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Chua, L. L. "Organic field-effect transistors." Thesis, University of Cambridge, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.597679.
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In this thesis, we demonstrated that divinyltetramethyldisiloxane-benzocyclobutene (BCB), which has previously been used as an isolation dielectric in III-IV semiconductor devices, in fact makes an excellent gate dielectric material in OFETs after suitable purification. Robust ultra-thin films with high glass transition temperature and high dielectric breakdown strength can be obtained by simple spin-coating followed by rapid-thermal-anneal to above 250°C. With this material, we were able to demonstrate remarkable performance in polymer OFETs and explore several aspects of their physics. In Chapter 2, we introduce the use of BCB as a good candidate for solution-processable organic gate dielectric. Pinhole-free ultra-thin gate dielectric film as thin as 50nm can be made from this material. With this gate dielectric, robust continual cyclic operation of poly[(9,9-dioctylfluorene-2,7-diyl)-alt-(phenylene-(N-(p-2-butylphenyl-imino-phenylene)) (TFB) FETs at 120°C was achieved. Previously, the thinnest practical solution-processable gate dielectric thickness was >300 nm-thick. In Chapter 3, we demonstrated self-organised polymer semiconductor/dielectric FETs fabricated using a spontaneous and an unusual vertical phase separation of the TFB polymer semiconductor and the BCB dielectric materials during film spinning. This method enables the formation of semiconductor and dielectric layers at the same time without exposing their interface to air. Using these devices, we established that a critical root-mean-square interface roughness of 0.7 nm (measured on the 100 nm length scale) could be tolerated without loss of mobility of the devices, probably related to the hopping of the carries at the interface. In Chapter 4, we demonstrated using this non-trapping BCB dielectric the generality of n-type field-effect conduction across a wide range of polymer organic semiconductors. We showed that this was previously suppressed by interface trapping of the accumulated electrons by the –OH group in the gate dielectrics that have often been used. We found electron mobilities very similar to, if not larger than, hole mobilities across a range of organic semiconductors. Therefore, many (though not all) π-conjugated materials are by their nature ambipolar and can support both electron and hole conduction nearly equally well. Their previous classification into “n-type” and “p-type” materials is thus somewhat arbitrary. Finally, in Chapter 5, we used BCB as the top gate dielectric and fabricated fully functional double-gate OFETs over a bottom gate dielectric. We showed that such devices exhibit electrostatic coupling of the two gates occurs to produce an “AND” logic gate.
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Günther, Alrun Aline. "Vertical Organic Field-Effect Transistors." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-207731.
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Diese Arbeit stellt eine eingehende Studie des sogenannten Vertikalen Organischen Feld-Effekt-Transistors (VOFET) dar, einer neuen Transistor-Geometrie, welche dem stetig wachsenden Bereich der organischen Elektronik entspringt. Dieses neuartige Bauteil hat bereits bewiesen, dass es in der Lage ist, eine der fundamentalen Einschränkungen herkömmlicher organischer Feld-Effekt-Transistoren (OFETs) zu überwinden: Die für Schaltfrequenz und An-Strom wichtige Kanallänge des Transistors kann im VOFET stark reduziert werden, ohne dass teure und komplexe Strukturierungsmethoden genutzt werden müssen. Das genaue Funktionsprinzip des VOFET ist bisher jedoch weitgehend unerforscht. Durch den Vergleich von experimentellen Daten mit Simulationsdaten des erwarteten Bauteil-Verhaltens wird hier ein erstes, grundlegendes Verständnis des VOFETs erarbeitet. Die so gewonnenen Erkenntnisse werden im Folgenden genutzt, um bestimmte Parameter des VOFETs kontrolliert zu manipulieren. So wird beispielsweise gezeigt, dass die Morphologie des organischen Halbleiters, und damit seine Abscheidungsparameter, sowohl für die VOFET-Herstellung als auch für den Ladungsträgertransport im fertigen Bauteil eine wichtige Rolle spielen. Weiterhin wird gezeigt, dass der VOFET, genau wie der konventionelle OFET, durch das Einbringen von Kontaktdotierung deutlich verbessert werden kann. Mit Hilfe dieser Ergebnisse kann gezeigt werden, dass das Funktionsprinzip des VOFETs mit dem eines konventionellen OFETs nahezu identisch ist, wenn man von geringen Abweichungen aufgrund der unterschiedlichen Geometrien absieht. Basierend auf dieser Erkenntnis wird schließlich ein VOFET präsentiert, welcher im Inversionsmodus betrieben werden kann und so die Lücke zur konventionellen MOSFET-Technologie schließt. Dieser Inversions-VOFET stellt folglich einen vielversprechenden Ansatz für leistungsfähige organische Transistoren dar, welche als Grundbausteine für komplexe Elektronikanwendungen auf flexiblen Substraten genutzt werden könnenThis work represents a comprehensive study of the so-called vertical organic field-effect transistor (VOFET), a novel transistor geometry originating from the fast-growing field of organic electronics. This device has already demonstrated its potential to overcome one of the fundamental limitations met in conventional organic transistor architectures (OFETs): In the VOFET, it is possible to reduce the channel length and thus increase On-state current and switching frequency without using expensive and complex structuring methods. Yet the VOFET's operational principles are presently not understood in full detail. By simulating the expected device behaviour and correlating it with experimental findings, a basic understanding of the charge transport in VOFETs is established and this knowledge is subsequently applied in order to manipulate certain parameters and materials in the VOFET. In particular, it is found that the morphology, and thus the deposition parameters, of the organic semiconductor play an important role, both for a successful VOFET fabrication and for the charge transport in the finished device. Furthermore, it is shown that VOFETs, just like their conventional counterparts, are greatly improved by the application of contact doping. This result, in turn, is used to demonstrate that the VOFET essentially works in almost exactly the same way as a conventional OFET, with only minor changes due to the altered contact arrangement. Working from this realisation, a vertical organic transistor is developed which operates in the inversion regime, thus closing the gap to conventional MOSFET technology and providing a truly promising candidate for high-performance organic transistors as the building blocks for advanced, flexible electronics applications
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Mohammad, Ahmed Fareed. "Polyelectrolyte based organic field effect transistors." Thesis, Linköpings universitet, Institutionen för teknik och naturvetenskap, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-96237.
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In this thesis work, the fabrication of dual gate organic field-effect transistors (DGOFETs) using polyanionic proton conductor named polyvinylphosphonic acid and acrylic acid P(VPA-AA), SiO 2 as gate insulating materials and poly(3-hexylthiophene) (P3HT) as organic semiconductor have been studied. Upon operation, the top insulating layer forms large electric double layer capacitors (EDLCs)at the Ti/P(VPA-AA) and P(VPAAA)/ P3HT interfaces. This new type of robust transistor, called as EDLC-OFET, displays fast response (<0.3 ms), a reasonably high field effect mobility (0.0030 cm² V -1 s-1), a low ION/IOFF ratio (150), and operates at low voltage (<1 V). Results concerning the influence of bottom gate on the DG-OFET are presented and discussed. The results presented are important for low-cost printed polymer electronics. Also, various conducting polymer gate electrode in addition to laminated OFET to form EDLC-OFET have been tested. Conducting polymers include PEDOT:PSS and polyaniline (PANI).
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Ritjareonwattu, Supachai. "Ion sensitive organic field effect transistors." Thesis, Durham University, 2011. http://etheses.dur.ac.uk/3292/.
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Ion sensitive organic field-effect transistors (ISOFETs) with a metal–oxide–semiconductor field-effect transistor (MOSFET) architecture have been fabricated by using poly(3-hexylthiophene) (P3HT) and poly(methyl methacrylate) (PMMA) as the semiconductor and dielectric layers, respectively. To avoid any pin-holes in the dielectric layer, the ISOFET was coated by two separate PMMA layers. An Ag/AgCl double-junction reference electrode was used as the gate. The results show that the uncoated ISOFET exhibited transistor behaviour in aqueous solutions. However, these devices possessed a small sensitivity of about 0.5 nA dec-1 to H+, K+ and Na+ ions. Langmuir-Blodgett membranes were then used to improve the ISOFET response to the target ions in solution. By coating the gate dielectric (PMMA) with an LB membrane of pure arachidic acid (AA), the ISOFETs showed a significantly higher sensitivity to H+ ions of about 3.5 nA pH-1, but no improvement in the pK response (< 0.5 nA dec-1). The compact ionised layers of carboxylic acid head groups were thought to lead to the improvement in the pH sensitivity; however, the layers of long hydrocarbon chains prevented large monovalent ions, such as K+ and Na+, from interacting with the ionised carboxylic acid head groups. ISOFETs coated with an arachidic acid/valinomycin (AA/val) mixture did not show any selectivity to K+ ions, but exhibited enhanced sensitivities to both K+ and Na+ ions. Instead of trapping K+ ions, the valinomycin molecules in the AA membrane were thought to disrupt the membrane architecture and provide ion-leakage channels. Pure valinomycin-coated ISOFETs also revealed enhancements in both sensitivity and selectivity to K+ ions over Na+. This may be due to the fact that the cavity in the valinomycin molecules can accommodate a K+ ion but not a Na+ ion. To study facilitated K+ transport across the membrane, LB films of AA/val mixture and pure valinomycin were coated on porous supports. The responses of both uncoated and coated membranes were similar. After deposition, collapse of the LB film into the pores may provide leakage channels. This probably led to the observed gradual decrease of the potentials across the membranes.
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Liu, Shiyi. "Understanding Doped Organic Field-Effect Transistors." Kent State University / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=kent1574127009556301.
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Wolanin, Piotr Jacek. "Functional organic nanomaterials for field-effect transistors." Thesis, University of Bristol, 2017. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.723471.
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Takshi, Arash. "Organic metal-semiconductor field-effect transistor (OMESFET)." Thesis, University of British Columbia, 2007. http://hdl.handle.net/2429/31531.
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Organic electronics offers the possibility of producing ultra-low-cost and large-area electronics using printing methods. Two challenges limiting the utility of printed electronic circuits are the high operating voltage and the relatively poor performance of printed transistors. It is shown that voltages can be reduced by replacing the capacitive gate used in Organic Field-Effect Transistors (OFETs) with a Schottky contact, creating a thin-film Organic Metal-Semiconductor Field-Effect Transistor (OMESFET). This geometry solves the voltage issue, and promises to be useful in situations where low voltage operation is important, but good performance is not essential. In cases where high voltage is acceptable or required, it is shown that OFET performance can be greatly improved by employing a Schottky contact as a second gate. The relatively thick insulating layer between the gate and the semiconductor in OFETs makes it necessary to employ a large change of gate voltage (~40 V) to control the drain current. In order to reduce the voltage to less than 5 V a very thin (<10 nm) insulating layer and/or high-k dielectric materials can be used, but these solutions are not compatible with current printing technology. Simulations and implementations of OMESFET devices demonstrate low voltage operation (<5 V) and improved sub-threshold swing compared to the OFET. However, these benefits are achieved at the expense of mobility. In order to achieve good performance in an OFET, including threshold voltage, current ratio and output resistance, the semiconductor thickness has to be less than 50 nm, whereas the thickness of a printed semiconductor is typically larger than 200 nm. The addition of a top Schottky contact on the OFET creates a depletion region thereby reducing the effective thickness of the semiconductor, and resulting in enhanced transistor performance. Simulations and experimental results show improvements in the threshold voltage, the current ratio, and the output resistance of a dual gate transistor, when compared to those in an OFET of the same thickness. The transistors introduced in this work demonstrate means of improving the performance of thick-film OFETs and of achieving substantially lower operation voltage in organic transistors.Applied Science, Faculty of
Electrical and Computer Engineering, Department of
Graduate
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Cheng, X. "Organic field-effect transistors via inkjet printing." Thesis, University of Cambridge, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.597572.
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This thesis is concerned with the fabrication process, charge injection, dielectric preparation and downscaling of organic field-effect transistors via inkjet printing. To provide a general guideline of fabricating inkjet-printed short channel transistors, this thesis starts with an improved self-aligned printing (SAP) technique implemented with gold nanoparticle inks which defines a nanometer scale channel between source and drain electrodes. Electron and hole injection and transport in the channel is studied using ambipolar semiconductor F8BT. Contact resistance effects are found to be significantly more pronounced in these short channel devices and the current is limited by insufficient charge injection. Self-assembled monolayers (SAMs) are effectively employed to reduce the contact resistance in the SAP. Next, the systematic control of electron and hole charge injection in top-gate F8BT ambipolar transistor via SAM modification is investigated. Gold electrodes are modified with PFDT and 1DT to reduce contact resistance and improve charge injection. Furthermore, a crosslinked fluoropolymer Cytop (C-Cytop) is adopted as an ultrathin gate dielectric, which is necessary for proper gate control of the accumulation layer in short channel devices. The C-Cytop can be spin-coated in air with uniform thin films, low gate leakage and high dielectric breakdown strength. The yield and stability of C-Cytop devices are remarkable compared to other non-fluorinated polymer dielectrics and less dependent on the underlying semiconductor roughness. In particular high performance in-type transistors are demonstrated using C-Cytop and small-molecule ActivInk N1400 as the semiconductor. Finally, downscaled inkjet-printed nano-channel n-type transistors are demonstrated by printing silver nanoparticle inks with N1400 and C-Cytop in the SAP structure. The printed silver nanoparticles serves as source contact combining with thin C-Cytop layer as gate dielectric.
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Arthur, Joshua N. "Hygroscopic insulator organic field effect transistor sensors." Thesis, Queensland University of Technology, 2022. https://eprints.qut.edu.au/232689/1/Joshua_Arthur_Thesis.pdf.
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Hygroscopic insulator field effect transistors (HIFETs) are organic transistors with promising characteristics for biosensing applications. However, their fundamental sensing mechanisms are not yet fully understood. This thesis explores HIFET sensors through detailed electrical and optical characterisation, providing vital insights into the distinct mechanisms by which HIFETs detect biologically relevant chemicals. Hydrogen peroxide, a by-product of enzymatic reactions, oxidises the organic semiconductor, modulating the output current. Ionic solutions, such as KCl, NaCl and HCl, modulate the current by changing double layer capacitance. These insights are foundational for the continued development of HIFETs as effective multipurpose biosensing platforms.
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Chiu, Yu-Jui. "Wet Organic Field Effect Transistor as DNA sensor." Thesis, Linköping University, The Department of Physics, Chemistry and Biology, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-11761.
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Label-free detection of DNA has been successfully demonstrated on field effect transistor (FET) based devices. Since conducting organic materials was discovered and have attracted more and more research efforts by their profound advantages, this work will focus on utilizing an organic field effect transistor (OFET) as DNA sensor.
An OFET constructed with a transporting fluidic channel, WetOFET, forms a fluid-polymer (active layer) interface where the probe DNA can be introduced. DNA hybridization and non-hybridization after injecting target DNA and non-target DNA were monitored by transistor characteristics. The Hysteresis area of transfer curve increased after DNA hybridization which may be caused by the increasing electrostatic screening induced by the increasing negative charge from target DNA. The different morphology of coating surface could also influence the OFET response.
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Sou, Antony. "Principles of organic field effect transistor circuit design." Thesis, University of Cambridge, 2015. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.708548.
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Zhang, Xiaohong. "Device engineering of organic field-effect transistors toward complementary circuits." Diss., Atlanta, Ga. : Georgia Institute of Technology, 2009. http://hdl.handle.net/1853/28150.
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Thesis (M. S.)--Electrical and Computer Engineering, Georgia Institute of Technology, 2009.Committee Chair: Kippelen, Bernard; Committee Member: Brand, Oliver; Committee Member: Graham, Samuel; Committee Member: Rohatgi, Ajeet; Committee Member: Shen, Shyh-Chiang.
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Toader, Iulia Genoveva. "Electrical and Morphological Characterisation of Organic Field-Effect Transistors." Doctoral thesis, Universitätsbibliothek Chemnitz, 2012. http://nbn-resolving.de/urn:nbn:de:bsz:ch1-qucosa-100403.
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In dieser Arbeit wurden unterschiedliche Moleküle aus der Klasse der Phthalocyanine (Pc) und Pentacen-Materialien als aktive Schichten in organischen Feldeffekttransistoren (OFETs) mittels organischer Molekularstrahldeposition (OMBD) unter Hochvakuumbedingungen aufgedampft. Die elektrische Charakterisierung von Top-Kontakt (TC) und Bottom-Kontakt (BC) OFET-Konfigurationen, die Auskunft über die Ladungsträgermobilität, die Schwellspannung und das Ein/Aus-Verhältnis gibt, wurde sowohl unter Hochvakuum- als auch unter Umgebungsbedingungen an Luft durchgeführt. Für beide OFET-Konfigurationen wurde Gold für die Source- und Drain-Elektroden genutzt. Aussagen über die Morphologie der untersuchten organischen Schichten, die auf Siliziumsubstraten mit einem 100 nm dicken Siliziumdioxyd (SiO2) Gate-Dielektrikum abgeschieden wurden, wurden mittels Rasterelektronenmikroskopie (SEM) und Rasterkraftmikroskopie (AFM) erhalten. Im Vergleich mit den TC OFETs wurde im Bereich des aktiven Kanals in den BC OFETs die Bildung einer höheren Anzahl von Körnern und Korngrenzen gefunden, welche zur Degradation dieser Bauelemente speziell bei Atmosphärenexposition beiträgt.
Es wurden die nachfolgenden fünf Moleküle aus der Klasse der Pc untersucht: Kupferphthalocyanin (CuPc), Fluoriertes Kupferphthalocyanin (F16CuPc), Kobaltphthalocyanin (CoPc), Titanylphthalocyanin (TiOPc), und Lutetium-bis-Phthalocyanin (LuPc2). Diese Moleküle wurden mit dem Ziel ausgewählt, die Performance der OFETs unter vergleichbaren Präparationsbedingungen zu testen, wenn das zentrale Metallatom, die Halbleitereigenschaften oder die molekulare Geometrie geändert werden. Durch die Fluorierung (F16CuPc) wurde eine Änderung im Leitungsverhalten von CuPc von p-Typ zum n-Typ erreicht und in der elektrischen Charakteristik der OFETs nachgewiesen. Diese Resultate wurden ebenfalls mittels Kelvin-Sonden-Kraftmikroskopie (KPFM) erhalten. Der Einfluss der Molekülgeometrie auf die Performance der Bauelemente wurde durch die Änderung der Gestalt der Moleküle von planar (CuPc, F16CuPc, CoPc) zu nicht planaren Einfach- (TiOPc) und nicht planaren Doppeldeckermolekülen (LuPc2) untersucht. Eine höhere OFET-Performance wurde erreicht, wenn planare Pc-Materialien für die Bildung der aktiven Schicht verwendet wurden. Das kann teilweise auf die Morphologie der Pc-Schichten zurückgeführt werden. AFM-Aufnahmen zeigen, dass im Vergleich mit nicht planaren Molekülen größere Körner und deshalb eine geringere Anzahl von Korngrenzen gebildet werden, wenn planare Pc-Moleküle verwendet werden. Für den Fall von TC CuPc OFETs wurde gezeigt, dass die Performance der Bauelemente verbessert werden kann, wenn das Gate-Dielektrikum mit einer selbstorganisierten Monoschicht von n-Octadecyltrichlorosilan modifiziert wird oder wenn das Substrat während der Aufdampfung der CuPc-Schicht auf einer höheren Temperatur gehalten wird.
Für die Klasse der Pentacen-Materialien wurde ein Vergleich zwischen der Performance von BC OFETs, die die kürzlich synthetisierten fluorierten n-Typ Pentacenquinon-Moleküle nutzen, und denen, die die p-Typ Pentacen-Moleküle nutzen, präsentiert.
Das große Erfordernis hochreine Materialien zu verwenden, um eine Degradation der OFETs zu vermeiden, wurde durch Durchführung von Mehrfachmessungen an den OFET-Bauelementen bestätigt. Aus diesen Experimenten lassen sich Informationen bzgl. der Störstellen an der Grenzfläche organische Schicht/SiO2 ableiten. Weiterhin wurde für einige der untersuchten Moleküle die Performance von BC OFETs unter dem Einfluss von unterschiedlichen Gasen gezeigt.
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Yusoff, Rashid Bin Mohd. "Magnetic field effect in organic semiconducting materials and devices." reponame:Repositório Institucional da UFPR, 2011. http://hdl.handle.net/1884/26437.
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Resumo: O presente trabalho consiste transistores híbridos orgânicos/inorgânicos transistores de base permeável usando polianilina sulfonada como um terminal de base. Quatro emissores diferentes foram utilizados neste trabalho: Alq3, Alq3/C60, C60/Alq3 e C60/Alq3/C60. Foi observada uma forte influência de heteroestruturas da base/emissor sobre as características elétricas e magnéticas do transistor. Duas camadas de injecção diferentes foram utilizadas neste trabalho: Ca e V2O5. Os transistores estudados apresentam elétrons como portadores de carga majoritário. A caracterização elétrica foi realizada através medidas de dois e três terminais. A medida de três terminais consiste em dois modos de operação distintos: base comum e emissor comum. Além disso, as características dos transistores magnéticos foram medidas sequencialmente sob duas condições: (a) sem campo magnético externo aplicado (0 mT), e (b) com campo magnético externo aplicado (100 mT). Imagnes da superfície de filmes de polianilina sulfonada sobre silício foram feitas por microscopia de força atômica e microscopia óptica, a fim de verificar a morfologia da base. As influências da espessura da base e de vazios sobre as características de transistores elétricos e magnéticos foram estudadas.
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Marjanovic, Nenad. "Photoresponsive organic field-effect transistors (photOFETs) photodoping in OFETs." Saarbrücken VDM Verlag Dr. Müller, 2006. http://d-nb.info/989371336/04.
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Jarrett, C. P. "Charge transport in solution-processable organic field-effect transistors." Thesis, University of Cambridge, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.605062.
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The ease of processing conjugated polymers in conjunction with their novel optical and electrical properties has attracted great interest from both theoretical and applied perspectives. There has been particular interest in the development of organic transistors for mass produced low speed electronics. In this dissertation, metal-insulator-semiconductor field-effect transistors (MISFETs) are used to study the physical mechanisms of charge transport in solution-processable conjugated polymers and oligomers. The effect of dopants upon the electrical characteristics of MISFET devices is investigated using a soluble polythiophene derivative. By carefully controlling the doping level, the relationship between the conductivity and field-effect mobility is explored as a function of the dopant level. Temperature dependent measurements of the conductivity for various doping levels are presented, which suggest variable range hopping as a viable mechanism for charge transport. Combining these observations with magnetic susceptibility measurements allows the relationship between the conductivity and field-effect mobility to be modelled within the framework of variable range hopping. The applicability of this model to other systems is discussed in terms of impurities and molecular order. Recently solution-processable polyacetylene has been produced with mesogenic end-groups attached to the end of the chains. These materials are designed in an attempt to improve the molecular order in the films. Charge transport is investigated using MISFET devices by comparing results from materials with and without mesogenic end-groups. The molecular order is explored using electron microscopy and absorption spectroscopy of field-induced charges. Charge transport in precursor-route conjugated materials is studied and shown to result in improvements in device characteristics. In particular, the recent development of a precursor-route to pentacene is utilised and the device characteristics are studied as a function of the conversion conditions. The temperature dependence of the charge mobility is studied for this system and for other conjugated materials. The measurements are compared with those of inorganic systems and discussed in terms of the physical differences between inorganic materials and conjugated polymers.
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Leonardi, Francesca <1986>. "Self-Assembled Monolayers (SAMs) in Organic Field-Effect Transistors." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2014. http://amsdottorato.unibo.it/6461/.
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Organic printed electronics is attracting an ever-growing interest in the last decades because of its impressive breakthroughs concerning the chemical design of π-conjugated materials and their processing. This has an impact on novel applications, such as flexible-large-area displays, low- cost printable circuits, plastic solar cells and lab-on-a-chip devices.
The organic field-effect transistor (OFET) relies on a thin film of organic semiconductor that bridges source and drain electrodes. Since its first discovery in the 80s, intensive research activities were deployed in order to control the chemico-physical properties of these electronic devices and consequently their charge. Self-assembled monolayers (SAMs) are a versatile tool for tuning the properties of metallic, semi-conducting, and insulating surfaces. Within this context, OFETs represent reliable instruments for measuring the electrical properties of the SAMs in a Metal/SAM/OS junction.
Our experimental approach, named Charge Injection Organic-Gauge (CIOG), uses OTFT in a charge-injection controlled regime. The CIOG sensitivity has been extensively demonstrated on different homologous self-assembling molecules that differ in either chain length or in anchor/terminal group.
One of the latest applications of organic electronics is the so-called “bio-electronics” that makes use of electronic devices to encompass interests of the medical science, such as biosensors, biotransducers etc…
As a result, thee second part of this thesis deals with the realization of an electronic transducer based on an Organic Field-Effect Transistor operating in aqueous media. Here, the conventional bottom gate/bottom contact configuration is replaced by top gate architecture with the electrolyte that ensures electrical contact between the top gold electrode and the semiconductor layer. This configuration is named Electrolyte-Gated Field-Effect Transistor (EGOFET).
The functionalization of the top electrode is the sensing core of the device allowing the detection of dopamine as well as of protein biomarkers with ultra-low sensitivity.
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Nasrallah, Iyad. "Investigating charge trapping effects in organic field-effect transistors." Thesis, University of Cambridge, 2015. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.709425.
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Ryu, Kyungbum. "Characterization of organic field effect transistors for OLED displays." Thesis, Massachusetts Institute of Technology, 2005. http://hdl.handle.net/1721.1/33853.
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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2005.Includes bibliographical references (p. 49-51).
This thesis explores the characterization of OFETs that will aid the circuit design of OLED pixel drivers. The contact resistance, flat band voltage, and mobility are extracted from top contact and bottom contact transistors with current-voltage (I-V) and low frequency capacitance-voltage (C-V) measurements. Extraction of contact resistance is found to be crucial in characterization of bottom-contact transistors as it obscures mobility extraction. An unambiguous method of extracting flat band voltage is explored and mobility is extracted with minimal assumptions by separation of charge and mobility from C-V measurements. Mobility is found to increase with gate voltage differing significantly from mobility dependence in crystal silicon MOSFETs.
by Kyungbum Ryu.
S.M.
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Lu, Kexin. "Organic semiconductors for self-assembled monolayer field effect transistors." Thesis, University of Manchester, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.559330.
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Molecular self-assembly has recently attracted significant attention for possible application in organic electronic and optoelectronic devices, such as self-assembled monolayer field-effect transistors (SAMFETs) and functional self-assembled integrated circuits. Self-assembly combines the advantages of low temperature solution processability, regio-selective monolayer adsorption and nano-scale control of film thickness. Much progress has been made in improving device performance using self-assembled monolayers (SAMs). However, most SAMFET devices reported to date showed current modulation only with submicrometre channels, with low device yields and poor reproducibility as a result of limited lateral interconnection of the semiconducting layer.In an attempt to address these issues, this thesis presents an investigation of the synthesis and properties of conjugated SAM molecules for use as the charge transporting layer in SAMFETs. Chapter 1 gives a comprehensive introduction to SAM-based surface systems, organic semiconductors and their use in OFETs and SAMFETs. Chapter 2 discusses attempts to design and synthesise p-type conjugated molecules capable of self-assembly on oxide surfaces based on a phenylene-bithiophene semiconducting core. The optical and electrochemical properties, as well as the thermal behaviour of these molecules are studied in detail. This theme is carried over to Chapter 3, which describes the synthesis, chemical and physical characterisation of two families of n-type SAM molecules. These molecules consist of NTCDI cores with hexyl or cyclohexyl chains as end-capping groups. Incorporation of a selection of materials as the active layer in OFETs or SAMFETs to evaluate the charge transport is demonstrated in Chapter 4. Monolayer films based on p-type monochlorosilane-terminated SAM molecules are made using the solution assembly technique and characterised by contact angle and AFM. OFETs made from DH-PTTP by both thermal evaporation and spin coating show high mobilities comparable to the best values reported in the literature. Top-contact SAMFETs show a hole mobility of 1.1 × 10-3 cm2V-1s-1 in air, consistent with those of solution processed DH-PTTP based OFETs. Finally, an overview of the project and some suggestions for future work are presented in Chapter 5.
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Vaklev, Nikolay Lyubomirov. "Organic field-effect transistors with printed dielectrics and semiconductors." Thesis, Imperial College London, 2014. http://hdl.handle.net/10044/1/44879.
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This thesis presents the development of organic field-effect transistors with printed dielectric and semiconductors. The device architecture was bottom-gate bottom-contact. The electrodes were fabricated via standard photolithography. The first milestones were to gravure-coat the dielectric and structure it with photolithography. Dielectric formulations were screened for their ability to photopattern with radical photoinitiators. Variable processing conditions were also investigated such as annealing time and temperature. The preferred formulation and processing conditions gave ca. 130 nm thick dielectric films and 1-2 nm root-mean-square surface roughness. The dielectric films were tested in parallel capacitors and field-effect transistors. For comparison, the dielectric was also spin-cast and processed analogously to the gravure-coated films. Under the same conditions gravure-coating gave films with equal uniformity and insulating properties as spin-casting. Transistors were prepared with thermally-evaporated pentancene and TIPS-pentacene (6,13-bis(triisopropylsilylethynyl) pentacene) via spin- or zone-casting. The measured mobilities were amongst the highest reported in the literature for this material set and device architecture. The highest transistor mobility with TIPS-pentacene was achieved by blending the semiconductor with poly(a-methylstyrene) (PaMS). Device characteristics such as mobility, threshold voltage and sub-threshold swing voltage were calculated and their evolution with blending ratio followed. The semiconductor was either spin-cast onto pre-deposited PaMS layers with different thickness or TIPS-pentacene was blended with PaMS already in the ink. The work concluded with structured gravure-printing of the dielectric and semiconductor. Dielectric inks with different viscosity were printed and print quality investigated. The film thickness ranged between 60 and 500 nm. Exemplary films were used in the fabrication of transistors and complementary inverters. TIPS-pentacene was directly blended with polymer binders and printed.
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PRENTICE, DAVID CHARLES. "SIMULATION OF PENTACENE ORGANIC METAL-OXIDE FIELD EFFECT TRANSISTORS." University of Cincinnati / OhioLINK, 2003. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1060200543.
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Hague, Lee. "The vapour sensing capabilities of organic field-effect transistors." Thesis, University of Sheffield, 2012. http://etheses.whiterose.ac.uk/3196/.
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The work in this doctoral thesis is mainly concerned with the detection of volatile organic vapours (analytes) using organic field-effect transistors (OFETs) as transducers, in some cases using a ‘sensitiser layer’ on top of the devices to improve their response to certain analytes; some work has also been carried out using a gold nano-particle chemi-resistor to detect amine vapour and the development of an aqueous sensing system is also discussed. It was found that the porphyrins PtOEP (platinum (II) octaethyl porphyrin) and PtEP-I (Etioporphyrin-I) could be used as organic semiconductors and that PtOEP was sensitive to isopropanol (IPA) and acetone vapours; PtOEP was also used to successfully sensitise a pentacene OFET to ethylene vapour at low ppm concentrations. Pentacene OFETs were found to be sensitive to octylamine (an amine), ethylethanoate (an ester), formamide (an amide) and ethylene (an alkene); through the use of a 2:1 molar ratio blend of the calixarene calix[8]arene (calixarene 2) and the porphyrin 5,10,15,20-Tetrakis (3,4-bis (2-ethylhexyloxy) phenyl)-21H,23H-porphyrinato cobalt (II) (Co-EHO) as a sensitiser layer, it was possible to introduce sensitivity to both octanal (an aldehyde) and octan-2-one (a ketone) into a pentacene OFET; the calixarene: 5,17-(34-nitrobenzylideneamino)-11,23-di-tert-butyl-25,27-diethoxycarbonyl-methyleneoxy-26,28dihydroxycalix[4]arene (calixarene 1) was also be used to improve OFET recovery after exposure to ethylethanoate and formamide, but some sensor response was lost in the process. The n-type organic semiconductor PDI8-CN2 (N,N’-bis (n-octyl)- dicyanoperylene-3,4:9,10-bis(dicarboximide)) was found to be sensitive to octylamine vapour, but the nature of its response seems to indicate some kind of amine base-doping mechanism is at work within the device, analogous to the acid doping possible with p-type semiconductors. Gold nano-particles were found to be sensitive to octylamine vapour as the amine group has an affinity for gold and coats the nano-particles, increasing the resistance of the nano-particle film. Creating a water gated P3HT (poly(3-hexylthiophene-2,5-diyl)) OFET without the electro-chemical doping normally experienced by such devices was found to be possible through the use of a calixarene 1 barrier layer, paving the way for the development of an aqueous sensing system.
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Zhang, Qiaoming. "Electrolyte-gated organic field-effect transistors based on organic semiconductor: insulating polymer blends." Doctoral thesis, Universitat Autònoma de Barcelona, 2019. http://hdl.handle.net/10803/667288.
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La presente tesis doctoral se centra en la fabricación, optimización, caracterización y aplicación de capas activas compuestas de una mezcla de semiconductor orgánico y un polímero aislante (OSC:PS) en transistores orgánicos de efecto de campo (EGOFET) con puerta-electrolítica. El EGOFET esta considerado como una prometedora plataforma de detección en el campo de la bioelectrónica debido a su capacidad de operar en medios electrolíticos. Hasta la fecha, aunque en varios proyectos de investigación se ha demostrado su alto potencial como plataforma de detección, existe algunos problemas que deben resolverse, tales como su baja movilidad del portador de carga, lentos tiempo de respuesta y una degradación rápida que dificultan su aplicación práctica. En este contexto, la tesis se divide en tres bloques, que van desde la fabricación de los dispositivos hasta sus aplicaciones.
La primera parte de la tesis tiene como objetivo la fabricación de dispositivo robustos y eficientes empleando dos estrategias: (i) la optimización de la mezclas de polímero aislante y semiconductor orgánico (OSC) y (ii) el uso de una técnica basada en la deposición de capas activas mediante disolución que recibe el nombre de BAMS (bar assistance meniscus shearing). En la primera parte de la tesis (Capitulo 2), se emplearon cuatro semiconductores orgánicos diferentes en que se incluyen tres pequeñas moléculas y un polímero semiconductor como materiales activos. Los dispositivos se han caracterizado mediante medida electricas (características de transferencia y salida) y su analisis y compresión, la sensibilidad potenciométrica, velocidad de conmutación (tiempo de respuesta) y estabilidad eléctrica en agua MilliQ y soluciones salinas (NaCl).
Además, la segunda parte de la tesis (Capítulo 3) está dedicada al desarrollo de un sensor de iones de mercurio basado la exposición de los capas activas a disoluciones acuosa que contienen iones de mercurio. En este caso, se observó un cambio gradual en el potencial umbral, que era respuesta directa de la concentración de iones a la qual se exponia la capa activa. Además, se realizaron pruebas de microscopía de fuerza de atómica “Kelvin-prove” y espectroscopía electroquímica de impedancia con el objetivó de entender el mecanismo de respuesta frente al mercurio. El cual se relaciono con la oxidación/reducción de los iones Hg2+ y la superficie del semiconductor.
Finalmente, la tercera parte de la tesis (Capítulo 4) se centra en la fabricación de nuevos dispositivo sustituyendo el electrolito por un hidrogel (HYGOFET). Logrando dispositivo de alto rendimiento empleando un hidrogel a base de agua como dieléctrico. Además, el HYGOFET muestra una excelente respuesta a los variación de presión debida a la alineación de los dipolos del agua dentro de la capa de semiconductor. Por lo tanto, el dispositivo se puede visualizar como un prototipo de sensor de presión adaptable a ropa inteligente.The present Doctoral Thesis is focused on the fabrication, optimization, characterization and application of organic semiconductors:insulating polymer blends for electrolyte-gated organic field-effect transistors (EGOFETs), which are considered a promising sensing platform in the field of bioelectronics due to their ability to operate in common electrolyte media. Up to date, although several research works have already demonstrated the high potential of using EGOFETs as sensing platform, some unsolved problems (i.e. low carrier mobility, slow response time and fast degradation) are actually hindering their practical application. Within this context, the thesis is divided into three main parts, from EGOFET devices fabrication to their applications. The first part of the thesis aims to obtain robust and efficient EGOFETs device based on two overlooked strategies: (i) the exploitation of blends composed by an insulating polymer and an organic semiconductor (OSC) and (ii) the use of a solution-shearing technique, such as bar-assisted meniscus shearing (BAMS), to deposit the OSC:PS blend. In this part (Chapter 2), four OSCs, including three small molecules and one polymer, were selected as active materials for the fabrication of EGOFETs. The four OSC:polymer blends EGOFET devices have been systematically studied by evaluating and comparing their transfer and output characteristics, potentiometric sensitivity, switching speed and their electrical stability properties recorded in MilliQ water and a NaCl solution as electrolyte media. In addition, the second part of the thesis (Chapter 3) is devoted to the development of a mercury ions sensor based on an EGOFETs by systematically exposing the blend films to a mercury ions aqueous solutions. In this case, a gradual positive threshold voltage shift of the electrical characteristics was observed, which was selected as the detection parameter towards mercury ions. Furthermore, Kelvin probe force microscopy and electrochemical impedance spectroscopy tests were carried out to explore the mechanism of the mercury response, which was demonstrated to be related to the redox reaction between Hg2+ ions and the semiconductor surface. Finally, the third part of the thesis (Chapter 4) is focused on the fabrication of a novel EGOFET device, namely a hydrogel-gated organic field-effect transistor (HYGOFET). A high performance HYGOFET device was achieved by replacing the liquid electrolyte with a water-based hydrogel to serve as dielectric layer. Furthermore, the HYGOFET exhibits an excellent response to pressure stimuli due to the alignment of water dipoles within the OSC layer. The device can thus be envisioned as proof of concept device which can be find applications in the field of textile electronic skin.
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Roberson, Luke Bennett. "Understanding organic thin film properties for microelectronic organic field-effect transistors and solar cells." Diss., Available online, Georgia Institute of Technology, 2005, 2005. http://etd.gatech.edu/theses/available/etd-11072005-111532/.
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Thesis (Ph. D.)--Chemistry and Biochemistry, Georgia Institute of Technology, 2006.Mohan Srinivasarao, Committee Member ; David Collard, Committee Member ; Uwe Bunz, Committee Member ; Art Janata, Committee Member ; Marcus Weck, Committee Member ; Laren Tolbert, Committee Chair.
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Campos, García Antonio. "Influence of organic semiconductors morphology, structure and processability on organic field-effect transistors performance." Doctoral thesis, Universitat Autònoma de Barcelona, 2018. http://hdl.handle.net/10803/666648.
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En esta tesis hemos estudiado como la manera de procesar los semiconductores orgánicos puede afectar a su morfología y estructure cristalina. Semiconductores orgánicos de tipo p y n han sido empleados como capas activas en transistores orgánicos de efecto campo (OFETs). Más concretamente, hemos realizado estudios con diferentes semiconductores orgánicos y hemos fabricado transistores con estos semiconductores procesados por solución, con las técnicas de deposición drop casting and bar-assisted meniscus shearing (BAMS), y por evaporación. El propósito de este trabajo ha sido encontrar la correlación entre la estructura molecular, la organización cristalina de las moléculas y la morfología de la capa delgada con las propiedades eléctricas del semiconductor orgánico. También, buscando la mejora del rendimiento y la estabilidad de los dispositivos, los semiconductores orgánicos en esta tesis se han mezclado íntimamente con polímeros aislantes. Además, se ha estudiado en detalle el rol del polímero aislante en la mezcla comparando OFETs basados en películas delgadas constituidas por sólo el semiconductor orgánico con películas delgadas fabricadas a partir de la mezcla de semiconductor y polímero. Por último, la técnica de deposición por spray ha sido estudiada como técnica para depositar contactos orgánicos basados en el metal orgánico tetratiafulvaleno-tetracianoquinodimetano (TTF-TCNQ) y también para la formación de monocristales de semiconductores orgánicos.In this thesis we have studied how the processing of organic semiconductors can affect their morphology and crystal structure. p-Type and n-type organic semiconductors have been employed as active layers in Organic Field-Effect Transistors (OFETs). More in detail, we have performed studies with different organic semiconductors and fabricated transistors based on them by solution (drop casting and bar-assisted meniscus shearing) and by evaporation. The purpose of the work carried out has been elucidating the correlation of the molecular structure, crystal packing and thin film morphology with the electrical properties of the organic semiconductor. Further, aiming at enhancing the performance and stability of the devices, the organic semiconductors used in this thesis were blended with polymer binders. In addition, the effect of the polymer binder has been studied in detail by comparing OFETs based on thin-films of the pristine semiconductor with OFETs based on thin-films of the semiconductor blended with polymers. Finally, spray printing has been explored as technique for depositing organic contacts based on the organic metal tetrathiafulvalene-tetracyanoquinodimethane (TTF-TCNQ) and also for forming single crystals of organic semiconductors.
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Del, Pozo León Freddy G. "Coating engineering of composite materials for organic field-effect transistors." Doctoral thesis, Universitat Autònoma de Barcelona, 2014. http://hdl.handle.net/10803/284993.
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Esta tesis describe el desarrollo de una tecnología para depositar películas delgadas de polímeros aislantes y materiales compuestos, para aplicaciones en transistores orgánicos de efecto de campo (OFETs). Los materiales compuestos se componen de un semiconductor y un aislante. El aislante es el aglutinante y el semiconductor el material activo. Los materiales activos son polímeros o moléculas pequeñas. Los aglutinantes son estirenos, metacrilatos o combinaciones de ambos. A fin de demostrar las capacidades de la tecnología desarrollada, nombrada Bar Assisted Meniscus Shearing (BAMS), películas delgadas de poliestireno sobre Si/SiOx fueron depositadas, espesores típicos en el intervalo de 50 a 80 nm se encontraron, también valores de RMS en el rango de 0,5 a 0,6 nm fueron determinados, y confirma que películas muy lisas fueron formadas con aplicación tentativa a dieléctricos. Poli (3-hexiltiofeno) (P3HT) es ampliamente utilizado en transistores orgánicos de efecto de campo. Materiales compuestos basados en P3HT y poliestireno fueron probados. OFETs basados en materiales compuestos que sólo utilizan un 10% del material activo (P3HT) mostraron una movilidad de 0,1 cm2V-1s-1 y dicho valor coincide con el valor máximo de mobilidad reportado en literatura hasta la fecha para P3HT puro. Es importante destacar que todos los OFETs fabricados por BAMS usando materiales compuestos tienen voltajes de umbral alrededor de cero voltios a pesar de que toda la fabricación y caracterización se llevo a cabo en aire. Los semiconductores poliméricos juegan un papel muy importante dentro de los semiconductores orgánicos, debido a su ventaja de la capacidad de procesamiento. Por otra parte, las moléculas pequeñas carecen de procesabilidad pero en general poseen una alta mobilidad. Así, materiales compuestos se han desarrollaron para añadir procesabilidad a las pequeñas moléculas, pero tratando de mantener una alta mobilidad. Derivados del TTF, dibenzo - tetratiafulvaleno (DB-TTF), ditiofeno - tetratiafulvaleno (DT-TTF) y bis (etylenetio) - tetratiafulvaleno (BET-TTF) fueron las tres moléculas pequeñas investigadas. En primer lugar, películas térmicamente evaporadas de DB-TTF y BET-TTF puros fueron investigadas y su estabilidad en aire evaluada, se encontró que ambos son extremadamente inestables en presencia de oxígeno y agua. La inclusión de BAMs ha demostrado ser eficaz para producir OFETs basados en materiales compuestos. En primer lugar, se investigaron mezclas de poli (-metil-estireno) (PAMS), y DB-TTF. Los OFETs fabricados muestran estabilidad en aire y características de salida y de transferencia como las de un libro de texto, todas con mobilidades aceptables en el rango de 10-3 cm2V-1s-1. También OFETs a base de poliestireno isotáctico y DB-TTF se investigaron y mobilidades en el intervalo de 10-2 cm2V-1s-1 fueron encontradas. Además, una investigación de composiciones para los materiales compuestos se llevo a cabo, variando relaciones de mezcla y el peso molecular del poliestireno. Dicha investigación reveló que la mejor combinación es la relación de DB-TTF y poliestireno para GPC 3000 (PS3000) en una proporción 1: 2. Después de un estudio a fondo se obtuvo una mobilidad promedio para tal mezcla en el rango de 10-1 cm2V-1s-1 y tensiones umbrales cercanas a cero voltios, sin embargo vale la pena destacar que valores de mobilidad tan altos como 0.7 cm2V-1s-1 fueron encontrados. Medidas en función de la temperatura fueron llevadas a cabo y revelaron que el transporte de carga para estos dispositivos (DB-TTF: PS3000 1: 2) apuntan hacia una movilidad independiente de la temperatura, que correctos a nuestro saber y entender es el primer semiconductor orgánico procesado en solución que exhibe tal comportamiento. Otro comportamiento digno de resaltar fue el encontrado cuando los dispositivos constituyen inversores, ganancias tan altas como 300 fueron encontradas, lo que también a la actualidad es el valor de ganancia más alta para inversores orgánicos.This thesis describes the development of a technology to deposit thin films of insulating polymers and composite materials for applications in organic field-effect transistors (OFETs). Composite materials are comprised of a semiconductor and an insulator. The insulator is the binder and the semiconductor the active material. The active materials are either polymers or small molecules. Binders are styrenes, methacrylates or combinations of both. In order to first demonstrate the capabilities of the technology developed, namely Bar Assisted Meniscus Sheering (BAMs), thin films of polystyrene on Si/SiOx were deposited, typical thicknesses in the range of 50 to 80 nm were found, also RMS values in the range of 0.5 – 0.6 nm were found as well, and confirms very smooth films with tentative application as dielectrics. Poly-(3-hexylthiophene) (P3HT) is widely used is organic field-effect transistors. Composite materials comprised of P3HT and polystyrene were tested. OFETs fabricated based on composites which only use a 10 % of the active material exhibited a mobility of 0.1 cm2V-1s-1 such value match the maximum mobility value reported in literature to-date for pure P3HT. It is important to highlight that all OFETs fabricated by BAMS using based on the composites have threshold voltages around zero volts despite the fact that all fabrication and characterization were carried out in air. Polymeric semiconductors plays a very important role inside organic semiconductors, due to their advantage the processability. On the other hand, small-molecules lacks processability but in general possess high mobility than polymeric semiconductors. So, composite materials were devised to add processability to small-molecules, but trying to maintain high mobility. TTF derivatives, dibenzo - tetharthiafulvalene (DB-TTF), dithiophene - tetrathiafulvalene (DT-TTF) and bis(ethylenethio) – tetrathiafulvalene (BET-TTF) were the three small-molecules investigated. First, thermally evaporated films of pure DB-TTF and BET-TTF were investigated and their stability in air assessed, found that both are extremely unstable under the presence of oxygen and water even at ppm levels. The inclusion of BAMs have been proven effective in order to produce OFETs based on composites -- insulator binder and TTF-derivatives. First, poly−(−μετηψλ styrene) PAMS, and DB-TTF composites were investigated. OFETs fabricated shows stability in air and text-book like output and transfer characteristics, all with acceptable mobilities in the range of 10-3 cm2V-1s-1. Also OFETs based on isotactic polystyrene and DB-TTF were investigated reporting mobilities in the range of 10-2 cm2V-1s-1. Further, an screening of compositions for composites were carried out, varying blend ratios and the molecular weight of the polystyrene. The screening was carried out using bottom and top contact devices. The screening revealed that the best performing blend is DB-TTF and polystyrene for GPC 3000 (PS3000) in a ratio 1:2. After an in-depth study have been conducted found average mobility for such blend in the range of 10-1 cm2V-1s-1 and threshold voltages close to zero volts were also found, however is worth to highlight that mobility values as high as 0.7 cm2V-1s-1 were also found. Temperature measurements have been carried out and revealed that the charge transport found for these devices (DB-TTF:PS3000 1:2) point towards a temperature independent mobility, that to the best of our knowledge to-date is the first organic solution processed semiconductor that exhibits such behavior. Also when devices construct inverters gains as high as 300 were found, which also to-date and to the best of our knowledge is the highest gain value for organic based inverters.
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Hauff, Elizabeth von. "Field effect investigations of charge carrier transport in organic semiconductors." [S.l.] : [s.n.], 2005. http://deposit.ddb.de/cgi-bin/dokserv?idn=981450210.
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Barker, Paul Simon. "Gas sensing using an organic/silicon hybrid field-effect transistor." Thesis, Durham University, 1996. http://etheses.dur.ac.uk/5166/.
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This thesis describes the fabrication and properties of novel organic/silicon hybrid field-effect transistor gas sensors. Whilst most of the work used the emeraldine base form of the conductive polymer polyaniline, the response of a device incorporating a metal-free phthalocyanine is also reported. Arrays of p-type transistors in which the gate electrodes were replaced by 'charge-flow' capacitors were fabricated using standard semiconductor processing techniques. Each array consisted of four devices in which the width of metallisation removed from the gate electrode (total width 72 µm) varied from 0 µm (i.e. the control device) to 35 µm. Thin films of the gas-sensitive organic materials were deposited by spin-coating, and chemically patterned within the holes in the gate metallisation. A delay, referred to as the 'turn-on' response, was observed in the drain current on application of a gate voltage. This was shown to depend on the temperature, level of humidity and the presence of certain gases. The electrical operating characteristics of the hybrid device with and without the polyaniline were examined. These included capacitance-voltage measurements, the 'turn-on' response at different temperatures and the variation of threshold voltage with temperature. From these results an understanding of the effect of integrating polyaniline within a p-channel transistor structure was obtained. The 35 µm gate-hole sensor incorporating polyaniline was found to be sensitive to NO(_x) and SO(_2) at room temperature at concentrations as low as 1 or 2 ppm. Decreasing the gate-hole area, and therefore the surface area of polyaniline, reduced the sensitivity of the device. The reactions were found to be reversible, although complete recovery required approximately eight hours. A similar sensor incorporating a metal-free phthalocyanine compound was reversibly sensitive to 2 ppm NO(_x) with a more rapid recovery of five hours. There was no observable response to SO(_2) or H(_2)S up to 30 ppm.
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Generali, Gianluca <1977>. "Organic heterostructure approach for multifunctional light-emitting field-effect transistors." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2011. http://amsdottorato.unibo.it/3568/.
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The possibility of combining different functionalities in a single device is of great relevance for further development of organic electronics in integrated components and circuitry. Organic light-emitting transistors (OLETs) have been demonstrated to be able to combine in a single device the electrical switching functionality of a field-effect transistor and the capability of light generation.
A novel strategy in OLET realization is the tri-layer vertical hetero-junction. This configuration is similar to the bi-layer except for the presence of a new middle layer between the two transport layers. This “recombination” layer presents high emission quantum efficiency and OLED-like (Organic Light-Emitting Diode) vertical bulk mobility value.
The key idea of the vertical tri-layer hetero-junction approach in realizing OLETs is that each layer has to be optimized according to its specific function (charge transport, energy transfer, radiative exciton recombination). Clearly, matching the overall device characteristics with the functional properties of the single materials composing the active region of the OFET, is a great challenge that requires a deep investigation of the morphological, optical and electrical features of the system.
As in the case of the bi-layer based OLETs, it is clear that the interfaces between the dielectric and the bottom transport layer and between the recombination and the top transport layer are crucial for guaranteeing good ambipolar field-effect electrical characteristics. Moreover interfaces between the bottom transport and the recombination layer and between the recombination and the top transport layer should provide the favourable conditions for the charge percolation to happen in the recombination layer and form excitons.
Organic light emitting transistor based on the tri-layer approach with external quantum efficiency out-performing the OLED state of the art has been recently demonstrated [Capelli et al., Nat. Mater. 9 (2010) 496-503] widening the scientific and technological interest in this field of research.
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Sinno, Hiam. "Polyelectrolyte-Gated Organic Field Effect Transistors – Printing and Electrical Stability." Doctoral thesis, Linköpings universitet, Fysik och elektroteknik, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-98439.
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The progress in materials science during recent decades along with the steadily growing desire to accomplish novel functionalities in electronic devices and the continuous strive to achieve a more efficient manufacturing process such as low‐cost robust high‐volume printing techniques, has brought the organic electronics field to light. For example, organic field effect transistors (OFETs) are the fundamental building blocks of flexible electronics. OFETs present several potential advantages, such as solution processability of organic materials enabling their deposition by various printing methods at low processing temperatures, the possibility to coat large areas, and the mechanical flexibility of polymers that is compatible with plastic substrates. Employing polyelectrolytes as gate insulators in OFETs allows low‐voltage operation in the range of 1 V, suppresses unintended electrochemical doping of the semiconductor bulk, and provides tolerance to thicker gate insulator layers and to the gate electrode alignment over the channel which eases the design and manufacturing requirements. These features place polyelectrolyte‐gated OFETs (EGOFETs) as promising candidates to be realized in lowcost, large‐area, light‐weight, flexible electronic applications. The work in this thesis focuses on EGOFETs and their manufacturing using the inkjet printing technology. EGOFETs have been previously demonstrated using conventional manufacturing techniques. Several challenges have to be overcome when attempting to achieve a fully printed EGOFET, with the incompatible wetting characteristics of the semiconductor/polyelectrolyte interface being one of the main problems. This issue is addressed in paper I and paper II. Paper I presents a surface modification treatment where an amphiphilic diblock copolymer is deposited on the surface to enable the printability of the semiconductor on top of the polyelectrolyte. Paper II introduces an amphiphilic semiconducting copolymer that can switch its surface from hydrophobic to hydrophilic, when spread as thin film, upon exposure to water. Moreover, characterization of the reliability and stability of EGOFETs in terms of bias stress is reported. Bias stress is an undesired operational instability, usually manifested as a decay in the drain current, triggered by the gradual shift of the threshold voltage of the transistor under prolonged operation. This effect has been extensively studied in different OFET structures, but a proper understanding of how it is manifested in EGOFETs is still lacking. Bias stress depends strongly on the material, how it is processed, and on the transistor operating conditions. Papers III and IV report bias stress effects in EGOFET devices and inverters, respectively. The proposed mechanism involves an electron transfer reaction between adsorbed water and the charged semiconductor channel, which promotes the generation of extra protons that subsequently diffuse into the polyelectrolyte. Understanding and controlling the mechanism of bias stress in EGOFETs is crucial for further advancements and development towards commercially viable organic transistor circuits.
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Verma, Vishash. "Improved Slope Estimation in Organic Field-Effect Transistor Mobility Estimation." Kent State University / OhioLINK, 2021. http://rave.ohiolink.edu/etdc/view?acc_num=kent1618703169092189.
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Li, Xiang. "Organic Molecules for Field Effect Transistors and Redox Flow Batteries." University of Akron / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=akron1601396172154889.
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Sahin, Tiras Kevser. "Magnetic field effect and other spectroscopies of organic semiconductor and hybrid organic-inorganic perovskite devices." Diss., University of Iowa, 2018. https://ir.uiowa.edu/etd/6495.
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This thesis consists of three main studies: magnetic field effects in thermally activated delayed fluorescent (TADF) organic light emitting diodes (OLEDs), magnetic field effects in bipolar and unipolar polythiophene (P3HT) devices and a study of hybrid organic/inorganic perovskite devices.
Spin-dependent transport and recombination processes of spin-pair species have been detected by magnetic field effect (MFE) technique in carbon-based semi- conductor devices. Magneto-electroluminescence (MEL) and magneto-conductivity have been measured as a function of the applied magnetic field, B, in light emitting diodes. TADF materials have been used instead of simple fluorescent materials in OLEDs. We have observed very large magnetic response with TADF materials.
The second study is magnetic field effects of regio-regular P3HT based OLED devices. P3HT is a well known semiconducting polymer, and its electrical properties such as magneto-conductance can be affected by an applied magnetic field. P3HT was chosen because it exhibits a sign change in magnetoresistance (MR) as the bias is increased. Unipolar and bipolar devices have been fabricated with different electrode materials to understand which model can be best to explain organic magnetoresistance effect, possibly depending on the operating regime of the device. Transport and luminescence spectroscopies were studied to isolate the different mechanisms and identify their fingerprints.
The third study is on hybrid organic-inorganic perovskite devices. With the potential of achieving very high efficiencies and the very low production costs, perovskite solar cells have become commercially attractive. Scanning electron microscopy (SEM) images and absorption spectrum of the films were compared in single-step solution, two-step solution and solution-assisted vapor deposition techniques. Grain size, morphology and thickness parameters of perovskite films were studied within these techniques. Perovskite solar cells were fabricated and their efficiencies were measured.
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Kalb, Wolfgang L. "Trap states in organic field-effect transistors: quantification, identification and elimination /." Zürich : ETH, 2009. http://e-collection.ethbib.ethz.ch/show?type=diss&nr=18324.
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Temiño, Gutiérrez Inés. "Solution-processed organic field-effect transistors: from fundamental aspects to applications." Doctoral thesis, Universitat Autònoma de Barcelona, 2019. http://hdl.handle.net/10803/669373.
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En esta tesis hemos estudiado varios factores relacionados con los transistores orgánicos de efecto campo (OFETs) procesados por solución, incluyendo su fabricación, su caracterización eléctrica y posibles aplicaciones, especialmente en el campo de sensores físicos. En este trabajo se han utilizado principalmente disoluciones de diferentes semiconductores orgánicos (OSC) de pequeña molécula tipo-p y polímeros aislantes. La deposición de estas mezclas para obtener las capas activas de los OFETs se ha llevado a cabo mediante una técnica de procesado por solución escalable, en concreto la denominada bar-assisted meniscus shearing (BAMS). El propósito principal de este trabajo ha sido comprender la influencia que tienen los parámetros de fabricación elegidos sobre las propiedades morfológicas y estructurales de las capas activas resultantes, y, por tanto, su impacto en las propiedades eléctricas de los dispositivos finales. Se ha realizado un estudio detallado a escala nanométrica de capas basadas en OSC:polímero aislante, descifrando la separación vertical de ambos componentes y el efecto que tiene sobre la estabilidad y el rendimiento de los dispositivos. Además, se han explorado diferentes métodos de dopaje con el objetivo de mejorar las características eléctricas de los OFETs que sufren de una alta resistencia de contacto. También se ha estudiado la relación entre propiedades morfológicas y eléctricas empleando dispositivos flexibles sometidos a tensión mecánica. Finalmente, gracias a la optimización de los parámetros de procesado se han fabricado OFETs con una alta sensibilidad a radiación de rayos-X, explicando a su vez cómo la morfología y el transporte de carga en la capa activa determinan la respuesta de estos dispositivos.In this thesis we have studied several aspects related to organic field-effect transistors (OFETs) printed from solution, including their fabrication, their electrical characterisation, and further applications, especially in the field of physical sensing. Blends of different p‑type small molecule organic semiconductors (OSCs) and insulating polymer binders have been employed in this research work. For the deposition of such blends as active layers for OFETs a scalable solution processing technique has been exploited, namely bar‑assisted meniscus shearing (BAMS). The main purpose of the work carried out has been understanding the influence of the fabrication parameters of choice on the morphological and structural features of the resulting active layer and, thus, their impact on the electrical performance of the final devices. A detailed nanoscale study of OSC:insulating polymer thin films has been conducted, elucidating the vertical stratification of both components and its effect on the devices stability and performance. Further, aiming at improving the electrical characteristics of devices exhibiting high contact resistance values, different doping methodologies have been explored. In addition, the morphology-performance relationship has been studied for flexible OFET devices subjected to mechanical strain. Finally, OFETs exhibiting high sensitivity to X-ray radiation have been fabricated by optimising the processing parameters, rationalising how the morphological and transport properties of the active layer determine the sensing capability of such devices.
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Gay, Nicolas [Verfasser]. "Analog Circuit Design based on Organic Field-Effect Transistors / Nicolas Gay." Aachen : Shaker, 2007. http://d-nb.info/1166509966/34.
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Chang, Wendi. "Characterization of Local field effect in organic film using pressure technique." Thesis, Massachusetts Institute of Technology, 2013. http://hdl.handle.net/1721.1/82374.
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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2013.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 63-65).
This thesis proposes and demonstrates a pressure probing technique for studying the effects of local dielectric changes on the excitonic energy levels in amorphous organic thin films for optoelectronic device applications. Compression of organic films causes a decrease in intermolecular spacing and, through solvation effects, lowers the exciton transition energy. A series of steady-state photoluminescence (PL) measurements performed on doped organic thin films demonstrated the applicability of pressure probing in measuring solvation effects, and fitted to solvation theory. Since a pressure probing technique eliminates composition differences and sample-to-sample variability, in comparison with doping methods, it may be a simpler method of observing energy shifts in solvation effects. Further investigation into spectral diffusion for films under compression indicates a change in spectral diffusion rate due to change in molecular packing density. Comparisons were made between spectral diffusion rates for films under pressure and films of different doping concentrations. Initial measurements of pressure effects on exciplex charge-transfer states in bulk heterojunction films are performed to show change in emission lifetimes. This work could provide a better understanding of the singlet-triplet exciton coupling rates and have a significant impact on device optimization for organic light-emitting diodes (OLEDs) and solar cell applications.
by Wendi Chang.
S.M.
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Wasapinyokul, Kamol. "Effects of illumination on the properties of organic field-effect transistors." Thesis, University of Cambridge, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.609509.
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Jin, Jiyang. "Synthesis of Novel Hydrogen-Bonding Unit for Organic Field-Effect Transistors." University of Akron / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=akron1460047707.
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Braga, Daniele. "Charge transport properties of organic semiconductors : application to field effect transistors." Paris 7, 2009. http://www.theses.fr/2009PA077157.
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Nous avons caractérisé différents configurations de transistors organiques à effet de champ (OFETs) en utilisant des monocristaux de rubrène. Ce dernier est un matériau organique fortement ordonné avec lequel il est possible d'obtenir des mobilité élevée. Tout d'abord, nous avons étudié les propriétés du monocristal de rubrène, en analysant les caractéristiques courant-tension de diodes symétriques avec la théorie du courant limité par la charge d'espace (SCLC). Cette étude nous a permis de montrer que ce matériau se caractérise par une faible densité de défauts ainsi qu'une faible densité de porteurs de charge générés thermiquement. A partir de ce résultat, nous avons analysé transistors organiques à jonction métal/semiconducteur (MESFETs). Ces dispositifs non-conventionnels se sont révélés être des FETs performants, où l'injection des porteurs de charges de la source est contrôlée par la tension appliquée à la grille, choisie de manière à former un contact non-ohmique avec le semiconducteur. Finalement, nous avons étudié les transistors à jonction métal/isolant/semiconducteur (MISFETs). Le comportement courant-tension en-dessous de la tension de seuil ne varie pas de fonction exponentielle, contrairement à la prédiction de la théorie inorganiques. Un comportement linéaire, fonction de la tension de grille est observé excepté sur une région étroite de transition dans laquelle le comportement est pseudo-exponentiel. Une description semi-analytique alternative a été établie en prenant en compte l'effet d'un niveau de pièges localisé sur la distribution de charges libres dans le canal. Niveau dont la présence a été précédemment mise en évidence lors de l'analyse SCLCIn order to go deeper in the knowledge of the fundamentals of Organic Field Effect Transistors (OFETs), we have characterized different typologies of OFETs using rubrene single crystals. The latter are highly ordered organic semiconductors with which high mobility transistors can be fabricated. First we have obtained a detailed picture about the properties of a rubrene single crystal, by analyzing the current-voltage (I-V) characteristics of symmetric diodes with the Space Charge Limited Current (SCLC) theory. A low density of defects and a low density of intrinsic thermally generated carriers have been found to characterize this material. On this basis, we have analyzed metal-semiconductor-field-effect-transistors (MESFETs). These non-conventional devices have been proved to be efficient organic FETs, in which the process of charge carrier injection from the ohmic source contact is controlled by the voltage applied to a non-ohmic gate electrode. Finally, metal-insulator-semiconductor field effect ; transistors (MISFETs) have been considered. The (I-V) trend below the threshold voltage is not exponential, as predicted by the inorganic theory; instead, it is linear with the gate voltage and it follows a pseudo-exponential behaviour only in a narrow transition region. An alternative semi-analytical description has been provided here by taking into account the effect of a localized trap level on the distribution of free charges. The presence of this discrete trap level was highlighted by the previously conducted SCLC analysis
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Chien, Yu-Mo 1980. "Survey of techniques for improving performance of organic transistors." Thesis, McGill University, 2007. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=100224.
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Organic field-effect transistors (OFETs) with region-regular poly(3-hexylthiophene) (rr-P3HT) as active semiconductor were fabricated and characterized. Various methods for improving device performance were investigated. These methods include: the use of dip coating technique (rather than spin coating), thermal annealing, polymer doping with iron chloride (FeCl 3), and stamping of "dry" poly(dimethylsiloxane) (PDMS) stamp before polymer deposition.Through experimental results, it is clear that thermal annealing increases charge carrier mobility of P3HT OFETs. On average an increase of four times in charge mobility was observed after thermal annealing was performed. Dip coated samples also resulted in higher mobility values than spin coated samples. Highest charge mobility value achieved were was ∼0.02 cm2/Vs for dip coated samples, where as the highest value for spin coated devices was around 6e-3 cm2/Vs.
"Dry" stamping of a PDMS devices yielded devices with higher mobility values by around 100% compared to unstamped counterparts. These devices also exhibited lower parasitic leakage currents.
Devices doped with FeCl3 did not perform very well. It is suspected that it was increased so much that it became impossible to turn off the devices.
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Chen, Hang. "Modulation Effects on Organic Electronics." Diss., Georgia Institute of Technology, 2005. http://hdl.handle.net/1853/7594.
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A high aspect ratio epoxy mask has been built with Taiyo PSR4000BN on chemical sensing array chip. Thickness up to 200 and #61549;m and aspect ratio up to 16:1 have been achieved with this material. It is demonstrated that this material satisfies the mechanical and chemical requirements. A three-electrode system has been designed and built for electrochemistry in micro-cell on chip. Tests with poly(phenylenesulfide-phenyleneamine) (PPSA) demonstrates that it is possible to precisely tune the properties (Work function and resistance) of conducting polymer that has been cast on chip surface.
A new test platform GT03 has been fabricated and used to characterize the chemical effects on organic electronics. It is demonstrated that the chemical species in ambient environment can affect organic electronics properties on bulk, interface and electric contact. The contact resistance in organic field-effect transistors (OFETs) has been characterized with modified interdigitated structure (IDS). It is demonstrated that drain and source contact resistances can be calculated separately with modified four-point-probe measurements, and contact resistance and material bulk resistance are actually modulated by the gate electric field. Furthermore, the influence from oxygen doping in poly(3-hexylthiophene) (P3HT) based OFETs has been investigated. A new model of oxygen doping has been suggested and it is demonstrated that oxygen doping can affect all the resistance components in P3HT OFETs.
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Granger, Devin B. "ACENES, HETEROACENES AND ANALOGOUS MOLECULES FOR ORGANIC PHOTOVOLTAIC AND FIELD EFFECT TRANSISTOR APPLICATIONS." UKnowledge, 2017. http://uknowledge.uky.edu/chemistry_etds/76.
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Polycyclic aromatic hydrocarbons composed of benzenoid rings fused in a linear fashion comprise the class of compounds known as acenes. The structures containing three to six ring fusions are brightly colored and possess band gaps and charge transport efficiencies sufficient for semiconductor applications. These molecules have been investigated throughout the past several decades to assess their optoelectronic properties. The absorption, emission and charge transport properties of this series of molecules has been studied extensively to elucidate structure-property relationships. A wide variety of analogous molecules, incorporating heterocycles in place of benzenoid rings, demonstrate similar properties to the parent compounds and have likewise been investigated.
Functionalization of acene compounds by placement of groups around the molecule affects the way in which molecules interact in the solid state, in addition to the energetics of the molecule. The use of electron donating or electron withdrawing groups affects the frontier molecular orbitals and thus affects the optical and electronic gaps of the molecules. The use of bulky side groups such as alkylsilylethynyl groups allows for crystal engineering of molecular aggregates, and changing the volume and dimensions of the alkylsilyl groups affects the intermolecular interactions and thus changes the packing motif.
In chapter 2, a series of tetracene and pentacene molecules with strongly electron withdrawing groups is described. The investigation focuses on the change in energetics of the frontier molecular orbitals between the base acene and the nitrile and dicyanovinyl derivatives as well as the differences between the pentacene and tetracene molecules. The differences in close packing motifs through use of bulky alkylsilylethynyl groups is also discussed in relation to electron acceptor material design and bulk heterojunction organic photovoltaic characteristics.
Chapter 3 focuses on molecular acceptor and donor molecules for bulk heterojunction organic photovoltaics based on anthrathiophene and benzo[1,2-b:4,5-b’]dithiophene central units like literature molecules containing fluorene and dithieno[2,3-b:2’,3’-d]silole cores. The synthetic strategies of developing reduced symmetry benzo[1,2-b:4,5-b’]dithiophene to study the effect of substitution around the central unit is also described. The optical and electronic properties of the donors and acceptors are described along with the performance and characteristics of devices employing these molecules.
The final two data chapters focus on new nitrogen containing polycyclic hydrocarbons containing indolizine and (2.2.2) cyclazine units. The optical, electronic and other physical properties of these molecules are explored, in addition to the synthetic strategies for incorporating the indolizine and cyclazine units. By use of alkylsilylethynyl groups, crystal engineering was investigated for the benzo[2,3-b:5,6-b’]diindolizine chromophore described in chapter 4 to target the 2-D “brick-work” packing motif for application in field effect transistor devices. Optical and electronic properties of the cyclazine end-capped acene molecules described in chapter 5 were investigated and described in relation to the base acene molecules. In both cases, density functional theory calculations were conducted to better understand unexpected optical properties of these molecules, which are like the linear acene series despite the non-linear attachment.
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Castro, Carranza Alejandra. "Umem-based capacitance model for organic field effect transistors: development and implementation." Doctoral thesis, Universitat Rovira i Virgili, 2013. http://hdl.handle.net/10803/111164.
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En este trabajo de tesis se ha desarrollado un nuevo modelo analítico y compacto de carga y capacitancia para transistores orgánicos de efecto de campo (OFETs por sus siglas en inglés) al que hemos llamado UBCM. El modelo es válido y continuo en todas las regiones de operación del dispositivo, que son acumulación, agotamiento parcial y agotamiento total, asumiendo una operación cuasi-estática, por lo que es válido para bajas y medias frecuencias. Los parámetros aplicados en UBCM son analíticamente extraídos de las características de corriente-voltaje de los OFETs mediante UMEM (Método de Extracción de Parámetros y Modelo Unificado), por lo que UBCM es consistente con el modelo de corriente que describe al dispositivo. Finalmente UBCM se ha implementado en simuladores de circuitos mediante su código en Verilog-A y Spice, y ha sido utilizado en la simulación de inversores orgánicos, resultados que se han validado con mediciones experimentales.We developed a new charge and capacitance analytical compact model for organic field effect transistors (OFETs) which we have called UBCM. The model is continuous and valid in all device operation regimes, i.e. accumulation, partial depletion and total depletion. It operates at low and medium frequencies since a quasi-static operation is assumed. The parameters applied in UBCM are analytically extracted from the current-voltage (I-V) characteristics of the OFETs using the unified model and extraction method (UMEM), thus the capacitance model is consistent with the I-V one. The overlap capacitance effect is taken into account and the frequency dependence is considered empirically by means of the insulator permittivity. Comparisons between modeled and experimental gate-to-channel capacitances of OTFTs based on different materials show the validity of the model. Finally, UBCM was implemented in circuit simulators by means of its Verilog-A and Spice codes to simulate organic inverters.
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Pérez, Rodríguez Ana. "Nanoscale interpretation of performances in organic solar cells and field effect transistors." Doctoral thesis, Universitat Autònoma de Barcelona, 2018. http://hdl.handle.net/10803/565824.
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Dos de los principales retos a superar en el campo de la electrónica orgánica son el control la morfología de la capa semiconductora y las propiedades de las interfases. En particular, las interfases formadas por la capa orgánica semiconductora y los electrodos metálicos influyen fuertemente en el comportamiento de los dispositivos. Hasta el momento se ha dedicado un gran esfuerzo a la mejora de estas interfases siguiendo para ello diferentes estrategias como son el uso de monocapas autoensambladas (SAMs), capas de óxidos metálicos o mediante el dopaje de los contactos. Con respecto a la morfología, se ha probado que ésta juega un papel fundamental en la disociación de los excitones, en la extracción de la carga y en la recombinación en células solares orgánicas (OSCs), así como en las propiedades de trasporte en transistores orgánicos de efecto campo (OFETs). En este trabajo se utiliza principalmente el microscopio de fuerza atómica (AFM) y, en menor medida, otras técnicas de caracterización de superficies, y en la investigación de interfases que forman parte de estos dispositivos. En particular, se ha empleado el microscopio de fricción atómica (FFM), el microscopio de conducción de fuerza atómica (AFM) y el microscopio de Kelvin de fuerza atómica (KPFM) en dispositivos OSC y OFETs, con el objetivo de correlacionar la caracterización a escala nanométrica con el rendimiento macroscópico de los dispositivos. Este documento está organizado de la siguiente forma. Las motivaciones del trabajo se presentan en el Capítulo 1. En el Capítulo 2 se incluye una introducción teórica a los semiconductores orgánicos y a los conceptos de autoensamblado y nanoestructuración. Las técnicas y metodologías empleadas en la tesis se describen en el Capítulo 3. Los resultados se presentan en los capítulos 4, 5, 6 y 7.
En el Capítulo 4 se detalla el fundamento físico del Transverse Shear Microscopy (TSM). La combinación de datos experimentales con resultados de simulaciones numéricas nos ha permitido probar que la señal de TSM tiene naturaleza disipativa.
El Capítulo 5 se centra en el efecto de las capas transportadoras de huecos (HTLs) y su impacto en el rendimiento de células solares fabricados con materiales orgánicos y con perovskitas. Respecto a las células solares, hemos demostrado que el uso de SAMs de ácidos fosfónicos cambia favorablemente la función de trabajo del cátodo de ITO, pero también induce una acumulación de carga en la interfase con efectos negativos en el rendimiento del dispositivo. En las células solares de perovskitas, a pesar de utilizar un material recientemente sintetizado como HTL con una posición del HOMO más favorable, el alineamiento energético en la interfase con el TiO2 resulta menos favorable, dando lugar a peores propiedades de las células solares.
El Capítulo 6 está dedicado al efecto del solvent vapor annealing (SVA) en la cristalinidad y la separación vertical de fase en células solares de oligotiofenos comprobando que, al aplicar el método SVA, los dominios del oligómero muestran mejor cristalinidad, mientras que los dominios del fullereno aumentan en tamaño, mejorando las propiedades fotovoltaicas de los dispositivos.
En el Capítulo 7 hemos realizado una caracterización a escala nanométrica de OFETs fabricados con C8-BTBT:PS mediante FFM de OFETs fabricados con C8-BTBT:PS, que ha permitido resolver la separación vertical de fase del PS y el C8-BTBT. Mediante KPFM, se obtuvieron mapas del potencial de superficie de los OFETs, a partir de los que se han obtenido valores de la resistencia de contacto y de la movilidad de carga para diferentes electrodos y concluyendo que la resistencia de contacto es un factor crítico que limita el rendimiento de estos dispositivos.
Las principales conclusiones de la tesis se incluyen en el Capítulo 8Two of the main challenges in organic electronic devices are the semiconducting layer morphology and the interface properties. Particularly, the interfaces formed by the semiconducting organic layer and the metallic electrodes strongly influence the performance of the devices. Thus, a strong effort has been devoted to improve these interfaces by different approaches such as self assembled monolayers (SAMs), layer of metalic oxides or contact doping. Concerning the morphology, it has been proven that it plays a fundamental role in exciton dissociation, charge collection and recombination in organic solar cells (OSC), as well as in the transport properties in organic field effect transistors (OFETs). In this work we make use of atomic force microscopy (AFM) and, in a lesser extent, of other surface characterization techniques for the study of surfaces and interfaces that conform organic electronic devices. In particular, we focus on the use of friction force microscopy (FFM), conductive atomic force microscopy (C-AFM) and Kelvin probe force microscopy (KPFM) operating modes on OSC and OFETs devices with the goal of correlating the nanoscale characterization with the macroscopic performance of the devices. This thesis is organized in the following way: the motivations of this work are presented in Chapter 1. In Chapter 2 a brief theoretical introduction on organic semiconductors and the concept of self assembly and nanostructuration is given, while in Chapter 3 the techniques employed during this thesis as well as the used methodologies are described. The results are presented in the Chapters 4, 5, 6 and 7. In Chapter 4 we study in detail the physical origin behind Transverse Shear Microscopy (TSM). By combining experimental data with simulations, we prove that the TSM signal has a dissipative origin and we use the technique to obtain the crystalline orientation of tip-induced grown PTCDI-C8 islands. In Chapter 5 we focus on the effect of hole transport layers (HTLs) for both organic and perovskites solar cells. For bulk-heterojunction solar cells (BHJ) we prove that the use of phosphonic acid self assembled monolayers (SAMs) changes the workfunction of the ITO cathode in a favourable way, but also induces a charge accumulation density at the interface with detrimental effects for the cell performance. In perovskite solar cells, despite using newly synthesized HTL with more favourable HOMO position, the energy level alignment at the interface with the TiO2 results less favourable leading to worse photovoltaic device properties. Chapter 6 is devoted to the solvent vapor annealing (SVA) effect on the crystallinity and vertical phase separation on oligothiophene bulkheterojunction solar cells. We prove that, upon SVA, the oligomer domains present better crystallinity while the fullerene domains increase in size, enhancing the photovoltaic performance of the devices. In Chapter 7, a nanoscale characterization by means of FFM was correlated with the device performance for C8-BTBT:PS OFETs, providing with a picture at the nanoscale of the organic films vertical phase separation. By means of KPFM, maps of the surface potential of the OFETs were obtained, allowing us to extract contact resistance and charge mobility values for different electrodes, concluding that the contact resistance is the critical factor limiting the devices performance. Finally, in Chapter 8, the main conclusions of this thesis will be collected.
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Irugulapati, Harista. "Fused Arenes-Based Molecular and Polymeric Materials for Organic Field Effect Transistors." TopSCHOLAR®, 2013. http://digitalcommons.wku.edu/theses/1255.
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In the past decade, tremendous progress has been made in organic field effecttransistors. Fused oligothiophenes and anthracene molecules are fascinatingmacromolecules having unique optoelectronic properties. These compounds are successfully employed as active components in optoelectronic devices including field effect transistors. Our goal is to design and synthesize conjugated molecular materials, which are highly functionalized through structural modifications in order to enhance their electronic, photonic, and morphological properties. The main desire is to synthesize novel organic fused-arenes having efficient charge carrier mobilities, as well as to optimize optical properties for organic field effect transistors (OFETs). Novel series of fused arene molecules of 9,10-di(thiophen-3-yl)anthracene (1), trans-2,5-(dianthracene-9- vinyl)thiophene (2), trans-5,5’-(dianthracene-9-yl)vinyl)- 2,2’-bithiophene (3), 5,5’-di(2 thiophene)-2,2’-bithiophene (4) , 9,10-(divinyl)anthracene core with 1- phenylcarboxypyrene (6) and polymers of poly(anthracene-co-bithiophene) (5) and poly(anthracene) (7) have been synthesized as promising materials for organic field effect transistors (OFETs). These compounds were confirmed and characterized by 1H-NMR, FT-IR, and elemental analysis. Their optical, thermal, and electronic properties were investigated using UV-Vis and photoluminescence spectroscopy, and thermogravimetric analysis respectively. Future studies will focus on evaluating OFETs performance of these material.
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Paulus, Fabian [Verfasser], and Uwe H. F. [Akademischer Betreuer] Bunz. "N-Heteroacenes in Organic Field-Effect Transistors / Fabian Paulus ; Betreuer: Uwe Bunz." Heidelberg : Universitätsbibliothek Heidelberg, 2016. http://d-nb.info/1180615247/34.
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Kyndiah, Adrica <1987>. "Interfacial interactions, charge transport and growth phenomena in Organic Field Effect Transistors." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2015. http://amsdottorato.unibo.it/7100/.
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Organic electronics is an emerging field with a vast number of applications having high potential for commercial success. Although an enormous progress has been made in this research area, many organic electronic applications such as organic opto-electronic devices, organic field effect transistors and organic bioelectronic devices still require further optimization to fulfill the requirements for successful commercialization. The main bottle neck that hinders large scale production of these devices is their performances and stability. The performance of the organic devices largely depends on the charge transport processes occurring at the interfaces of various material that it is composed of. As a result, the key ingredient needed for a successful improvement in the performance and stability of organic electronic devices is an in-depth knowledge of the interfacial interactions and the charge transport phenomena taking place at different interfaces. The aim of this thesis is to address the role of the various interfaces between different material in determining the charge transport properties of organic devices. In this framework, I chose an Organic Field Effect Transistor (OFET) as a model system to carry out this study as it An OFET offers various interfaces that can be investigated as it is made up of stacked layers of various material. In order to probe the intrinsic properties that governs the charge transport, we have to be able to carry out thorough investigation of the interactions taking place down at the accumulation layer thickness. However, since organic materials are highly instable in ambient conditions, it becomes quite impossible to investigate the intrinsic properties of the material without the influence of extrinsic factors like air, moisture and light. For this reason, I have employed a technique called the in situ real-time electrical characterization technique which enables electrical characterization of the OFET during the growth of the semiconductor.
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Lee, Yongjeong. "Gaussian density of states driven numerical modeling of organic field-effect transistors." Thesis, Institut polytechnique de Paris, 2020. http://www.theses.fr/2020IPPAX043.
Full textAbstract:
Bien que la physique des transistors organiques ait été largement étudiée, l'analyse avec la densité d'états Gaussianne fait toujours défaut malgré la nature désordonnée des semi-conducteurs organiques. Étant donné que le transport et l'injection de charges ont lieu à la densité d'états Gaussienne, cette structure énergétique distinctive des semi-conducteurs organiques pourrait rendre le processus d'accumulation de charges, et donc le fonctionnement du dispositif, différent. Cette thèse est consacrée à la compréhension de l'effet de la densité d'états Gaussienne sur les paramètres des transistors organiques, la tension de seuil, la mobilité du porteur de charge et la barrière d'injection via des simulations 2D basées sur des éléments finis numériques et la validation expérimentale. La tension de seuil est comprise par le piégeage de charge dans la secondaire densité d'états Gaussianne ainsi que dans la densité d'états intrinsèque. Nous montrons que le chevauchement des deux densité d'états en raison du désordre induit des comportements de seuil spécifiques des transistors organiques. Deuxièmement, le transport est étudié via le modèle gaussien désordonné sur des sites spatiaux aléatoires de semi-conducteurs organiques. Ce modèle peut offrir un résultat précis par rapport au modèle avec un réseau cubique. De plus, nous proposons une paramétrisation correcte du modèle pour des polymères aux petites molécules. Enfin, la barrière d'injection basée sur la charge et le transport est étudiée et comparée. Les avantages et les limites de chaque modèle sont évaluésAlthough the device physics of organic field-effect transistors (OFETs) has been widely studied, the analysis with energetic distribution of the density-of-states (DOS) is still lacking in spite of the disordered nature of organic semiconductors. Because charge transport and injection take place at the Gaussian DOS, this distinctive energetic structure of organic semiconductors could make the charge-accumulation process, and hence the device operation, different. This thesis is dedicated to understanding the effect of Gaussian DOS on device parameters of OFETs, the threshold voltage, charge-carrier mobility and injection barrier via numerical finite-element based 2D simulations and experimental validation. The threshold voltage is comprehended by the charge trapping into the secondary Gaussian trap DOS as well as the intrinsic Gaussian DOS. We show that the overlap of two Gaussian DOSs due to the disorder induces specific threshold behaviors of OFETs. Second, the hopping transport is studied via Gaussian disordered model (GDM) on random spatial sites of organic semiconductors. This model can offer a precise result over GDM with cubic lattice. Also, we propose a correct parametrization of the model for wide range of materials from polymers to small molecules. Lastly, charge-based and transport-based injection barrier are studied and compared with Gaussian DOS. The advantages and limits of each model are evaluated