Le développement des transistors organiques, ces dernières années, a permis une nette amélioration de leurs performances et de leur stabilité. Ceci a été possible, notamment, grâce à une meilleure compréhension des mécanismes régissant le transport de charges dans ces dispositifs. Cependant, certains phénomènes restent encore à éclaircir, en particulier au niveau de l'interface entre le semi-conducteur et le diélectrique. Le piégeage des porteurs de charges qui est une des principales causes de perturbations du transport de charges dans les transistors organiques, en est un. Cette thèse se propose donc, d'étudier ce phénomène dans des transistors à base de pentacène.Les groupements polaires, et plus particulièrement les groupements hydroxyles, présents à l'interface entre l'isolant et le semi-conducteur, sont les principaux responsables du piégeage des porteurs de charges dans les transistors organiques. Afin de limiter leur présence, une technologie basée sur l'emploi d'une couche interfaciale diélectrique passivante, pauvre en groupements hydroxyles, à base de fluorure de calcium, a été mise en place. L'influence de cette couche sur le comportement de transistors à base de pentacène a été étudiée, de même que le vieillissement de ces dispositifs sous différentes conditions de stockage (sous vide et à l'air) et sous contrainte électrique.Ainsi, il a été mis en évidence qu'une couche de fluorure de calcium d'une épaisseur trop importante (de l'ordre de 5 nm) modifie la morphologie de la couche de pentacène, ce qui se traduit par une quasi-disparition du transport de charges dans le pentacène en configuration de transistor à effet de champ. Les études de vieillissement ont montré que sous l'effet de la couche interfaciale de CaF2, même d'une très fine épaisseur (de quelques nanomètres), une quantité plus importante d'humidité est présente dans la couche de pentacène, probablement à cause de la nature hygroscopique du fluorure de calcium.

At present the field of molecular electronics - also known as molecular semiconductors, organic semiconductors, plastic electronics or organic electronics - is dominated by organic materials, both polymeric and molecular, with much less attention being focused on transition metal based complexes despite the advantages they can offer. Such advantages include tuneable frontier orbitals through the ligand/metal interaction and the ability to generate stable paramagnetic species. Devices containing radical materials are particularly interesting in order to examine the interplay between conduction and spin - an effect which is not yet properly understood but can give rise to exotic behaviour. A series of homoleptic, bis-ligand Ni(II) and Cu(II) complexes were prepared using three structurally related phenolic oxime ligands, 2-hydroxy-5-t-octylacetophenone oxime (t-OctsaoH), 2-hydroxy-5-n-propylacetophenone oxime (n-PrsaoH) and 2- hydroxyacetophenone oxime (HsaoH). The complexes were characterised by single-crystal X-ray diffraction, cyclic voltammetry, UV/Vis spectroscopy, field-effect-transistor measurements, DFT/TD-DFT calculations and in the case of the paramagnetic species, EPR and magnetic susceptibility. Variation of the substituent on the ligand from t-octyl to n-propyl to H enabled electronic isolation of the complexes in the crystal structures of M(t-OctsaoH)2, which contrasted with π-stacking interactions observed in the crystal packing of M(n-PrsaoH)2 and of M(HsaoH) (M = Ni, Cu). This was further evidenced by comparing the antiferromagnetic interactions observed in samples of Cu(n-PrsaoH)2 and Cu(HsaoH)2 with the ideal paramagnetic behaviour for Cu(t-OctsaoH)2 down to 1.8 K. Despite isostructural single crystal structures for M(n-PrsaoH)2, thin-film X-ray diffraction and SEM revealed different morphologies depending on the metal and the deposition method employed. However, the complexes of M(n-PrsaoH)2 and M(HsaoH) failed to demonstrate significant charge transport in an FET device despite displaying the ability to form π- stacking structures. A series of planar Ni(II), Cu(II) and Co(II) dibenzotetraaza[14]annulenes (dbtaa) and dinapthotetraaza[14]annulenes (dntaa) were synthesised and studied crystallographically, optically, electrochemically and magnetically. Thin films of each of these complexes have been prepared by vacuum deposition to evaluate the field-effect transistor (FET) performance as well as the morphology and crystallinity of the film formed. Single crystal data revealed that Ni(dbtaa) and Cu(dbtaa) are isomorphous to each other, with Co(dbtaa) displaying a different crystallographic packing. The electrochemistry and UV/Vis absorption studies indicate the materials are redox active and highly coloured, with molar extinction coefficients as large as 80,000 M-1cm-1 in the visible region. The paramagnetic Cu(II) and Co(II) complexes display weak 1-dimensional antiferromagnetic interactions and were fit to the Bonner-Fisher chain model. The data revealed that the Co(II) species possesses much stronger magnetic exchange interactions compared with the Cu(II) complex. Each of the materials formed polycrystalline films when vacuum deposited and all showed ptype field-effect transistor behaviour, with modest charge carrier mobilities in the range of 10-5 to 10-9 cm2 V-1 s-1 . SEM imaging of the substrates indicates that the central metal ion, and its sublimation temperature, has a crucial role in defining the morphology of the resulting film. Structurally related Cu(II) and Ni(II) dithiadiazoletetraaza[14]annulene (dttaa) macrocycles were synthesised and studied in the context of their thin film electrochemical, conducting and morphological properties. Both the Ni(II) and Cu(II) complexes were found to be volatile under reduced pressure, which allowed crystals of both materials to be grown and the single crystal structures solved. Interestingly, the crystal packing of these heterocyclic macrocycles varies depending on whether the central metal ion is Cu(II) or Ni(II), which is in contrast to the analogous dibenzotetrazaannulenes complexes. Soluble Ni(II) analogues containing benzoyl groups on the meso- positions of the macrocycle (dttaaBzOR) were also prepared and contrasted with the insoluble Ni(dttaa) complexes in terms of their solution optical and electrochemical properties. Thin film electrochemical studies of Cu(dttaa) and Ni(dttaa) showed chemically reversible oxidative processes but on scanning to reductive potentials the films disintegrated almost immediately as the bulky counter tetrabutylammonium cation entered the thin film. FET studies undertaken on polycrystalline films of both complexes, using various device configurations and surface treatments, failed to realise any gate effect. Thin film XRD measurements indicate that films of both complexes formed by vacuum deposition are crystalline and contain a mixture of molecular alignments, with molecules aligning “edge on” and “face down” to the substrate. SEM imaging failed to effectively resolve the morphology of the films implying the sizes of the crystallites are small, which may help to explain the lack of FET effect. A series of bis-ligand diimine Ni, Cu and Pd complexes have been synthesised from the ligand 4,5-bis(dodecyloxy)benzene-1,2-diamine (dbdaH2). The same ligand was also used to prepare a series of soluble Cu(II) and Ni(II) tetraaza[14]annulene macrocycles. All the bis-ligand diimine complexes were found to suffer from instability in air due to the ease at which the complexes are oxidised. The Ni complex, Ni(dbda)2, was found to display a NIR transition in the region of 971 to 1024 nm depending on the polarity of the solvent that the molecule is dissolved in. Solution electrochemistry studies of Ni(dbda)2 reaffirmed the facile nature of the first oxidative process, with the HOMO energy calculated at -4 eV by hybrid-DFT. This compound failed to yield semiconducting behaviour in an FET device despite the use of surface treatments aimed at promoting suitable molecular alignment across the conducting channel.

There has been a remarkable progress in the development of organic electronic materials since the discovery of conducting polymers more than three decades ago. Many of these materials can be processed from solution, in the form as inks. This allows for using traditional high-volume printing techniques for manufacturing of organic electronic devices on various flexible surfaces at low cost. Many of the envisioned applications will use printed batteries, organic solar cells or electromagnetic coupling for powering. This requires that the included devices are power efficient and can operate at low voltages. This thesis is focused on organic thin-film transistors that employ electrolytes as gate insulators. The high capacitance of the electrolyte layers allows the transistors to operate at very low voltages, at only 1 V. Polyanion-gated p-channel transistors and polycation-gated n-channel transistors are demonstrated. The mobile ions in the respective polyelectrolyte are attracted towards the gate electrode during transistor operation, while the polymer ions create a stable interface with the charged semiconductor channel. This suppresses electrochemical doping of the semiconductor bulk, which enables the transistors to fully operate in the field-effect mode. As a result, the transistors display relatively fast switching (≤ 100 µs). Interestingly, the switching speed of the transistors saturates as the channel length is reduced. This deviation from the downscaling rule is explained by that the ionic relaxation in the electrolyte limits the channel formation rather than the electronic transport in the semiconductor. Moreover, both unipolar and complementary integrated circuits based on polyelectrolyte-gated transistors are demonstrated. The complementary circuits operate at supply voltages down to 0.2 V, have a static power consumption of less than 2.5 nW per gate and display signal propagation delays down to 0.26 ms per stage. Hence, polyelectrolyte-gated circuits hold great promise for printed electronics applications driven by low-voltage and low-capacity power sources.

In this work Scanning Kelvin Probe Microscopy (SKPM) was used to characterize surface states and device surface charging in nitride materials. Samples grown by Molecular Beam Epitaxy (MBE), Metal Organic Chemical Vapor Deposition (MOCVD) and Hydride Vapor Phase Epitaxy (HVPE) typically show a high surface band bending of about 1 eV. In an n-type sample with 3X1017 cm-3 carrier concentration, 1 eV upward band bending corresponds to 1.7X1012 cm-2 trapped charge density in the surface states. Under continuous ultraviolet (UV) illumination up to 0.6 eV surface photo voltage effect could be observed in some samples, which further indicates that surface band bending is very likely larger than 0.6 eV, i.e. close to 1 eV. Reactive Ion Etching (RIE)damage was observed to increase surface band bending by about 0.4 eV where as surface treatments in organic solvents and inorganic acids did not affect surface band bending significantly. These results indicate presence of high density of surface states in devices fabricated in nitride materials. Surface potential measurements immediately after turning off a reverse bias to the Schottky contact of a GaN Schottky diode as well as an AlGaN/GaN Hetero-junction Field Effect Transistor (HFET) show an increase of band bending near the Schottky contact edge. For an applied reverse bias of 4 V, about 0.5 eV increase of band bending was observed. This increase of band bending was caused by tunneling of electrons from the Schottky contact and their subsequent capture by surface states near the contact edge. In case of the HFET, the increase of band bending for a bias that caused no current flow through the device was similar to a bias that did. This showed that hot electron injection from the channel did not play a significant role in increasing surface band bending. The accumulated charge near the gate edge of a HFET can deplete the channel, which would cause the drain current to decrease. The total times of accumulation and dissipation of excess surface charge near the gate edge of the HFET were comparable to the time scales of drain current transients of current collapse and recovery. From this observation we attributed current collapse phenomena to charge accumulation near the edge of the reverse biased gate contact of a HFET.

Engineers know well from an early point in their training the trials and tribulations of having to make design tradeoffs in order to optimize one performance parameter for another. Discovering tradeoff conditions that result in the elimination of a loss associated with the enhancement of some other parameter (an improvement over a typical tradeoff), therefore, ushers in a new paradigm of design in which the constraints which are typical of the task at hand are alleviated. We call such a design paradigm “tuning” as opposed to “trading off”, and this is the central theme of this work. We investigate two types of microwave electronic devices, namely GaN-based heterostructure field effect transistors (HFETs) and tunable ferroelectric-ferrite-based microwave phase shifters. The “tuning” associated with these types of devices arises from the notion of an optimal 2DEG density, capable of achieving higher performance in terms of electron velocity and enhanced reliability in the case of the HFET, and the coupling of ferroelectric and ferrite materials in tunable microwave phase shifters, capable of achieving high differential phase shifts while at the same time mitigating the losses associated with impedance mismatching which typically arise when the phase is tuned. Promises and problems associated with HFET devices based on the intriguing InAlN/GaN material system will be described. We focus on the fundamental problem associated with the induction of the large density of carriers at the interface, namely the disintegration of an excess of longitudinal optical phonons (hot phonons) in the channel. We use microwave measurements in conjunction with stress tests to evidence the existence of an optimal 2DEG density wherein the hot phonon effect can be “tuned,” which allows for enhanced high frequency performance as well as device reliability. Next, we focus on the design, fabrication, and measurement of tunable phase shifters consisting of thin films of BaxSr1-xTiO3 (BST), which has the advantage of having high dielectric tunability as well as relatively low microwave loss. We discuss the design, fabrication, and measurement of a simple coplanar waveguide (CPW) type of phase shifter as well as a more complicated “hybrid” phase shifter consisting of a ferrite (YIG) in addition to BST. The use of such a bilayer allows one to “tune” the impedance of the phase shifters independently of the phase velocity through careful selection of the DC biasing magnetic fields, or alternatively through the use of an additional piezoelectric layer, bonded to YIG whose permeability can then be tuned through magnetostriction.

Master of Science / Department of Electrical and Computer Engineering / William B. Kuhn / A technique for measuring and characterizing transistor noise is presented. The primary goal of the measurements is to locate the 1/f noise corner for select transistors in Silicon-on-Sapphire processes. Additionally, the magnitude of the background channel noise of each transistor is measured. With this data, integrated circuit (IC) engineers will have a qualitative and quantitative resource for selecting transistors in designs with low noise requirements. During tests, transistor noise behavioral change is investigated over varying channel lengths, device type (N-type and P-type), threshold voltage, and bias voltage levels. Noise improvements for increased channel lengths from minimal, 1.0μm, and 4.0μm are measured. Transistors with medium and high threshold voltages are tested for comparison of their noise performance. The bias voltages are chosen to represent typical design values used in practice, with approximately 400 mV overdrive and a drain-to-source voltage range of 0.5 to 3.0V. The transistors subjected to tests are custom designed in Peregrine’s 0.5μm (FC) and 0.25μm (GC) Silicon-on-Sapphire (SOS) processes. In order to allow channel current noise to dominate over other circuit noise, the transistors have extraordinarily large aspect ratios (~2500 - 5000). The transistor noise produced is amplified and measured over a frequency range of 1kHz - 100MHz. This range allows the measurement of each device’s low and high frequency noise spectrum and resulting noise corner.

Depuis que les dimensions des nano-dispositifs ont atteint l’échelle nanométrique, la simulation quantique est devenue incontournable dans le domaine de la nanoélectronique. Parmi les différents phénomènes physiques, l’interaction électron-phonon représente un processus majeur limitant la mobilité des porteurs de charge à température ambiante. En combinant la théorie multibandes k.p avec le formalisme quantique des fonctions de Green hors-équilibre, nous avons étudié et comparé deux types de dispositifs double-grille dopés p: le transistor MOS «conventionnel» et celui dit «sans jonction». L’influence de l’orientation cristalline, du matériau semi-conducteur, de la longueur de grille et de l’épaisseur du substrat a été étudiée afin d’optimiser les performances de ces dispositifs aux dimensions ultimes. D’un point de vue plus fondamental, l’interaction avec les phonons est habituellement implémentée à partir de l’approche auto-cohérente de Born (SCBA). Nous avons exploré la validité des approches non auto-cohérentes numériquement moins coûteuse qui conservent le courant : Lowest Order Approximation (LOA). Une comparaison entre SCBA, LOA et son prolongement analytique (LOA+AC) en modèle multi-bande a été menée. / Device simulation has attracted large interest since the dimensions of electronic devices reached the nanoscale. Among the new physical phenomena observed we focus on interaction-induced effects. Particular emphasis is placed on electron-phonon interactions as it is one of the most important carrier mobility-limiting mechanisms in nanodevices. Using the k.p multiband theory combined with the Non-Equilibrium Green's Function formalism, we model 2 types of double-gate devices: p-type MOSFETs and junctionless p-type MOSFETs. The 2D architecture of the double-gate device enables us to investigate the influence of confinement in one direction, infinite propagation in the other direction and connection to semi-infinite reservoirs in the last one. Different crystallographic orientation, channel materials, gate lengths and channel widths are investigated. From a fundamental point of view, phonon scattering is usually implement via the so-called Self-Consistent Born Approximation (SCBA°. We explore the validity of a one shot current conserving method based on the Lowest Order Approximation (LOA). A comparison between SCBA, LOA and its analytic continuation (LOA+AC) in multiband models is discussed.

Insulated Gate Bipolar Transistors (IGBTs) are popular power electronic switching devices with several advantages. However, they have been known to fail in the field when subjected to significant variations in power dissipation – known as power cycling. In the work presented here, a novel alternating-current (AC) power cycling test method for IGBTs together with their free-wheeling diodes is proposed and verified. A review of previous work revealed that the parameter that most affects IGBT lifetime under power cycling conditions is the variation in its junction-case temperature difference. Through simulation, the behaviour of a conventional single phase inverter (H-bridge) using simple pulse width modulation (PWM) control was quantified, and the effect of switching frequency and load power factor was studied. Results of the simulations and literature review were used to develop design criteria for a new AC test circuit. The new AC test circuit (a modified version of the conventional H-bridge) was then designed and its performance compared to the criteria and to the simulation results of the conventional circuit. The circuit was then built and its performance was validated. The circuit complied with the performance criteria, in particular the desired variation in 7jc, to an adequate degree of accuracy. The proposed test circuit is novel for several reasons. The stresses on devices used in a conventional H-bridge using a high power factor inductive load are reproduced using a low power factor inductive load, considerably reducing the energy cost of running such a test. IGBT switching losses are not actively reduced, as is normal practice, but instead are actively increased to generate the required losses. Free-wheeling diodes are also tested, but do not have significant switching losses, as the nature of the test circuit dictates that these be transferred to the IGBTs. The main drawback of the proposed test circuit is that a larger number of devices are needed; however, this tradeoff is necessary to obtain the energy cost savings provided by this circuit.

Le développement de nouveaux matériaux pour augmenter les performances des capteurs biologiques est très important lorsqu'on sait que les signaux électriques constituent la base des évènements biologiques fondamentaux comme l’activité cérébrale, le battement du coeur ou la sécrétion hormonale. Ces signaux cellulaires sont souvent enregistrés avec des sondes qui nécessitent des modifications génétiques ou chimiques. Cependant, des signaux intrinsèques pourraient être exploités directement. Des matrices de microélectrodes extracellulaires (MEAs) et des transistors électrochimiques à base de polymères (OECTs) sont par exemple sensibles aux flux ioniques. Ils sont, de plus, non-invasifs et donnent des informations importantes sur l’activité cellulaire. Cependant, ils ne peuvent différencier les espèces ioniques impliquées dans les signaux pour l’obtention d’une image précise de l’activité électrique. Ce travail de thèse a ainsi consisté dans : le développement de polymères bivalents ion-sensibles et conducteurs électroniques, la démonstration de leur biocompatibilité avec des cellules bêta-pancréatiques, la fabrication de transistors OECTs intégrant ces matériaux et la preuve de concept de son applicabilité comme plateforme non-invasive pour la détection de flux ioniques. / The generation of novel materials to harness the power of biological sensors is extremely attractive because precisely configured electrical activities form the base of key biological events such as brain activity, heart beat or vital hormone secretion. Cellular signals are often recorded using probes that require genetic or chemical manipulation. Intrinsic signals offer the huge advantage to harness these properties without further transformations. Extracellular microelectrode arrays (MEAs) and polymer-based organic electrochemical transistor arrays (OECTs) rely on the movement of ions, are non-invasive and provide some information on cell activity. However, they cannot resolve fluxes of specific species as targeted ions to obtain a precise picture of cell/organ activity. In this context, this work has consisted on the development of multimodal ion-sensing polymers, demonstration of their biocompatibility to beta-cells, the engineer of original OECTs incorporating these materials and demonstration of their viability as non-invasive platform of electrical cell activity and specific ion fluxes.

Neste trabalho foi implementado um amplificadorpara pequenos sinais e ambiente de 50 com largaura de faixa de 500 KHz a 1,5 GHz (11,5 oitavas) , baseando se em técnicas de circuitos discretos. Utilizando 2 MESFET';s de GaAs, redes de polarizaçãoindutivas e reais de casamento sem perdas o amplificador construído apresentou um gano médio se 27,5 dB com `ripple';de 1,5 dB e uma figura de ruídomenor que 2 dB para freqüência acima de 500 MHz e menor que 3 dBpara freqüências acima de 50 MHz. Os resultados experimentais obtidos demonstram a validade de procedimento utilizado para o projeto sendo conseguido um excelente desempenho em termos de ganho, largura de faixa e figura de ruído.