We have developed a novel method of producing ultra-short channel graphene field effect devices on SiO2 substrates and have studied their electrical transport properties. A nonlinear current behavior is observed coupled with a quasi-saturation effect. An analytical model is developed to explain this behavior using ballistic transport, where the charge carriers experience minimal scattering. We also observe multilevel resistive switching after the device is electrically stressed. In addition, we have studied the evolution of the electrical transport properties of few-layer graphene during electrical breakdown. We are able to significantly increase the time scale of break junction formation, and we are able to observe changes occurring close to breakdown regime. A decrease in conductivity along with p−type doping of the graphene channel is observed as the device is broken. The addition of structural defects generated by thermal stress caused by high current densities is attributed to the observed evolution of electrical properties during the process of breakdown. We have also studied the effects of the local environment on graphene devices. We encapsulate graphene with poly(methyl methacrylate) (PMMA) polymer and study the electrical transport through in situ measurements. We have observed an overall decrease in doping level after low-temperature annealing in dry-nitrogen, indicating that the solvent in the polymer plays an important role in doping. For few-layer encapsulated graphene devices, we observe stable n−doping. Applying the solvent onto encapsulated devices demonstrates enhanced hysteretic switching between p and n−doped states.

This thesis presents the design of a mixed-signal CMOS multiplier implemented with short-channel PMOS transistors. The multiplier presented here forms the product of a differential input voltage and a five-bit digital code. A TSMC 0.18 µm MOSFET model is used to simulate the circuit in Cadence Design Systems. The research presented in this thesis reveals a configuration that allows the multiplier to run at a speed of 8.2 GHz with end-point nonlinearity less than 5%. The high speed and low nonlinearity make this circuit ideal for applications such as filtering and digital to analog conversion.

The prospect of producing nanometer channel-length thin film transistors (TFTs) for active matrix addressed pixelated arrays opens up new high-performance applications in which the most amenable device topology is the vertical thin film transistor (VTFT) in view of its small area. The previous attempts at fabricating VTFTs have yielded devices with a high drain leakage current, a low ON/OFF current ratio, and no saturation behaviour in the output current at high drain voltages, all induced by short channel effects. To overcome these adversities, particularly dominant as the channel length approaches the nano-scale regime, the reduction of the gate dielectric thickness is essential. However, the problems with scaling the gate dielectric thickness are the high gate leakage current and early dielectric breakdown of the insulator, deteriorating the device performance and reliability. A novel ultra-thin SiNx film suitable for the application as the gate dielectric of short channel TFTs and VTFTs is developed. The deposition is performed in a standard 13.56MHz PECVD system with silane and ammonia precursor gasses diluted in nitrogen. The deposited 50nm SiNx films demonstrate excellent electrical characteristics in terms of a leakage current of 0.1 nA/cm?? and a breakdown electric field of 5.6MV/cm. Subsequently, the state of the art performances of 0.5??m channel length VTFTs with 50 and 30nm thick SiNx gate dielectrics are presented in this thesis. The transistors exhibit ON/OFF current ratios over 10^9, the subthreshold slopes as sharp as 0.23 V/dec, and leakage currents in the fA range. More significantly, a high associated yield is obtained for the fabrication of these devices on 3-inch rigid substrates. Finally, to illustrate the tremendous potential of the VTFT for the large area electronics, a 2.2-inch QVGA AMOLD display with in-pixel VTFT-based driver circuits is designed and fabricated. An outstanding value of 56% compared to the 30% produced by conventional technology is achieved as the aperture ratio of the display. Moreover, the initial measurement results reveal an excellent uniformity of the circuit elements.

Submitted by Liliane Úbeda Morandi Rotoli null (lilianemorandi@yahoo.com.br) on 2016-07-25T12:32:17Z No. of bitstreams: 1 LilianeUbedaMorandiRotoli_PGAD_TUPA_Abril2016.pdf: 4209302 bytes, checksum: cce94f81cce55574df2e78b200a15c4c (MD5) / Approved for entry into archive by Felipe Augusto Arakaki (arakaki@reitoria.unesp.br) on 2016-07-28T11:57:46Z (GMT) No. of bitstreams: 1 rotoli_lum_me_tupa.pdf: 4209302 bytes, checksum: cce94f81cce55574df2e78b200a15c4c (MD5) / Made available in DSpace on 2016-07-28T11:57:46Z (GMT). No. of bitstreams: 1 rotoli_lum_me_tupa.pdf: 4209302 bytes, checksum: cce94f81cce55574df2e78b200a15c4c (MD5) Previous issue date: 2016-04-04 / A agricultura familiar depara-se com diversas barreiras no sistema agropecuário brasileiro. Pode-se citar a falta de estrutura de escoamento da produção, carência de recursos, distância do mercado consumidor e a distribuição do produto no que se refere ao acesso ao mercado e custos das transações. Uma estratégia de diferenciação para os agricultores familiares e que contribui para a competitividade é a produção de produtos orgânicos. Em razão da fragilidade dos agricultores familiares na distribuição dos produtos o agricultor deve eliminar intermediários, e sendo assim, o canal direto de comercialização se torna um mecanismo eficiente para o agricultor. O objeto de análise do presente estudo utilizou o canal direto Community Supported Agriculture (CSA), que é um mecanismo de comercialização de produtos da agricultura, que tem como proposta sustentar a agricultura, especificamente relacionada ao manejo orgânico, por meio de uma proximidade maior entre ambos agentes, agricultor e consumidor, sendo que este último se compromete a realizar pagamentos antecipados para que o agricultor possa produzir seus produtos e planejar a sua produção. Esta pesquisa foi motivada pela análise da relação de comercialização entre os agricultores e consumidores, e utilizou a teoria da Economia dos Custos de Transação (ECT) para dar embasamento teórico à pesquisa. Portanto, o objetivo principal deste estudo foi analisar a estrutura de governança utilizada nas CSAs do Estado de São Paulo e o alinhamento das características das transações e das características dos agentes agricultores e consumidores envolvidos. A pesquisa teve natureza quali - quantitativa, com aplicação do método survey. Os dados foram coletados entre dezembro de 2015 e janeiro de 2016 com 241 famílias (27,5% da população) e 11 agricultores (91,6% da população) do Estado de São Paulo. Os resultados indicaram que a motivação dos agricultores em participar das CSAs envolvem fatores ambientais, proximidade com o consumidor e ideologias, já para os consumidores, o que os motiva são fatores relacionados ao meio ambiente, produtos de qualidade e procedência, e ajudar um agricultor. A análise do ambiente institucional mostrou que a legislação de produção orgânica brasileira é a única regra formal sobre a atividade. Os agricultores e consumidores das CSAs analisadas apresentaram bom alinhamento quanto às características das transações e dos agentes, de modo geral. Os agricultores e consumidores apresentaram desalinhamento quanto à incerteza, mostrando que há necessidade de adaptações no acordo (formal/informal) entre os agentes. Existe racionalidade limitada entre os agentes, uma vez que não há troca de informação em relação a alguns aspectos da transação como por exemplo qualidade e quantidade dos produtos consumidos, previsão de volume produzido, e isto prejudica a previsão de transações futuras. Por fim, a estrutura de governança identificada na relação de comercialização entre agricultores e consumidores é a híbrida e é adequada para a eficiência da coordenação e diminuição dos custos de transação. No entanto, sugere-se que sejam incorporados alguns elementos no acordo para reduzir o nível de incerteza do agricultor, e ainda que tal acordo seja formalizado entre ambas as partes. / Family farming faces several barriers in the Brazilian Agricultural System. Such barriers include the lack of flow of production structure, lack of resources away from the consumer market, distance from the consumer market and the distribution of the product in relation to market access and transaction costs. A differentiation strategy for family farmers that contributes to competitiveness, is the production of organic products. Due to the fragility of family farmers in the distribution of farm products, the elimination of the middleman results in a direct marketing channel, which creates an efficient mechanism for the farmer. The analysis of a current study used the direct channel Community Supported Agriculture (CSA), which is a marketing mechanism for agriculture products used directly between farmer and consumer. The CSA have also proposed a form of sustainable agriculture, specifically related to organic farm management. By having the agents, farmers and consumers, work more closely together, prepayments may be made to the farmer in order to produce products and plan production. This research was conducted in order to analyze the marketing relationship between farmers and consumers, and used the theory of Tansaction-Costs Economics (ECT) to give theoretical basis for research. Therefore, the main objective of this study was to analyze the governance’s structure used in the CSAs of the São Paulo State and the alignment of the transaction characteristics and the characteristics of farmers’ agents and consumers involved. The research was qualitative and quantitative in nature and was applied using the Survey Method. The data was collected between December of 2015 and January of 2016 with 241 families (27.5% of the population) and 11 farmers (91.6% of the population) of São Paulo. The results indicated that the motivation of farmers to participate in CSAs involve environmental factors, as well as proximity to the consumer and ideologies. In contrast, consumers were motivated by factors that related to the environment, product quality and origin, and in the interest of helping the farmer. The analysis of the institutional environment showed that Brazilian organic production legislation is the only formal rule relevant to the activity. The farmers and consumers of CSAs that were analyzed showed good alignment on the characteristics of the transactions between agents. Farmers and consumers showed misalignment as the uncertainty, showing that there is need for adjustments to the agreement (formal / informal) between agents. There is a limited rationality between agents, since there is no exchange of information in relation to some aspects of the transaction such as: quality and quantity of consumed products, prediction of production volumes, and this impairs the prediction of future transactions. Overall, the governance structure identified in the marketing relationship between farmers and consumers is the hybrid and is appropriate for coordination efficiency and decreased transaction costs. However, certain elements, such as the formalization of the arrangements between both parties, should be incorporated within the deal in order to reduce the farmer's level of uncertainty.

Orientador: Andrea Rossi Scalco / Coorientador: Giuliana Santini Pigatto / Coorientador: Nelson Russo de Moraes / Banca: Ana Elisa Smith Bressan Lourenzani / Banca: Kássia Watanabe / Resumo: A agricultura familiar depara-se com diversas barreiras no sistema agropecuário brasileiro. Pode-se citar a falta de estrutura de escoamento da produção, carência de recursos, distância do mercado consumidor e a distribuição do produto no que se refere ao acesso ao mercado e custos das transações. Uma estratégia de diferenciação para os agricultores familiares e que contribui para a competitividade é a produção de produtos orgânicos. Em razão da fragilidade dos agricultores familiares na distribuição dos produtos o agricultor deve eliminar intermediários, e sendo assim, o canal direto de comercialização se torna um mecanismo eficiente para o agricultor. O objeto de análise do presente estudo utilizou o canal direto Community Supported Agriculture (CSA), que é um mecanismo de comercialização de produtos da agricultura, que tem como proposta sustentar a agricultura, especificamente relacionada ao manejo orgânico, por meio de uma proximidade maior entre ambos agentes, agricultor e consumidor, sendo que este último se compromete a realizar pagamentos antecipados para que o agricultor possa produzir seus produtos e planejar a sua produção. Esta pesquisa foi motivada pela análise da relação de comercialização entre os agricultores e consumidores, e utilizou a teoria da Economia dos Custos de Transação (ECT) para dar embasamento teórico à pesquisa. Portanto, o objetivo principal deste estudo foi analisar a estrutura de governança utilizada nas CSAs do Estado de São Paulo e o alinham... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: Family farming faces several barriers in the Brazilian Agricultural System. Such barriers include the lack of flow of production structure, lack of resources away from the consumer market, distance from the consumer market and the distribution of the product in relation to market access and transaction costs. A differentiation strategy for family farmers that contributes to competitiveness, is the production of organic products. Due to the fragility of family farmers in the distribution of farm products, the elimination of the middleman results in a direct marketing channel, which creates an efficient mechanism for the farmer. The analysis of a current study used the direct channel Community Supported Agriculture (CSA), which is a marketing mechanism for agriculture products used directly between farmer and consumer. The CSA have also proposed a form of sustainable agriculture, specifically related to organic farm management. By having the agents, farmers and consumers, work more closely together, prepayments may be made to the farmer in order to produce products and plan production. This research was conducted in order to analyze the marketing relationship between farmers and consumers, and used the theory of Tansaction-Costs Economics (ECT) to give theoretical basis for research. Therefore, the main objective of this study was to analyze the governance's structure used in the CSAs of the São Paulo State and the alignment of the transaction characteristics and the character... (Complete abstract click electronic access below) / Mestre

Scaling has been pivotal in the success of the Moore's law. Using scaling techniques to improve the MOSFET comes at a risk of growing short channel effects. This publication deals with the theoretical study of impact of gate length scaling on planar bulk MOSFET. A systematical study shows that the impact of short channel effects like drain induced barrier lowering, subthreshold leakage, hot carrier generation and channel length modulation grows with gate length scaling. Thereby degrading the MOSFET performance. In addition to the numerical device simulation an analytical modelling of the device is also performed. Though the analytical model explains the device characteristic trends, it is found to be quantitative inaccurate in comparison to the numerical model especially when scaling below deep sub-micrometer regime.

Organic field-effect transistors (OFETs) are essential devices for the realization of novel electronic applications based on organic materials. Recent years have brought tremendous improvements regarding the organic semiconductor (OSC) with charge carrier mobilities around 10 cm²/Vs. Yet, several challenges are needed to be addressed in order to enable technologies of the future that are based on high-performance organic transistors. In this work, C8-BTBT, a high-mobility material that has gained increasing interest in the last few years, is used to prepare films with state-of-the art charge-carrier mobility and above. For this purpose, the solution-shearing method—a meniscus-guided technique that is capable to produce highly aligned, crystalline films—is applied. Based on these charge-transport layers with an estimated intrinsic mobility of up to 12 cm²/Vs, several strategies towards their exploitation for high-performance organic transistors are investigated. Among the relevant parameter, channel length, contact resistance and gate dielectric capacitance are the three aspects that are addressed. The solution-shearing method is further applied to the realization of solution-deposited polymer dielectrics. High-capacitance films with maximum values of about 280 nF/cm² are fabricated and used to produce low-voltage OFETs that can operate at -1V. In order to increase the devices’ transconductance, a novel patterning methodology to achieve sub-micrometre channel lengths is investigated. Using this technique, working devices with a channel length of 500 nm are shown. The compatibility of this process with the solution-shearing method for the fabrication of high-performance semiconducting and gate dielectric films is one of its major advantages. One of the limiting device parameters is the contact resistance as is clearly observable by the restricted current scaling that is observed for lower channel length. Hence, the interface of OSC and source/drain contacts is investigated. Even though an ultimate solution for very low contact resistance remains to be developed, important aspects for its further enhancement are deduced in this work. As an important first experimental result, this thesis describes a short-channel device architecture that is compatible with solution-shearing of high-performance films with its full potential yet to be explored in future work. / Organische Feld-Effekt Transistoren (OFETs) sind grundlegende Bestandteile für die Entwicklung neuerartiger Technologien auf der Basis von organischen Halbleitermaterialien. Insbesondere während der letzten Jahre haben diese Materialien einschlägige Verbesserungen erfahren und erreichen heute Ladungsträgermobilitäten um die 10 cm²/Vs. Um dies für die Umsetzung neuartiger Technologien zu nutzen, müssen jedoch noch einige Herausforderungen überwunden werden. Diese Arbeit leistet einen Beitrag in diese Richtung. Unter Anwendung eines der wohl populärsten Halbleitermaterialien der letzen Jahre mit der chemischen Bezeichnung C8-BTBT, wird die Herstellung von hochqualitativen Halbleiterfilmen mittels Flüssigprozessierung gezeigt. Mit der sogenannten „Solution-Shearing“ Methode – eine Abscheidetechnik, die über die Kontrolle eines trocknenden Meniskus hochkristalline und ausgerichtete Schichten erzeugen kann – ist es möglich Dünnschichtbauelemente mit abgeschätzten, intrinsischen Ladungsträgermobilitäten von bis zu 12 cm²/Vs zu erzeugen. Um diese hoch-qualitativen Filme für die Herstellung von leistungsfähigen Transistoren zu nutzen, werden mehrere relevante Parameter betrachtet, darunter die Kanallänge, der Kontaktwiderstand und das Gate-Dielektrikum. Im Speziellen wird die Abscheidung des Dielektrikums mittels der „Solution-Shearing“ Methode untersucht. Es kann gezeigt werden, dass dies für die Herstellung von qualitativ hochwertigen Filmen mit Kapazitäten bis zu 280 nF/cm² genutzt werden kann. Angewendet in OFETs erlauben diese Schichten den Betrieb bei sehr geringen Spannungen von -1V. Um die Transkonduktanz der Transistoren zu erhöhen wird zudem eine mit der „Solution-Shearing“ Methode kompatible Source/Drain-Strukturierungsmethode untersucht. Diese ermöglicht Kanallängen unter einem Mikrometer und konnte hier für die Herstellung von funktionierenden Transistoren mit einer Kanallänge bis zu nur 500 nm angewendet werden. Eine der limitierenden Transistorkenngrößen ist der Kontaktwiderstand, wie durch die abweichende Skalierung des Stromes mit verringerter Kanallänge deutlich wird. Aus diesem Grund wurde auch die Grenzfläche zwischen Halbleiter und Source/Drain-Kontakten näher untersucht. Allerdings verbleibt die Entwicklung einer effektiven Methode zur Reduzierung des Kontaktwiderstandes ein Projekt für zukünftige Untersuchungen, auch wenn die vorliegende Arbeit einige wichtige Anhaltpunkte für mögliche Strategien liefert. Als wichtiges erstes Resultat liefert die vorliegende Arbeit eine Beschreibung zur Herstellung funktionsfähiger Kurzkanal-OFETs mittels „Solution-Shearing“, deren volles Potential aber in der Zukunft weiter untersucht werden muss.

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<div>Silicon based semiconductor technology is facing more and more challenges to continue the Moore's law due to its fundamental scaling limitations. To continue the pace of progress of device performance for both logic and memory devices, researchers are exploring new low-dimensional materials, e.g. nanowire, nanotube, graphene and hexagonal boron nitride. Transition metal dichalcogenides (TMDs) are attracted considerable attention due their atomically thin nature and proper bandgap at the initial study. Recently, more and more interesting properties are found in these materials, which will bring out more potential usefulness for electronic applications. Competing with the silicon device performance is not the only goal in the potential path finding of beyond silicon. Low-dimensional materials may have other outstanding performances as an alternative materials in many application realms. </div><div><br></div><div>This thesis explores the potential of TMD based devices in memory and logic applications. For the memory application, TMD based vertical devices are fully studied. Two-terminal vertical transition metal dichalcogenide (TMD) based memory selectors were firstly built and characterized, exhibiting better overall performance compared with some traditional selectors. Polymorphism is one of unique properties in TMD materials. 2D phase engineering in TMDs attracted great attention. While electric switching between semiconductor phase to metallic phase is the most desirable. In this thesis, electric field induced structural transition in MoTe₂ and Mo_1-xW_xTe₂ is firstly presented. Reproducible bipolar resistive random access (RRAM) behavior is observed in MoTe₂ and Mo_1-xW_xTe₂ based vertical devices. Direct confirmation of a phase transition from a 2H semiconductor to a distorted 2H_d metallic phase was obtained after applying an electric field. Set voltage is changed with flake thickness, and switching speed is less than 5 ns. Different from conventional RRAM devices based on ionic migration, the MoTe₂-based RRAMs offer intrinsically better reliability and control. In comparison to phase change memory (PCM)-based devices that operate based on a change between an amorphous and a crystalline structure, our MoTe₂-based RRAM devices allow faster switching due to a transition between two crystalline states. Moreover, utilization of atomically thin 2D materials allows for aggressive scaling and high-performance flexible electronics applications. Both of the studies shine lights on the new application in the memory field with two-dimensional materials.<br></div><div><br></div><div>For the logic application, the ultra thin body nature of TMDs allows for more aggressive scaling compared with bulk material - silicon. Two aspects of scaling properties in TMD based devices are discussed, channel length scaling and channel width scaling. A tunability of short channel effects in MoS₂ field effect transistor (FET) is reported. The electrical performance of MoS₂ flakes is governed by an unexpected dependence on the effective body thickness of the device which in turn depends on the amount of intercalated water molecules that exist in the layered structure. In particular, we observe that the doping stage of a MoS₂ FET strongly depends on the environment (air/vacuum). For the channel width scaling, the impact of edge states in three types of TMDs, metallic T_d-phase WTe₂ as well as semiconducting 2H-phase MoTe₂ and MoS₂ were explored, by patterning thin flakes into ribbons with varying channel widths. No obvious charge depletion at the edges is observed for any of these three materials, which is different from what has been observed in graphene nanoribbon devices. </div>

The objective of this work is to provide a comprehensive analysis of the small-signal and broadband noise performance of highly scaled silicon-based field-effect transistors (FETs), and develop high-frequency noise models for robust radio frequency (RF) circuit design. An analytical RF noise model is developed and implemented for scaled Si-CMOS devices, using a direct extraction procedure based on the linear two-port noise theory. This research also focuses on investigating the applicability of modern CMOS technologies for extreme environment electronics. A thorough analysis of the DC, small-signal AC, and broadband noise performance of 0.18 um and 130 nm Si-CMOS devices operating at cryogenic temperatures is presented. The room temperature RF noise model is extended to model the high-frequency noise performance of scaled MOSFETs at temperatures down to 77 K and 10 K. Significant performance enhancement at cryogenic temperatures is demonstrated, indicating the suitability of scaled CMOS technologies for low temperature electronics. The hot-carrier reliability of MOSFETs at cryogenic temperatures is investigated and the worst-case gate voltage stress condition is determined. The degradation due to hot-carrier-induced interface-state creation is identified as the dominant degradation mechanism at room temperature down to 77 K. The effect of high-energy proton radiation on the DC, AC, and RF noise performance of 130 nm CMOS devices is studied. The performance degradation is investigated up to an equivalent total dose of 1 Mrad, which represents the worst case condition for many earth-orbiting and planetary missions. The geometric scaling of MOSFETs has been augmented by the introduction of novel FET designs, such as the Si/SiGe MODFETs. A comprehensive characterization and modeling of the small-signal and high-frequency noise performance of highly scaled Si/SiGe n-MODFETs is presented. The effect of gate shot noise is incorporated in the broadband noise model. SiGe MODFETs offer the potential for high-speed and low-voltage operation at high frequencies and hence are attractive devices for future RF and mixed-signal applications. This work advances the state-of-the-art in the understanding and analysis of the RF performance of highly scaled Si-CMOS devices as well as emerging technologies, such as Si/SiGe MODFETs. The key contribution of this dissertation is to provide a robust framework for the systematic characterization, analysis and modeling of the small-signal and RF noise performance of scaled Si-MOSFETs and Si/SiGe MODFETs both for mainstream and extreme-environment applications.