K̳̳" in title on title page appeared as subscript "K."
Includes bibliographical references (pages 127-134).
While high-[subscript K] dielectrics utilized in CMOS technology are noted for their highly insulating characteristics, they have demonstrated surprising electrolytic behavior as key components in a variety of thin film memory devices, including those based on magneto-ionic and memristive behavior. In this work, we focus on the rare earth sesquioxide, Gd₂O₃, a well-known high-κ dielectric that has exhibited a variety of electrolytic properties during the development and operation of the first magneto-ionic devices developed at MIT. Specifically, we focused our investigation on the defect chemistry and electrical properties of Gd₂O₃ in order to better understand the relationship between the structure, chemistry, processing conditions, and operating environment and the material's low-temperature ionic and electronic transport properties and the means for their optimization vis-à-vis memory device operation.
Phase (monoclinic and cubic) and dopant controlled (Ca, Ce, Sr, Zr) polycrystalline pellets of 8 different Gd₂O₃ systems were prepared to investigate various defect regimes in consideration of this material's polymorphism. We considered intrinsic anion-Frenkel disorder and electronic disorder, equilibration with the gas phase, water incorporation, and dopant incorporation in the defect modeling, taking into account the roles of crystallographic structure as well as oxygen ion defect and protonic generation. The primary method utilized to characterize the defect chemistry and transport properties of Gd₂O₃ was the analysis of the dopant, p0₂ and temperature dependencies of the electrical conductivity extracted from complex impedance spectra obtained over the p0₂ range of 1 to 10⁻¹⁵ atm, for 5 isotherms between 700 and 900 °C with 50 °C steps and for a range of acceptor and donor dopants.
Based on the p0₂ dependency of conductivities, in light of the defect modeling, the majority point defects in each system were identified. Electronic and ionic migration energies and thermodynamic parameters were extracted via the defect modeling and temperature dependencies of conductivities. In nearly all cases, the predominant charge carrier under oxidizing conditions at elevated temperatures was identified as the p-type electron-hole, largely due to oxygen excess non-stoichiometry in these systems. With decreasing p0₂, transport tended to switch from semiconducting towards ionic. Depending on phase, dopant type & concentration, temperature, and relative humidity, the predominant ionic conductivity was found to be via oxygen interstitials, oxygen vacancies, and/or protons, the latter given by the propensity of Gd₂O₃ to take up water in solid solution from the environment by the formation of OH[superscript .]species.
Unexpectedly, the ionic mobilities of defects in the denser and less symmetric monoclinic system exhibited higher ionic mobilities than the more open bixbyite structure. The hole electronic species in the investigated systems were found to migrate via the small polaron hopping mechanism with rather large hopping energies. This resulted in an inversion of hole and proton mobility magnitudes at reduced temperatures in the monoclinic system. Extrapolation of ionic and electronic defect conductivities to near room temperature, based on our derived defect and transport models, was not able to explain, on its own, the observed electrolytic properties of the Gd₂O₃ thin films utilized in magneto-ionic devices.
In an attempt to connect the transport properties obtained under equilibrium conditions at elevated temperatures with the behavior of Gd₂O₃ near room temperature, selected thin films Gd₂O₃, prepared by pulsed laser deposition or sputtering, were investigated by complex impedance spectroscopy over the temperature range of 20 - 170°C. While films prepared under dry conditions were indeed found to be highly electrically insulating, films exposed to water vapor exhibited dramatically higher proton conductivities (more than ~10⁸ x) than values extrapolated from high temperature. Parallel thermogravimetric analysis on Gd₂O₃ powder specimens, as a function of temperature, under high humidity conditions, demonstrated a correlation between uptake/loss of incorporated water and conductivity upon cooling and heating, respectively.
We can therefore conclude that the large disconnect between the electrical and electrolytic properties observed between high-κ dielectrics used in CMOS devices such as Gd₂O₃, and their much more highly conductive counterparts used in thin film memory devices, depends strategically on the thin film processing conditions. High-κ dielectrics are fabricated in carefully controlled environments with low relative humidity, while research on, for example, Gd₂O₃ - based magneto-ionic memory devices, is performed under ambient laboratory conditions, where significant water uptake becomes possible at surfaces and grain boundaries. The results and insights obtained in this study can be expected to be applied in achieving further progress in the understanding and optimization of magneto-ionic, memristive, and other devices that rely on proton gating.
by Sunho Kim.
Ph. D.
Ph.D. Massachusetts Institute of Technology, Department of Materials Science and Engineering
Wang, Chunlai. "AZADIPYRROMETHENE-BASED N-TYPE ORGANIC SEMICONDUCTORS AND HIGH DIELECTRIC CONSTANT POLYMERS FOR ELECTRONIC APPLICATIONS." Case Western Reserve University School of Graduate Studies / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=case156708229609051.
Full textSreenivasan, Raghavasimhan. "Metal-gate/high-k dielectric stack engineering by atomic layer deposition : materials issues and electrical properties /." May be available electronically:, 2007. http://proquest.umi.com/login?COPT=REJTPTU1MTUmSU5UPTAmVkVSPTI=&clientId=12498.
Full textKowalski, Benjamin A. "THERMAL EFFECTS ON PROCESSING-STRUCTURE-PROPERTY RELATIONSHIPS IN HIGH TEMPERATURE PIEZOELECTRICS." Case Western Reserve University School of Graduate Studies / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=case1490099155300433.
Full textKim, Yun Sang. "Ferroelectric nanocomposite and polar hybrid sol-gel materials for efficient, high energy density capacitors." Diss., Georgia Institute of Technology, 2014. http://hdl.handle.net/1853/51816.
Full textWei, Daming. "Study of high dielectric constant oxides on GaN for metal oxide semiconductor devices." Diss., Kansas State University, 2014. http://hdl.handle.net/2097/17393.
Full textDepartment of Chemical Engineering
James H. Edgar
Gallium nitride is a promising semiconductor for fabricating field effect transistors for power electronics because of its unique physical properties of wide energy band gap, high electron saturation velocity, high breakdown field and high thermal conductivity. However, these devices are extremely sensitive to the gate leakage current which reduces the breakdown voltage and the power-added efficiency and increases the noise figures. To solve this problem, employing a gate dielectric is crucial to the fabrication of metal insulator semiconductor high electron mobility transistors (MISHEMTs), to reduce the leakage current and increase the magnitude of voltage swings possible. For this device to be successful, imperfections at the oxide-semiconductor interface must be suppressed to maintain the high electron mobility of the device. This research explored multiple high dielectric constant gate oxides (Al[subscript]2O[subscript]3, TiO[subscript]2, and Ga[subscript]2O[subscript]3), deposited on different crystalline orientations and polarities of GaN by atomic layer deposition (ALD) to form metal oxide semiconductor capacitors, including effects of pretreatment on N-polar GaN, ALD TiO[subscript]2/Al[subscript]2O[subscript]3 nano-laminate on thermal oxidized Ga-polar GaN and ALD Al[subscript]2O[subscript]3 on [Italic]c- and [Italic]m-plane GaN Surface pretreatments were shown to greatly alter the morphology of reactive N-polar GaN which is detrimental to the electrical properties. 14 nm thick ALD Al[subscript]2O[subscript]3 films were directly deposited on N-polar GaN without thermal or chemical pretreatments which yield a smooth surface (RMS=0.23 nm), low leakage current (2.09 x 10[superscript]-[superscript]8 A/cm[superscript]2) and good Al[subscript]2O[subscript]3/GaN interface quality, as indicated by the low electron trap density (2.47 x 10[superscript]10 cm[superscript]-[superscript]2eV[superscript]-[superscript]1). In the nano-laminate study, a high dielectric constant of 12.5 was achieved by integrating a TiO[subscript]2/Al[subscript]2O[subscript]3/Ga[subscript]2O[subscript]3 oxide stack layer, while maintaining a low interface trap density and low leakage current. There was a strong correlation between the surface morphology and electrical properties of the device discovered from comparing the ALD Al[subscript]2O[subscript]3 on [Italic]c- and [Italic]m-plane GaN, namely smooth surface lead to small hysteresis. These results indicate the promising potential of incorporation gate dielectric for future GaN devices.
Di, Geronimo Camacho Elizabeth Carolina. "Synthesis, high-pressure study and dielectric characterization of two lead-free perovskite materials : SrTi1-xZrxO3 and KNb1-xTaxO3." Thesis, Montpellier, 2016. http://www.theses.fr/2016MONTT208/document.
Full textPerovskite materials whose general chemical formula is ABO3 are one of the most study ferroelectrics due to the interesting properties that they have for technological applications. However, their properties are directly related to structural phase transitions that could depend of temperature, composition and pressure. In the studies presented here, we first examined the high-pressure behavior of two perovskite materials SrTi1-xZrxO3 (STZ) and KNb1-XTaXO3 (KNT), and we later continued to investigate different sintering techniques in order to improve the densification, dielectric and ferroelectric properties of K(Nb0.40Ta0.60)O3 and (KxNa1-x)Nb0.6Ta0.4O3 ceramics.High-pressure Raman scattering and X-ray diffraction investigations of SrTi1-xZrxO3 (x= 0.3, 0.4, 0.5, 0.6, 0.7) and KNb1-XTaXO3 (x=0.4, 0.5, 0.6, 0.9) powders were conducted in diamond anvil cells. Raman scattering experiments showed and increased of Raman modes with pressure for the STZ samples, which indicates that pressure induced phase transitions towards lower symmetry for these compounds.Moreover, high pressure Raman spectroscopy experiments showed a decrease of the Raman modes as the pressure was increased for the KNT samples, showing that pressure induced phase transitions towards higher symmetries. The evolution of the main Raman modes for the orthorhombic and tetragonal phases were followed until the cubic phase was reach, and allowed us to propose a pressure-composition phase diagram for the KNT compounds.Three different sintering techniques, sintered aids, two step sintering and spark plasma sintering, were used on K(Nb0.4Ta0.6)O3 and (KxNa1-x)Nb0.6Ta0.4O3 ceramics. The use of KF as sintered aid and the two step sintering method showed an improvement of the dielectric constant and dielectric losses of these samples. SPS samples presented a fine microstructure with the highest density and the best ferroelectric behavior. We did not detect any changes on the Curie temperature due the amount of Na but and increase of the dielectric constant and the ferroelectric properties was observed due to the amount of Na
Chakraborti, Parthasarathi. "Nanoscale electrode and dielectric materials, processes and interfaces to form thin-film tantalum capacitors for high-frequency applications." Diss., Georgia Institute of Technology, 2016. http://hdl.handle.net/1853/55010.
Full textBaristiran, Kaynak Canan [Verfasser], and Bernd [Akademischer Betreuer] Tillack. "Characterization of Perovskite-like High k Dielectric Materials for Metal-Insulator-Metal Capacitors / Canan Baristiran Kaynak. Betreuer: Bernd Tillack." Berlin : Universitätsbibliothek der Technischen Universität Berlin, 2013. http://d-nb.info/1031280227/34.
Full textMoradi, Bahareh. "High dielectric permittivity materials in the development of resonators suitable for metamaterial and passive filter devices at microwave frequencies." Doctoral thesis, Universitat Autònoma de Barcelona, 2016. http://hdl.handle.net/10803/384854.
Full textMetamaterials (MTMs) represent an exciting emerging research area that promises to bring about important technological and scientific advancement in various areas such as telecommunication, radar, microelectronic, and medical imaging. The amount of research on this MTMs area has grown extremely quickly in this time. MTM structure are able to sustain strong sub-wavelength electromagnetic resonance and thus potentially applicable for component miniaturization. Miniaturization, optimization of device performance through elimination of spurious frequencies, and possibility to control filter bandwidth over wide margins are challenges of present and future communication devices. This thesis is focused on the study of both interesting subject (MTMs and miniaturization) which is new miniaturization strategies for MTMs component. Since, the dielectric resonators (DR) are new type of MTMs distinguished by small dissipative losses as well as convenient conjugation with external structures; they are suitable choice for development process. The primary advantage in using a high dielectric constant as a DR is to miniaturize the filter size. The size of DR filter is considerably smaller than the dimension of waveguide filters operate at the same frequency. For a given dielectric constant, both resonant frequency and Q-factor are defined according to the dielectric resonator dimensions. That, the higher the dielectric constant, the smaller the space within which the fields are concentrated, the lower the dimension at a defined frequency. To obtain the required compact sizes new stop-band filter is proposed in this work based on number of thick film high dielectric constant epoxy paste (TFDR) as DRs which excited with a microstrip line. In addition, a band-pass filter is proposed based on embedded dielectric resonators (EDR) constitutes a new approach to the miniaturized resonators suitable for metamaterials design without the Q degradation inherent to the coupling coefficient based on sub-wavelength particles. Also this thesis is proposed a new band-pass filter based on split ring resonators (SRRs), which is a one of the popular MTMs building blocks today. The band-pass filters based on this concept can be very promising for the applications where miniaturization and compatibility with planar millimeter wave technology are the important issues. Also, for further miniaturization, embedded DR technology is reported. Another approach for size reduction is modifying the traditional resonator to generate additional modes, which make the resonator to behave as a multimode resonator. Finally a compact ultra-wide band-pass (UWB) band-pass filter using grounded open ring resonator as a multimode resonator (MMR) is proposed. The approach allows using five resonances to produce a 128% fractional bandwidth into the ultra-wide band. A general theoretic framework has been established using transmission matrix description of the filter constituent components. To demonstrate and validate designs functionality, all the proposed devices are implemented and fabricated, which a good agreement between simulations and measurement are obtained. Through these methods it is demonstrated that their equivalent circuit models provide an accurate description of the considered structures. Indeed, a clear relationship between their equivalents circuit model and the layout physical dimensions were found.
Xia, Zhanbo. "Materials and Device Engineering for High Performance β-Ga2O3-based Electronics." The Ohio State University, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=osu1587688595358557.
Full textUppal, Hasan Javed. "Nanoscale performance, degradation and defect analysis of mos devices using high-k dielectric materials as gate stacks by atomic force microscopy." Thesis, University of Manchester, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.509394.
Full textSouza, de Almeida Jailton. "Designing and Tuning the Properties of Materials by Quantum Mechanical Calculations." Doctoral thesis, Uppsala : Acta Universitatis Upsaliensis, 2006. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-6923.
Full textVaidya, Manushka. "Steering Electromagnetic Fields in MRI| Investigating Radiofrequency Field Interactions with Endogenous and External Dielectric Materials for Improved Coil Performance at High Field." Thesis, New York University, 2017. http://pqdtopen.proquest.com/#viewpdf?dispub=10261392.
Full textAlthough 1.5 and 3 Tesla (T) magnetic resonance (MR) systems remain the clinical standard, the number of 7 T MR systems has increased over the past decade because of the promise of higher signal-to-noise ratio (SNR), which can translate to images with higher resolution, improved image quality and faster acquisition times. However, there are a number of technical challenges that have prevented exploiting the full potential of ultra-high field (≥ 7 T) MR imaging (MRI), such as the inhomogeneous distribution of the radiofrequency (RF) electromagnetic field and specific energy absorption rate (SAR), which can compromise image quality and patient safety.
To better understand the origin of these issues, we first investigated the dependence of the spatial distribution of the magnetic field associated with a surface RF coil on the operating frequency and electrical properties of the sample. Our results demonstrated that the asymmetries between the transmit (B1+) and receive (B 1–) circularly polarized components of the magnetic field, which are in part responsible for RF inhomogeneity, depend on the electric conductivity of the sample. On the other hand, when sample conductivity is low, a high relative permittivity can result in an inhomogeneous RF field distribution, due to significant constructive and destructive interference patterns between forward and reflected propagating magnetic field within the sample.
We then investigated the use of high permittivity materials (HPMs) as a method to alter the field distribution and improve transmit and receive coil performance in MRI. We showed that HPM placed at a distance from an RF loop coil can passively shape the field within the sample. Our results showed improvement in transmit and receive sensitivity overlap, extension of coil field-of-view, and enhancement in transmit/receive efficiency. We demonstrated the utility of this concept by employing HPM to improve performance of an existing commercial head coil for the inferior regions of the brain, where the specific coil’s imaging efficiency was inherently poor. Results showed a gain in SNR, while the maximum local and head SAR values remained below the prescribed limits. We showed that increasing coil performance with HPM could improve detection of functional MR activation during a motor-based task for whole brain fMRI.
Finally, to gain an intuitive understanding of how HPM improves coil performance, we investigated how HPM separately affects signal and noise sensitivity to improve SNR. For this purpose, we employed a theoretical model based on dyadic Green’s functions to compare the characteristics of current patterns, i.e. the optimal spatial distribution of coil conductors, that would either maximize SNR (ideal current patterns), maximize signal reception (signal-only optimal current patterns), or minimize sample noise (dark mode current patterns). Our results demonstrated that the presence of a lossless HPM changed the relative balance of signal-only optimal and dark mode current patterns. For a given relative permittivity, increasing the thickness of the HPM altered the magnitude of the currents required to optimize signal sensitivity at the voxel of interest as well as decreased the net electric field in the sample, which is associated, via reciprocity, to the noise received from the sample. Our results also suggested that signal-only current patterns could be used to identify HPM configurations that lead to high SNR gain for RF coil arrays. We anticipate that physical insights from this work could be utilized to build the next generation of high performing RF coils integrated with HPM.
Wu, Dongping. "Novel concepts for advanced CMOS : Materials, process and device architecture." Doctoral thesis, KTH, Microelectronics and Information Technology, IMIT, 2004. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3805.
Full textThe continuous and aggressive dimensional miniaturization ofthe conventional complementary-metal-oxide semiconductor (CMOS)architecture has been the main impetus for the vast growth ofIC industry over the past decades. As the CMOS downscalingapproaches the fundamental limits, unconventional materials andnovel device architectures are required in order to guaranteethe ultimate scaling in device dimensions and maintain theperformance gain expected from the scaling. This thesisinvestigates both unconventional materials for the gate stackand the channel and a novel notched-gate device architecture,with the emphasis on the challenging issues in processintegration.
High-κ gate dielectrics will become indispensable forCMOS technology beyond the 65-nm technology node in order toachieve a small equivalent oxide thickness (EOT) whilemaintaining a low gate leakage current. HfO2and Al2O3as well as their mixtures are investigated assubstitutes for the traditionally used SiO2in our MOS transistors. These high-κ filmsare deposited by means of atomic layer deposition (ALD) for anexcellent control of film composition, thickness, uniformityand conformality. Surface treatments prior to ALD are found tohave a crucial influence on the growth of the high-κdielectrics and the performance of the resultant transistors.Alternative gate materials such as TiN and poly-SiGe are alsostudied. The challenging issues encountered in processintegration of the TiN or poly-SiGe with the high-k are furtherelaborated. Transistors with TiN or poly-SiGe/high-k gate stackare successfully fabricated and characterized. Furthermore,proof-of-concept strained-SiGe surface-channel pMOSFETs withALD high-κ dielectrics are demonstrated. The pMOSFETs witha strained SiGe channel exhibit a higher hole mobility than theuniversal hole mobility in Si. A new procedure for extractionof carrier mobility in the presence of a high density ofinterface states found in MOSFETs with high-κ dielectricsis developed.
A notched-gate architecture aiming at reducing the parasiticcapacitance of a MOSFET is studied. The notched gate is usuallyreferred to as a local thickness increase of the gatedielectric at the feet of the gate above the source/drainextensions. Two-dimensional simulations are carried out toinvestigate the influence of the notched gate on the static anddynamic characteristics of MOSFETs. MOSFETs with optimizednotch profile exhibit a substantial enhancement in the dynamiccharacteristics with a negligible effect on the staticcharacteristics. Notched-gate MOSFETs are also experimentallyimplemented with the integration of a high-κ gatedielectric and a poly-SiGe/TiN bi-layer gate electrode.
Key words:CMOS technology, MOSFET, high-κ, gatedielectric, ALD, surface pre-treatment, metal gate, poly-SiGe,strained SiGe, surface-channel, buried-channel, notchedgate.
Joyce, Donna Marie. "The Development of DNA-Based Bio-Polymer Hybrid Thin Films for Capacitor Applications." University of Dayton / OhioLINK, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1389285491.
Full textGuffond, Raphaël. "Characterization and modeling of microstructure evolution of cable insulation system under high continuous electric field." Thesis, Sorbonne université, 2018. http://www.theses.fr/2018SORUS039/document.
Full textThis thesis presents a research work on understanding and modeling the electrical behavior of insulation system in cables subjected to high DC constraints. Electrical properties of polymeric insulation are directly related to their chemical and physical heterogeneities present at several scales. In this work, a new model is developed to simulate the modification over time of the microstructure in insulation polymers under electric field and temperature as well as the subsequent impacts on electrical properties. In this model, matrices are used to describe the distribution of each heterogeneity and electrical property in semi-crystalline polymer. When stressed under electric field and at temperature, matrices of microstructure evolve from implemented genetic laws. This simulated microstructure evolution yields to the simulation of electrical property changes over time at transient and steady state. To define these genetic laws, a detailed characterization of the physical, chemical and electrical properties of specific materials as a function of temperature and electric field is experimentally performed. Genetic laws are notably implemented to take into account the impact of the semi-crystalline structure and the presence of chemical residues in polymer electrical properties. Based on these genetic evolution laws, this modeling approach allows simulating DC electrical behavior of polymers only from their physical and chemical characterizations and reproduce accurately experimental electrical behavior with a faster solving time compared to other simulation methods
Guiraud, Alexandre. "Intégration de matériaux à forte permittivité diélectrique dans les mémoires non volatile avancées." Thesis, Aix-Marseille, 2012. http://www.theses.fr/2012AIXM4763/document.
Full textThe work of this thesis is on integration of high dielectric constant materials (High-k) as dielectric interpoly in Flash non volatile memories. The objective is to determine which High-k materials are suitable as interpoly dielectric in place of the ONO stack currently used. A range of High-k materials have been studied by electrical characterizations (I-V, C-V, breakdown statistics…) and physical characterizations (TEM, EDX, XPS…) in order to select those with the best properties for an interpoly dielectric. The difficulties in integration of High-k materials in a Flash memory process flow have been taken in account and solutions have been proposed
Treufeld, Imre. "I. Polymer Films for High Temperature Capacitor ApplicationsII. Differential Electrochemical Mass Spectrometry." Case Western Reserve University School of Graduate Studies / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=case1465503063.
Full textHossain, Md Tashfin Zayed. "Electrical characteristics of gallium nitride and silicon based metal-oxide-semiconductor (MOS) capacitors." Diss., Kansas State University, 2013. http://hdl.handle.net/2097/16942.
Full textDepartment of Chemical Engineering
James H. Edgar
The integration of high-κ dielectrics with silicon and III-V semiconductors is important due to the need for high speed and high power electronic devices. The purpose of this research was to find the best conditions for fabricating high-κ dielectrics (oxides) on GaN or Si. In particular high-κ oxides can sustain the high breakdown electric field of GaN and utilize the excellent properties of GaN. This research developed an understanding of how process conditions impact the properties of high-κ dielectric on Si and GaN. Thermal and plasma-assisted atomic layer deposition (ALD) was employed to deposit TiO₂ on Si and Al₂O₃ on polar (c-plane) GaN at optimized temperatures of 200°C and 280°C respectively. The semiconductor surface treatment before ALD and the deposition temperature have a strong impact on the dielectric’s electrical properties, surface morphology, stoichiometry, and impurity concentration. Of several etches considered, cleaning the GaN with a piranha etch produced Al₂O₃/GaN MOS capacitors with the best electrical characteristics. The benefits of growing a native oxide of GaN by dry thermal oxidation before depositing the high-κ dielectric was also investigated; oxidizing at 850°C for 30 minutes resulted in the best dielectric-semiconductor interface quality. Interest in nonpolar (m-plane) GaN (due to its lack of strong polarization field) motivated an investigation into the temperature behavior of Al₂O₃/m-plane GaN MOS capacitors. Nonpolar GaN MOS capacitors exhibited a stable flatband voltage across the measured temperature range and demonstrated temperature-stable operation.
Samet, Mariem. "Étude théorique et expérimentale des effets de la polarisation interfaciale dans les spectres diélectrique des matériaux composites multiphasiques." Thesis, Lyon 1, 2015. http://www.theses.fr/2015LYO10134.
Full textThis research is significant in that it not only develops a generalized approach for modeling the electrical properties of multiphase composite materials but also introduces novel experimental applications in the domain of dielectric properties of composite materials. In order to get complete information: numerical simulations, analytical calculations and dielectric measurements by means of Broadband Dielectric Spectroscopy (BDS) were carried out in this study. First, we derived the scaling laws through a systematically study of global dielectric response of composite materials with different morphology and the original contribution of this thesis is to succeed to derive a universal scaling laws for the global dielectric response of composite materials. Based on these scaling laws three achievements are taken place: designing layered polymer materials with high values of permittivity and low dielectric losses, by adjusting the values of conductivity and the volume fraction of the constituent phases. Also, we discover a new discrimination criterion for electrical polarizations at external and internal interfaces: electrode polarization vs. (MWS) interfacial polarization effects in dielectric spectra of materials. This work opens the general perspective of finding discrimination criteria for different types of electrical polarization, which will represent a useful tool in disseminating the nature of different contributions appearing in the dielectric spectra of materials. Based on our analysis, we derive a new formula. This formula is valid for both electrode polarization and interfacial polarization effects. It allows one to determine the conductivity value from the frequency position of the Maxwell-Wagner-Sillars peak. Measurements of the conductivity values of samples without a direct contact are done. An excellent agreement between experiment and calculations is obtained. This results offer the opportunity to develop a new coupled electrical-mechanical approach, by electrical measurements performed during mechanical stretching
Xu, Toby Ge. "Material and array design for CMUT based volumetric intravascular and intracardiac ultrasound imaging." Diss., Georgia Institute of Technology, 2015. http://hdl.handle.net/1853/54861.
Full textZhang, Lanlin. "Fabrication and materials for magneto-photonic assemblies for high-gain antenna applications at GHz frequencies." Columbus, Ohio : Ohio State University, 2008. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1221248675.
Full textGarreau, Jonathan. "Étude de filtres hyperfréquence SIW et hybride-planaire SIW en technologie LTCC." Phd thesis, Université de Bretagne occidentale - Brest, 2012. http://tel.archives-ouvertes.fr/tel-00858068.
Full text"Mechanisms of Microwave Loss Tangent in High Performance Dielectric Materials." Doctoral diss., 2013. http://hdl.handle.net/2286/R.I.16430.
Full textDissertation/Thesis
Ph.D. Materials Science and Engineering 2013
Jhih-YongChen and 陳智勇. "Development and Applications of High QMicrowave Dielectric Materials." Thesis, 2010. http://ndltd.ncl.edu.tw/handle/11648845896633681786.
Full text國立成功大學
電機工程學系碩博士班
98
Microwave dielectric resonators (DRs) which are fabricated by high dielectric constant, high quality factor, and good temperature stability of microwave dielectric materials are suitably applied in antennas, filters, oscillators, and diplexers. Recently, with the rapidly progress in the microwave communication systems, miniaturization and performance enhancement have become two main requirements of the microwave devices. Therefore, high quality factor dielectric materials can be utilized in designing high-performance microwave devices in communication system. Moreover, the integration of dielectric materials is also main method to carry out the miniaturization of microwave devices. In addition, to develop microwave dielectric materials, lower sintering temperatures plays an important role in the future. As mentioned above, the main study of this dissertation is divided five parts which preparation of high dielectric constant, high quality factor, low sintering temperature microwave dielectric materials, fabrication of high quality Mg4Ta2O9 dielectric thin films and their applications on microstrip bandpass filters. 1.Development of High Q Microwave Dielectric Materials [a]Study of Mg2TiO4 Ceramics: (1)Binary titanate ceramic Mg2TiO4 ( ~ 14, Q×f ~ 150,000 GHz, and τf ~ –50 ppm/°C), having extremely high quality factor, were reported as promising dielectric ceramics for microwave applications. Their low cost even brought much more attention. In fact, they have already been used as dielectric materials for GPS antennas and wireless LAN filters. Therefore, the spinel-structured Mg2TiO4 is worthy to investigate its microwave properties. In this dissertation, with partial replacement of Mg by Co or Ti by Sn, the Q×f of the dielectrics (Mg0.95Co0.05)2TiO4 ( ~ 15.7, Q×f ~ 286,000 GHz, and τf ~ –52.5 ppm/°C) and Mg2(Ti0.95Sn0.05)O4 ( ~ 15.57, Q×f ~ 318,000 GHz, and τf ~ –45.1 ppm/°C) can be easily boosted to a value higher than 250,000 GHz and retain compatible and τf. (2)In order to achieve temperature-stable materials, CaTiO3, Ca0.61Nd0.26TiO3, Ca0.6La0.8/3TiO3, Ca0.8Sm0.4/3TiO3, and Ca0.8Sr0.2TiO3 were added to (Mg0.95Co0.05)2TiO4 and Mg2(Ti0.95Sn0.05)O4 ceramics, respectively. Addition of compensators, having much smaller grain sizes in comparison with that of (Mg0.95Co0.05)2TiO4 and Mg2(Ti0.95Sn0.05)O4, could effectively hold back abnormal grain growth in the (Mg0.95Co0.05)2TiO4 and Mg2(Ti0.95Sn0.05)O4 matrixes. Hence, using the compensators can effectively lower the sintering temperature of the ceramic bulks. Dielectric characteristics and sintering behavior of these ceramic systems were investigated. A two-phase system, which was confirmed by the XRD patterns and the EDX analysis. Moreover, the microstructures of the sintered bulks were characterized by SEM. (3)As mentioned above, the optimal microwave dielectric properties are achieved in 0.92(Mg0.95Co0.05)2TiO4–0.08Ca0.8Sr0.2TiO3 ceramics sintered at 1300°C for 4 h with a dielectric constant ( ) value of 19.22, a quality factor (Q×f) value of 123,200 GHz, and a temperature coefficient of resonant frequency (τf) value of 2.8 ppm/°C. Furthermore, in order to lower the sintering temperature, sintering aid such as B2O3 was used to produce the liquid phase that degrades the sintering temperatures. The microstructures and the microwave dielectric properties with B2O3 additions were investigated. [b] Study of ZnX2O6 (X = Nb and Ta) Ceramics: (1)Partial Replacement of ZnNb2O6 Ceramics The effects of substituting Nb5+ with Ta5+ on the microwave dielectric properties of the ZnNb2O6 ceramics were investigated in this dissertation. The forming of Zn(Nb1-xTax)2O6 (x = 0–0.09) solid solution was confirmed by the measured lattice parameters and the EDX analysis. A fine combination of microwave dielectric properties ( ~ 24.57, Q×f ~ 152,000 GHz, and τf ~ –71.1 ppm/°C) was achieved for Zn(Nb0.95Ta0.05)2O6 solid solution sintered at 1175°C for 2 h. (2)Partial Replacement of ZnTa2O6 Ceramics ZnTa2O6 microwave dielectric materials have been developed as the microwave dielectric resonators in the past, because the dielectric resonators fabricated by ZnTa2O6 ceramics reveal the excellent microwave dielectric properties. However, the quality factor of ZnTa2O6 ceramic is still not good enough for the applications at the microwave frequency. In order to improve the microwave dielectric properties, with the partial replacement of ZnTa2O6 ceramics were investigated. The forming of (Zn0.95M2+0.05)Ta2O6 (M2+ = Co, Mn, Mg, and Ni) and Zn(Ta0.95Nb0.05)2O6 solid solutions were confirmed by the XRD patterns, HR-TEM lattice images, and the EDS analysis. 2.Research of High K Microwave Dielectric Materials Several complex perovskites ceramics A(B2+0.5B4+0.5)O3 (where A = La, Nd, and Sm; B2+ = Mg, Zn, and Co; B4+ = Ti and Sn) have been reported due to their excellent microwave dielectric properties. Among them, La(Mg0.5Ti0.5)O3 has a high dielectric constant ( ~ 29), a high quality factor (Q×f value ~ 75,500 GHz), and a large negative temperature coefficient of resonant frequency (τf ~ –65 ppm/°C). In order to compensate the negative τf of the La(Mg0.5Ti0.5)O3 ceramics, Ca0.8Sm0.4/3TiO3 and Ca0.8Sr0.2TiO3 perovskite which have positive τf had been added. The experiment result showed that 0.5La(Mg0.5Ti0.5)O3–0.5Ca0.8Sr0.2TiO3 have the best microwave dielectric properties, it’s ~ 47.12, Q×f ~ 35,000 GHz, and τf ~ –4.7 ppm/°C. In addition, the X-ray diffraction (XRD) patterning and scanning electron microscopy (SEM) analysis were also employed to study the crystal structures and microstructures of the ceramics. 3.Investigation of Low-Temperature Sintering Microwave Dielectrics Using CuO-Doped Zn(Nb0.95Ta0.05)2O6 Ceramics The influence of CuO additions on the sintering behavior and microwave dielectric properties of Zn(Nb0.95Ta0.05)2O6 ceramic and its chemical compatibility with Ag have been investigated. The CuO additions not only effectively lower the sintering temperature of Zn(Nb0.95Ta0.05)2O6 ceramics to 930°C, the optimized sintering temperatures also decrease with increasing CuO contents due to the liquid phase effect. The Q×f value is a function of the sintering temperature and the amount of CuO addition. With 4.5 wt% CuO addition, it varies from 8,500 to 77,200 GHz as the sintering temperature increases from 840°C to 930°C for 2 h. For low-firing multilayer applications, a combination of dielectric properties with an ~ 22.87, a Q×f ~ 77,200 GHz, and a τf ~ –70.8 ppm/°C can be achieved for 4.5 wt% CuO-doped Zn(Nb0.95Ta0.05)2O6 ceramic sintered at 930°C for 2 h. 4.Fabrication and Characteristics of Mg4Ta2O9 Dielectric Thin Films by RF Magnetron Sputtering Recently, high permittivity dielectric films with low leakage current and high break-down voltage are of the great importance for a variety of integrated devices, such as storage capacitors in dynamic random access memory (DRAM). In this dissertation, the Mg4Ta2O9 target was prepared and used for deposition. The crystal structure and surface morphology of the films affected by deposition conditions, such as RF power and sputtering time. The physical and electrical characteristics of the thin films were investigated. 5.Design and Fabrication of Microstrip Bandpass Filters The microstrip bandpass filters of SIR with a (skew-symmetric) feed structure and open-stubs are presented. In this dissertation, using high permittivity ceramic substrates to miniaturize the sizes of Butterworth bandpass filters are investigated. The selectivity and stopband rejction of the designed filters can be improved significantly by utilizing the feed structure and open-stubs. The responses of the bandpass filters using Al2O3 ( = 9.8, = 0.0005, 1.6-mm thickness), and 0.92(Mg0.95Co0.05)2TiO4–0.08Ca0.8Sr0.2TiO3 with 0.5 wt% B2O3 addition ( = 18.07, = 0.0001, 1.6-mm thickness) ceramic substrates are designed at a center frequency of 2.4 GHz. The compact size and high-performance of the filter are presented in this thesis.