abstract: The increased use of commercial complementary metal-oxide-semiconductor (CMOS) technologies in harsh radiation environments has resulted in a new approach to radiation effects mitigation. This approach utilizes simulation to support the design of integrated circuits (ICs) to meet targeted tolerance specifications. Modeling the deleterious impact of ionizing radiation on ICs fabricated in advanced CMOS technologies requires understanding and analyzing the basic mechanisms that result in buildup of radiation-induced defects in specific sensitive regions. Extensive experimental studies have demonstrated that the sensitive regions are shallow trench isolation (STI) oxides. Nevertheless, very little work has been done to model the physical mechanisms that result in the buildup of radiation-induced defects and the radiation response of devices fabricated in these technologies. A comprehensive study of the physical mechanisms contributing to the buildup of radiation-induced oxide trapped charges and the generation of interface traps in advanced CMOS devices is presented in this dissertation. The basic mechanisms contributing to the buildup of radiation-induced defects are explored using a physical model that utilizes kinetic equations that captures total ionizing dose (TID) and dose rate effects in silicon dioxide (SiO2). These mechanisms are formulated into analytical models that calculate oxide trapped charge density (Not) and interface trap density (Nit) in sensitive regions of deep-submicron devices. Experiments performed on field-oxide-field-effect-transistors (FOXFETs) and metal-oxide-semiconductor (MOS) capacitors permit investigating TID effects and provide a comparison for the radiation response of advanced CMOS devices. When used in conjunction with closed-form expressions for surface potential, the analytical models enable an accurate description of radiation-induced degradation of transistor electrical characteristics. In this dissertation, the incorporation of TID effects in advanced CMOS devices into surface potential based compact models is also presented. The incorporation of TID effects into surface potential based compact models is accomplished through modifications of the corresponding surface potential equations (SPE), allowing the inclusion of radiation-induced defects (i.e., Not and Nit) into the calculations of surface potential. Verification of the compact modeling approach is achieved via comparison with experimental data obtained from FOXFETs fabricated in a 90 nm low-standby power commercial bulk CMOS technology and numerical simulations of fully-depleted (FD) silicon-on-insulator (SOI) n-channel transistors. / Dissertation/Thesis / Ph.D. Electrical Engineering 2011

abstract: Radiation-induced gain degradation in bipolar devices is considered to be the primary threat to linear bipolar circuits operating in the space environment. The damage is primarily caused by charged particles trapped in the Earth's magnetosphere, the solar wind, and cosmic rays. This constant radiation exposure leads to early end-of-life expectancies for many electronic parts. Exposure to ionizing radiation increases the density of oxide and interfacial defects in bipolar oxides leading to an increase in base current in bipolar junction transistors. Radiation-induced excess base current is the primary cause of current gain degradation. Analysis of base current response can enable the measurement of defects generated by radiation exposure. In addition to radiation, the space environment is also characterized by extreme temperature fluctuations. Temperature, like radiation, also has a very strong impact on base current. Thus, a technique for separating the effects of radiation from thermal effects is necessary in order to accurately measure radiation-induced damage in space. This thesis focuses on the extraction of radiation damage in lateral PNP bipolar junction transistors and the space environment. It also describes the measurement techniques used and provides a quantitative analysis methodology for separating radiation and thermal effects on the bipolar base current. / Dissertation/Thesis / M.S. Electrical Engineering 2011

Ces travaux de thèse traitent de la modélisation d’un interrupteur bipolaire commandable monolithique bidirectionnel en tension et en courant et s’inscrivent dans la gestion de l’énergie dans l’habitat. L’objectif est de concevoir un interrupteur à faible perte énergétique capable de s’intégrer au sein d’une électronique de commande intelligente.Ces travaux s’intéressent dans un premier temps aux différentes solutions existantes destinées à notre application. A travers cette étude, on présente ainsi les avantages et les inconvénients des interrupteurs discrets ou encore des solutions monolithiques. On s’intéresse ensuite à l’étude d’un transistor bipolaire de puissance symétrique vertical. A l’aide de simulations par éléments finis, une étude bidimensionnelle et statique a permis de valider sa fonctionnalité à savoir son aptitude à fonctionner sous le réseau alternatif domestique. L’étude se concentrera ensuite sur les différentes technologies destinées à l’améliorer. En optant pour des caissons fortement dopés judicieusement placés au niveau de la base, il est démontré que les performances d’un tel composant peuvent être augmentées grâce au phénomène d’autoblindage. Finalement, dans le but de simplifier la réalisation de cet interrupteur, la technologie du RESURF sur SOI a été retenue. La structure, latérale, a ensuite été étudiée grâce à des simulations statiques bidimensionnelles puis tridimensionnelles qui ont mis en valeur l’intérêt de cette technologie tant au niveau de la conception qu’au niveau de la réalisation de la structure. / This study deals with the modeling of a monolithic switch bidirectional in current and voltage with full turn-off control for household appliances. The goal is to design a low losses switch which can be integrated to smart electronics functions. These works are focused, first, on discrete and monolithic existing solutions designed for such appliances before pointing out their main advantages and drawbacks. Monolithic structures are preferred over discrete ones thanks to their easiness to be integrated among other structures on the same substrate. The study is focused then on a vertical and symmetrical power bipolar transistor. 2D static simulations in finite elements performed on the structure confirm its ability to work on the mains. Further studies underline the possibility to improve it. By implementing around the active base heavily doped caissons which create a shielding effect, one can increase the structure performances. Finally, to simplify the switch processing steps, SOI RESURF technology is chosen. The lateral structure is studied thanks to 2D and 3D simulations which emphasize the benefits of such technology on both its design and manufacturing process.

Though the concept of junctionless field effect transistor (JLFET) is old, it was not possible to fabricate a useful JLFET device, as it requires a very shallow channel region. Very recently, the emergence of new and advanced technologies has made it possible to create viable JLFET devices using nanowires. This work aims to computationally investigate the interplay of quantum size-quantization and random dopant fluctuations (RDF) effects in nanoscale JLFETs. For this purpose, a 3-D fully atomistic quantum-corrected Monte Carlo device simulator has been integrated and used in this work. The size-quantiza¬tion effect has been accounted for via a param¬eter-free effec¬tive potential scheme and benchmarked against the NEGF approach in the ballistic limit. To study the RDF effects and treat full Coulomb (electron-ion and electron-electron) interactions in the real-space and beyond the Poisson picture, the simulator implements a corrected-Coulomb electron dynamics (QC-ED) approach. The essential bandstructure and scattering parameters (energy bandgap, effective masses, and the density-of-states) have been computed using an atomistic 20-band nearest-neighbour sp3d5s* tight-binding scheme. First, an experimental device was simulated to evaluate the validity of the simulator. Because of the small dimension, quantum mechanical confinement was found to be the dominant mechanism that significantly degrades the current drive capability of nanoscale JLFETs. Surface roughness scattering is not as prominent as observed in conventional MOSFETs. Also, because of its small size, the performance of the device is prone to the effect of variability, for which a discrete doping model was proved essential. Finally, a new JLFET was designed and optimized in this work. The proposed device is based on a gate-all-around silicon nanowire. Source/drain length is 32.5 nm and channel length is 14 nm. Gate contact length is 9 nm. The EOT (equivalent oxide thickness) is 1 nm. It has a metal gate with a workfunction of 4.55 eV. The source, channel and drain regions are n-type with a doping density of 1.5×1019 cm-3. Detailed simulation shows that the two most influential mechanisms that degrade the drive capability are quantum mechanical confinement and Coulomb scattering. Surface roughness scattering is found to be very weak. In addition, thinner nanowire is more prone to Coulomb scattering exhibiting a reduced ON-current (ION). Simulation results show that silicon nanowires with a side length (width and depth) of 3 nm and a doping density of 1.5×1019 cm-3 produce satisfactory drive current.

Submitted by Gabriel Leonardo Nogueira (gabrielnogueira5@hotmail.com) on 2016-11-02T14:46:19Z No. of bitstreams: 1 Dissertação Gabriel FINAL corrigida.pdf: 3857264 bytes, checksum: 37885bf252f0c527d86237d787b4fe47 (MD5) / Approved for entry into archive by Felipe Augusto Arakaki (arakaki@reitoria.unesp.br) on 2016-11-10T12:25:58Z (GMT) No. of bitstreams: 1 nogueira_gl_me_prud.pdf: 3857264 bytes, checksum: 37885bf252f0c527d86237d787b4fe47 (MD5) / Made available in DSpace on 2016-11-10T12:25:58Z (GMT). No. of bitstreams: 1 nogueira_gl_me_prud.pdf: 3857264 bytes, checksum: 37885bf252f0c527d86237d787b4fe47 (MD5) Previous issue date: 2016-08-26 / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / O transistor orgânico de efeito de campo com arquitetura vertical (VOFET) possibilita contornar as principais limitações de um transistor orgânico de efeito de campo (OFET) convencional. Nesta estrutura, as camadas são empilhadas verticalmente, de modo que os eletrodos de fonte e dreno são separados pela camada semicondutora e o comprimento do canal definido pela espessura do filme semicondutor. Para o VOFET proposto, utilizou-se Al e Al2O3 (obtido por anodização) como eletrodo e dielétrico de gate, respectivamente. O filme semicondutor foi obtido pela deposição por spincoating de P3HT dissolvido em clorofórmio. Os eletrodos de fonte e dreno foram obtidos por evaporação térmica a vácuo. Ao utilizar Al e Au como fonte e dreno, respectivamente, foi possível estudar os dispositivos de dois terminais que compõe o VOFET. Com base nesses dispositivos, importantes parâmetros da estrutura vertical foram determinados, como capacitância do dielétrico (~265 nF/cm2), densidade de portadores e mobilidade do P3HT (NA = 9,2 x 1016 cm-3 e μ = 1,5x10-4 cm2V-1s-1). Para utilizar Sn como eletrodo de fonte, o filme foi avaliado por meio de medidas de resistência e capacitância, aliadas à analise morfológica por AFM. Observa-se que a adição de uma camada de PMMA sobre o Al2O3 melhora o desempenho do VOFET. Para o VOFET formado por Al2O3/PMMA (20 nm/14 nm), com Sn e Al como fonte e dreno, foram calculados os valores de densidade de corrente (Jeff = 7x10-3 mA/cm2), voltagem e campo limiar (VTH = -8V e ELIMIAR = 330 MV/m). Com isso, foi obtido um VOFET utilizando filme de Sn evaporado como eletrodo de fonte perfurado. / A way of circumvent the limitations of conventional organic field-effect transistor (OFET), is by using the vertical organic field-effect transistor (VOFET). In this structure, with layers stacked vertically, the semiconductor is sandwiched between source and drain electrodes, where the channel length is determined by the thickness of the semiconductor film. In this study, we report a VOFET with Al and Al2O3 (obtained by anodization) as electrode and dielectric of gate, respectively. The semiconductor film was obtained by spin-coating of the P3HT in chloroform. We obtained the source and drain electrodes by vacuum thermal evaporation. The use of Al and Au as source and drain, respectively, enabled the investigation of the two devices contained in the VOFET (MIM capacitor, Schottky diode and MIS capacitor). Important parameters were determinate, as dielectric capacitance (~265 nF/cm2), charrier density and mobility of P3HT (NA = 9,2 x 1016 cm-3 e μ = 1,5x10-4 cm2V-1s-1), etc. To use Sn as source electrode, the film (by evaporation) was investigated by measurements of resistance and capacitance, combined with morphological analysis by AFM. We observed that the addiction of PMMA layer on Al2O3 improves the performance of VOFET. For VOFET obtained by using Al2O3/PMMA (20 nm/14 nm) as dielectric layer, with Sn and Al as source and drain, respectively, were calculate the values of current density (Jeff = 7x10-3 mA/cm2), threshold voltage and electric field (VTH = -8V e ETH = 330 MV/m). Thereat, we obtained a VOFET by evaporation of a thin film of Sn as perforated source electrode. / FAPESP: 2013/26973-5

Organic electronics are devices based on semiconductors derived from carbon based molecules and polymers. These devices can be made flexible, lightweight and potentially inexpensive with the development of economies of scale. Specific examples of organic electronics include organic thin-film transistors (OTFTs), organic light-emitting diodes (OLEDs) and organic photovoltaic (OPVs). Anthracene-based semiconductors are materials that have generated great interest primarily because of their structural planarity, potential for strong intermolecular interactions, air stability and ideal frontier molecular orbital energy levels. In this thesis, we detail two publications that examined functionalized anthracene molecules integrated into OTFTs, along with their thermal, electrochemical and optical properties. We started by examining seven novel 9,10-anthracene-based molecules. It was found that functionalization of the 9,10-positions with different phenyl derivatives resulted in negligible variation in the optical properties with minor (±0.10 eV) changes in electrochemical behaviour, while the choice of phenyl derivative greatly affected the thermal stability whereby the decomposition temperatures (Td) varied by as much as 128 °C between certain functionalized derivatives. The findings suggested that functionalization of the 9,10-position of anthracene leads to an effective handle for tuning of the thermal stability while having little to no effect on the optical properties and the solid-state arrangement. We continued with the synthesis of several novel anthracene derivatives which were di-substituted at the 2,6-positions. It was found that 2,6-functionalization with various fluorinated phenyl derivatives led to negligible changes in the optical behaviour while influencing the electrochemical properties (±0.10 eV). Furthermore, the choice of fluorinated phenyl moiety had noticeable effects on melting point and thermal stability (ΔTm < 55 °C and ΔTd < 65 °C). OTFTs were fabricated and characterized using the 2,6-anthracene derivatives as the semiconducting layer. The addition of fluorine groups on the phenyl groups led to a transition from p-type behaviour to n-type behaviour in BGBC OTFTs. The results indicated that the choice of functional group as well as its functionalization location, at the 9,10- and 2,6-positions, can act as powerful handles to engineer high performance OTFTs.

京都大学 / 新制・課程博士 / 博士(工学) / 甲第23210号 / 工博第4854号 / 新制||工||1758(附属図書館) / 京都大学大学院工学研究科電子工学専攻 / (主査)教授 白石 誠司, 教授 木本 恒暢, 教授 引原 隆士 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DGAM

Nanoscale materials are not new in either nature or physics. However, the recent technological improvements have given scientists new tools to understand and quantify phenomena that occur naturally due to quantum confinement effects. In general, these phenomena induce remarkable optical, magnetic, and electronic properties in nanoscale materials in contrast to their bulk counterpart. In addition, scientists have recently developed the necessary tools to control and exploit these properties in electronic devices, in particular field effect transistors, magnetic memories, and gas sensors. In the present thesis we implement theoretical and computational tools for analyzing the ground state and electronic transport properties of nanoscale materials and their performance in electronic devices. The ground state properties are studied within density functional theory using the SIESTA code, whereas the transport properties are investigated using the non-equilibrium Green's functions formalism implemented in the SMEAGOL code. First we study Si-based systems, as Si nanowires are believed to be important building blocks of the next generation of electronic devices. We derive the electron transport properties of Si nanowires connected to Au electrodes and their dependence on the nanowire growth direction, diameter, and length. At equilibrium Au-nanowire distance we find strong electronic coupling between electrodes and nanowire, resulting in low contact resistance. For the tunneling regime, the decay of the conductance with the nanowire length is rationalized using the complex band structure. The nanowires grown along the (110) direction show the smallest decay and the largest conductance and current. Due to the high spin coherence in Si, Si nanowires represent an interesting platform for spin devices. Therefore, we built a magnetic tunneling junction by connecting a (110) Si nanowire to ferromagnetic Fe electrodes. We have find a substantial low bias magnetoresistance of ~ 200%, which halves for an applied voltage of about 0.35 V and persist up to 1 V. In order to account for shallow impurities coming from bulk Si, the nanowire is doped with either P or B atoms (n or p type). Doping in general decreases the magnetoresistance as soon as the conductance is no longer dominated by tunneling. On the other hand, we study the electron transport properties of Si nanotubes connected to Au electrodes. The general properties turn out to be largely independent of the nanotube chirality, diameter, and length. However, the tunneling conductance of Si nanotubes is found to be significantly larger than in Si nanowires, while having a comparable band gap. For this reason we simulate a Si nanotube field effect transistor by applying an uniform potential gate. Our results demonstrate very high values of the transconductance, outperforming the best commercial Si field effect transistors, combined with low values of the subthreshold swing. Phosphorene (monolayer black P) is the only elemental two-dimensional material besides graphene that can be mechanically exfoliated and also can support electronics. Specific dislocations of the atoms in the phosphorene lattice generate another stable two-dimensional allotrope with buckled honeycomb lattice, blue P. We demonstrate structural stability of monolayer zigzag and armchair blue P nanotubes by means of molecular dynamics simulations. The vibrational spectrum and electronic band structure are determined and analyzed as functions of the tube diameter and axial strain. The nanotubes are found to be semiconductors with a sensitive indirect band gap that allows flexible tuning. We study the adsorption of CO, CO2, NH3, NO, and NO2 molecules on blue P nanotubes. They are found to surpass the gas sensing performance of other nanoscale materials. Investigations of the gas adsorption and induced charge transfer indicate that blue P nanotubes are highly sensitive to N-based molecules, in particular NO2, due to covalent bonding. The current-voltage characteristics of nanotubes connected to Au electrodes is used to evaluate the change in resistivity upon adsorption. The observed selectivity and sensitivity properties make blue P nanotubes superior gas sensors for a wide range of applications. Using black P and blue P nanoribbons, we configure field effect transistors with atomically perfect junctions by using armchair nanoribbons as semiconducting channel and zigzag nanoribbons as metallic leads. We characterize the devices and observe a performance superior to Si-based devices, with on/off ratio of ~ 103, low subthreshold swing of ~ 60 mV/decade, and high transconductance of ~ 104 S/m.

Over the past few decades, metal phthalocyanines (MPcs) have been thoroughly investigated as active materials in organic field-effect transistors (OFETs) towards the commercialization of flexible integrated circuits and displays. One of several advantages to MPcs as building blocks for OFETs is the high degree of functionality, from which the choice of metal ion, substituents along with the phthalocyanine framework and axially bound ligands can synergistically tune the physical and self-assembly properties of the material. Recent interest has been directed to the introduction of main-group elements as the central ion of MPcs as an avenue to install both hole and electron transport properties and improve device performance. To prepare materials that are suitable to be employed as the semiconducting active layer in organic field-effect transistors, a family of novel silicon phthalocyanine derivatives was prepared. The synthesis and optoelectronic properties of those new axially disubstituted silicon phthalocyanines are detailed in this work. Axial ligand variation mainly includes alkylsiloxy derivatives. The emphasis of the current thesis, however, is on tailoring the Pc backbone, which includes replacing the four benzene units with pyrazine moieties, extending the degree of conjugation with naphthalene, and introducing substituents on their peripheral positions. Several metal-containing tetra-2,3-pyrazinoporphyrazines are also described, but their applications are limited due to the difficulty of purification. Specifically, Chapter 1 serves as a comprehensive review of main-group phthalocyanines and their use as active materials in organic field-effect transistors. In Chapter 2, silicon tetra-2,3-pyrazinoporphyrazine complexes are explored. The isosteric substitution of CH groups in Pc macrocycle for nitrogen atoms leads to an obvious hypsochromic shift in their main absorption band, and their relatively low energy levels make them promising air-stable n-type organic semiconducting materials for OFETs. The synthesis and characterization of silicon tetra(tert-butyl)-2,3-naphthalocyanine complexes are described in Chapter 3. The extension of π-conjugation leads to obvious bathochromic shifts in the main absorption band. In addition, the introduction of tert-butyl groups on the periphery of the molecule reduces the tendency of the naphthalocyanine molecules to aggregate, thereby increase their solubility. Chapter 4 covers the synthesis and characterization of zinc tetra-2,3-pyrazinoporphyrazine and cobalt tetra-2,3-pyrazinoporphyrazine, whereas more future works are expected. The fifth chapter provides a conclusion to this work, and possible future directions of the research conducted herein.

In this thesis I will evaluate few discrete devices and their differences in structure, static and switching characteristics and also some structurall and manufacturing principles. After that I will follow up with their integration into power modules , where I will also aim on construction solutions and trends. These power moduls are today delivered as „stack“ or „system“, where for optimization and highest achievable efficiency of the whole unit the integration of protection, drive and cooloing stage is incorporated. Cooling and drive of some devices will be subject of a separate chapter. Also some of novel materials, which are very promissing, will be introduced. They show improvemnet in electrical and thermal properties. They have potential to replace the currently dominant Silicon in the near future.