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This thesis describes the use of charge modulation spectroscopy to investigate the negative and positive charge-induced absorptions in conjugated semiconducting polymers as a way to experimentally compare the wavefunctions of electrons and holes. Interactions between light and charges including fluorescence quenching and photocurrent are also explored. Conjugated polymers have an electronic structure with an energy gap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO). In the neutral ground state, there are no optical transitions at photon energies lower than this gap. When an excess charge is added to a conjugated polymer, the charge couples with a local structural reorganisation forming a localised entity known as a polaron. The polaron has two new electronic states within the energy gap symmetrically spaced about the midgap energy. Typically two new optical transitions between the polaronic states are allowed and can be accessed with sub gap energies. In order to probe the sub gap polaron absorptions charges can be added by electrical injection. Electrical injection in a transistor configuration provides a controlled way to measure the absorption of a known number of charges in the solid state and without triplet or singlet absorptions complicating the spectra as observed in photo-induced absorption. By taking advantage of recently developed ambipolar transistors where both holes and electrons can be accumulated in the same device a comparison can be made between the negative and positive polaron wavefunctions. Two polyfluorene polymers were chosen as examples where quantum chemical calculations predict either the same or different wavefunctions for the electron and hole. Poly(9,9-di-n-octylfluorene) (F8) is a hydrocarbon-only polymer which is expected to have similar electron and hole wavefunctions, whereas the related co-polymer, poly(9,9-di-n-octylfluorene-alt-benzothiadiazole) (F8BT) is expected to have an electron wavefunction that is more localized that the hole. The ambipolar transistors used in this thesis are typified by a dominant contact resistance which introduces difficulties in the charge modulation spectroscopy experiment. New techniques for simultaneous electrical and optical characterisation are developed and new device structures and fabrication processes are introduced in order to overcome a number of artifacts and improve the accuracy of the measurement allowing quantitative comparisons to be made. The increase in transistor or diode current with energy gap illumination and the quenching of fluorescence in the presence of charges is also investigated and a new method for imaging charge trapping and device operation in transistors with luminescent semiconductors is introduced.

La montée en fréquence des composants électroniques conventionnels tels que les HEMT, grâce aux règles de changement d'échelle, atteint ses limites. C'est dans ce contexte qu'il est intéressant de développer des composants d'architecture différente, comme les dispositifs balistiques, dont les dimensions sont de l'ordre du libre parcours moyen à température ambiante. Cette étude s'inscrit dans l'optimisation technologique et la caractérisation électrique de composants balistiques de la filière InGaAs/lnAlAs pseudomorphique sur substrat d'InP. Les propriétés nonlinéaires des jonctions balistiques à trois branches (TBJ) basées sur une hétérostructure optimisée ont été caractérisées en régime statique. Le fonctionnement des TBJ en redresseur de tension et en doubleur de fréquence a été étudié en hyperfréquence. Une sensibilité de redressement de 0.022mV/µW à 94 GHz en l'absence de polarisation a été obtenue sur des dispositifs à deux jonctions balistiques en parallèle. Le doublement de la fréquence dans le domaine de fonctionnement non linéaire du TBJ a été observé pour un signal sinusoïdal d'entrée à 4GHz, la tension alternative mesurée dans la branche centrale correspondant essentiellement à l'harmonique d'ordre deux à 8GHz. Enfin, des TBJ avec une grille Schottky ont été fabriqués et caractérisés en inverseurs de courant jusqu'à 400kHz. Leur fonctionnement en transistor a été mesuré en hyperfréquences. Une fréquence fT de 30GHz a été obtenue sur un composant dont la largeur de branche sous la grille est 200nm. / The increase of speed in conventional electronic devices, such as in HEMT, with down-scale rules, is reaching limitations. That is why it is interesting to develop devices with a new design such as ballistic devices which have dimensions around the electron me an free path at room temperature. The aim of this study is the technological optimisation and the electrical characterisation of InGaAs/lnAIAs pseudomorphic InP-based ballistic devices. Nonlinear properties of three-terminal ballistic junctions (TBJ) fabricated using an optimised heterostructure have been studied in DC mode. TBJ, which are operating as rectifiers and frequency multipliers, have been characterised in high frequency. A rectifying sensitivity of O.022mV/µW at 94GHz, without a DC bias, has been obtained on devices with two junctions integrated in parallel. Frequency doubling in the nonlinear domain has been shown with an applied sinusoidal signal of 4GHz. voltage measured in the output branch corresponding essentially to the second harmonie at 8GHz. Finally, TBJ with a Schottky gate have been tàbricated and their property of current inversion has been characterised up to 400kHz. Their transistor behaviour has been measured in microwaves. A current gain eut-off frequency fT of 30GHz has been obtained for a device with a branch width under the gate of 200nm.

M.Ing. (Electrical & Electronic Engineering) / The technology of the use of electronic devices as power switches is still being developed. Because of the increasing demand for low mass and cost, the switching frequency must be as high as possible. The limiting factor for the frequency is the energy loss which is dissipated in the semiconductor crystal during each switching-transient. If tllis switching loss can be reduced, a higher frequency can be obtained. The switching loss is due to the non-instantaneous switching process of the semiconductor device. For the reduction of this switching loss, the device must be switched as fast as possible via its control-electrode. Further improvement can be obtained through the use of snubber networks. This thesis considers the bipolar high-voltage transistor as a power switch. The unfavourable switching loci of the transistor- switch is discussed in chapter 1. In chapter 2 the basedrive during transistor turn-off is investigated, in order to reduce the turn-off time. The following chapters de;al with the use of snubber circuits, which relieve the transistor during turn-on and turn-off. The advantages, as well as the disadvantages and limitations of snubbers are discussed. After the linear turn-off and turn-on snubbers have been treated, the non-linear turn-on snubber, which uses a saturable inductor, will be considered from an experimental point of view. The results show that this snubber is very effective in relieving the transistor during turn-on. In chapter 7 the non-linear turn-off snubber is treated on an experimental as well as on a mathematical bas e . Cri teria, which must be satisfied for realisation of a practical nonlinear capacitor, is also laid down. Because of the fact that a first order snubber is always loading the transistor during the complimentary switchin,]-transient, chapter 8 deals with a second order snubber, which consists of both a capacitor and an inductor. Experimentally it was found that the turn-on time is reduced with the use of a turn-on snubber, while the turn-off time is increased with the use of a turn-off snubber. In chapter 9 the physical behaviour of the switching processes is investigated, after which the influences of the snubbers on the switching times is explained qualitatively...

ZnO has generated interest for flexible electronics/optoelectronic applications including transparent thin film transistors (TFTs). For this application, low temperature processes that simultaneously yield good electrical conductivity and optical transparency and that are compatible with flexible substrates such as plastic, are of paramount significance. Further, gate oxides are a critical component of TFTs, and must exhibit low leakage currents and self-healing breakdown in order to ensure optimal TFTs switching performance and reliability. Thus, the objective of this work was twofold: (1) develop an understanding of the processing-structure-property relationships of ZnO and high-κ BaTa2O6 and Al2O3 (2) understand the electronic defect structure of BaTa2O6 /ZnO and Al2O3/ZnO interfaces and develop insight to how such interfaces may impact the switching characteristics (speed and switching power) of TFTs featuring these materials. Of the ZnO films grown by atomic layer deposition (ALD), pulsed laser deposition (PLD) and magnetron sputtering at 100-200 °C, the latter method exhibited the best combination of n-type electrical conductivity and optical transparency. These determinations were made using a combination of photoluminescence, photoluminescence excitation, absorption edge and Hall measurements. Metal-insulator-semiconductor devices were then fabricated with sputtered ZnO and high-κ BaTa2O6 and Al2O3 and the interfaces of high-κ BaTa2O6 and Al2O3 with ZnO were analyzed using frequency dependent C-V and G-V measurements. The insulator films were deposited at room temperature by magnetron sputtering using optimized processing conditions. Although the Al2O3 films exhibited a lower breakdown strength and catastrophic breakdown behavior compared to BaTa2O6/ZnO interface, the Al2O3/ZnO interface was characterized by more than an order of magnitude smaller density of interface traps and interface trapped charge. The BaTa2O6 films in addition were characterized by a significantly higher concentration of fixed oxide charge. The transition from accumulation to inversion in the Al2O3 MIS structure was considerably sharper, and occurred at less than one tenth of the voltage required for the same transition in the BaTa2O6 case. The frequency dispersion effects were also noticeably more severe in the BaTa2O6 structures. XPS results suggest that acceptor-like structural defects associated with oxygen vacancies in the non-stoichiometric BaTa2O6 films are responsible for the extensive electrical trapping and poor high frequency response. The Al2O3 films were essentially stoichiometric. The results indicate that amorphous Al2O3 is better suited than BaTa2O6 as a gate oxide for transparent thin film transistor applications where low temperature processing is a prerequisite, assuming of course that the operation voltage of such devices is lower than the breakdown voltage. Also, the operation power for the devices with amorphous Al2O3 is lower than the case for devices with BaTa2O6 due to the smaller fixed oxide charges and interface trap density.

Emerging transparent conducting and semiconducting oxide (TCO) and (TSO) materials have achieved success in display markets. Due to their excellent electrical performance, TSOs have been chosen to enhance the performance of traditional displays and to evaluate their application in future transparent and flexible displays. This dissertation is devoted to the study ZnO-based thin film transistors (TFTs) using multilayer dielectrics and channel layers. Using multilayers to engineer transistor parameters is a new approach. By changing the thickness, composition, and sequence of the layers, transistor performance can be optimized. In one example, Al2O3/Ta2O5 bilayer gate dielectrics, grown by atomic layer deposition at low temperature were developed. The approach combined high dielectric constant of Ta2O5 and the excellent interface quality of Al2O3/ZnO, resulting in enhanced device performance. Using zinc oxide (ZnO)/hafnium oxide (HfO2) multilayer stack as a TFT channel with tunable layer thicknesses resulted in significant improvement in TFT stability. Atomic layer deposited SnO2 was developed as a gate electrode to replace ITO in thin film transistors and circuits. The SnO2 films deposited at 200 °C show low electrical resistivity of ~3.1×10-3 Ohm-cm with the high transparency of ~93%. TFT fabricated with SnO2 gate show excellent transistor properties. Using results from the above experiments, we have developed a novel process in which thin film transistors (TFTs) are fabricated using one binary oxide for all transistor layers (gate, source/drain, semiconductor channel, and dielectric). In our new process, by simply changing the flow ratio of two chemical precursors, C8H24HfN4 and (C2H5)2Zn, in an ALD system, the electronic properties of the binary oxide HZO were controlled from conducting, to semiconducting, to insulating. A complete study of HZO thin films deposited by (ALD) was performed. The use of the multi-layer (HfO2/ZnO) channel layer plays a key role in improving the bias stability of the devices. The low processing temperature of all materials at 160 °C is an advantage for the fabrication of fully transparent and flexible devices. After precise device engineering, including growth temperature, gate dielectric, electrodes (S/D&G) and semiconductor thickness, TFT with excellent device performance are obtained.

Since the discovery of organic semiconductors (OSCs) over four decades ago, the field of organic electronics has broken our misconceptions regarding the possibilities of modern electronics. The synthetic toolkit of organic chemistry enables the creation of a limitless number of unique OSCs that can be specifically tailored and engineered with the specific and desired properties for unique applications. The rapid adoption of modern information systems, “Internet of Things,” in which smart devices and sensors ubiquitously collect and exchange data has resulted in a need for low-cost sensors to be deployed everywhere from the monitoring of food supply chains, environmental conditions, to human health. Organic thin-film transistors (OTFTs) are a necessary component to support these technologies. However, their mass adoption will require reduction in cost and improved compatibility with low voltage generating printed batteries or flexible and ultrathin photovoltaics. This thesis is focused on the development of high performing solid state polymer electrolytes to be employed as the gating medium in OTFTs. The choice of conventional gating materials often leads to a tradeoff between high capacitance, operating speed and material softness. For example liquid electrolyte gating materials have high capacitance but low operating speed and are liquid at room temperature which is unacceptable for many electronics application. Polymer gating materials often have lower capacitance but fast operating conditions and solid at room temperature. In this thesis we establish structure property relationships which aid in the design of novel block copolymer-based gating materials which simultaneously enable the increase in capacitance and switching speed while remaining solid at room temperature. In the first study I established a styrene-based ionic liquid monomer can be using as a controlling monomer in the nitroxide mediated copolymerization of methacrylates. The second study then focuses on the integration of these materials into OTFT devices; the morphology (block vs random copolymers) effect on device performance is assessed. The last study builds on the findings of the previous study and further explores the structural elements of block copolymers on device performance. The work presented here outlines the development of advanced poly(ionic liquid) based solid electrolyte materials that enables both reduced operating voltages and fast switching. Finally, we establish structure-property relationships that relate the molecular architecture to OTFT device performance paving the way for the adoption of a new generation of high performing, printable and flexible electronics.

The purpose of this study is to design a transistor conversion system oriented toward quality categories rather than toward devices. Underlying this purpose are two working hypotheses: First, quality categories can be developed by capitalizing on transistor total quality and convertibility; second, a transistor conversion system oriented toward quality categories is superior to existing device-oriented methods.

The commercialization of wide band-gap devices such as silicon carbide and gallium nitride transistors has made it possible for power electronics applications to achieve unprecedented performance in terms of efficiency and power density. However, the device characteristics which make this performance possible also create secondary consequences in these high-performance applications. One such consequence which is particularly difficult to manage in the context of power electronics applications is the occurrence of self-sustained oscillation. This problem has been recognized in the power electronics literature, but heretofore has not received an extensive analytical treatment. This dissertation provides a comprehensive analytical treatment of the self-sustained oscillation phenomenon, logically separated into two components: an initial forced cycle and the subsequent oscillatory behavior. A large-signal model has been developed in order to predict the occurrence of the initial forced cycle based on a set of estimated initial conditions derived from a user-specified operating point. The establishment of the initial forced cycle as predicted by the large-signal model creates the bias conditions necessary for the analytical treatment of the subsequent oscillatory behavior. For this purpose, a small-signal model is presented which describes this phenomenon on the basis of recognizing the wide band-gap device and a minimal set of parasitic components associated with the gate and drain circuits as an unintended negative conductance oscillator. In the context of established oscillator design theory it has been shown both analytically and with simulation that negative differential conductance exhibited by the parasitic model explains the conditions under which self-sustained oscillation is likely to occur. Both the large-signal and small-signal models are shown to demonstrate good agreement with empirical results from pulsed switching experiments obtained over a wide range of operating conditions. In addition, a catalog of known solutions to the problem of self-sustained oscillation is presented, along with a discussion of a method by which the current work can be used by application designers to preclude the occurrence of this phenomenon in practical systems by design.

As science and medicine advance, it becomes ever more important to be able to control and analyze smaller and smaller bioparticles all the way down to single molecules. In this dissertation several studies aimed at improving our ability to manipulate and monitor single biomolecules will be discussed. First, we will discuss a study on developing a way to map dielectrophoresis with nanoscale resolution using a novel atomic force microscopy technique. Dielectrophoresis can be applied on nanoparticles through micron-scale electrodes to separate and control said particles. Therefore, this new method of mapping this force will greatly improve our ability to manipulate single biomolecules through dielectrophoresis. The next two studies discussed will be aimed at using carbon nanotube nanocircuits to monitor single protein kinetics in real time. Drug development and delivery methods rely on the precise understanding of protein interactions, thus creating the need for information on single protein dynamics that our techniques provides. The proteins studied in these sections are MMP1 and HDAC8, both of which are known targets of anti-cancer drugs. Finally, we developed a new strategy for diagnosing pancreatic cancer. Our strategy involves using graphene nanotransistors to detect exosomes released from the pancreatic tumor. The ability to reliably diagnose pancreatic cancer before it reaches metastasis would greatly improve the life expectancy of patients who develop this condition. We were able to test our technique on samples from a number of patients and were successfully able to distinguish patients with pancreatic cancer from noncancerous patients.