Thesis (Ph. D.)--Auburn University. / Abstract. Vita. Includes bibliographical references (p. 103-114).

Dissertation (Ph.D.)--Auburn University, / Abstract. Vita. Includes bibliographic references (p.117-130).

The development of monolithic microwave integrated circuits (MMICs) has enabled the expansion of multiple circuit elements on a single piece of semiconductor, enclosed in a package with connecting leads. Attributable to the widespread use of wireless circuits and sub-systems, MMICs meet stringent demands for smaller chip area, low loss and low cost. These require highly integrated MMICs with compact features. This thesis provides valuable insight into the design of compact multifunctional MMICs using three-dimensional (3-D) multilayer technology. The proposed technology offers compact, hence low-cost solutions, where all active and passive components are fabricated vertically on the same substrate and no expensive via hole or backside processing is required. The substrate used in this work contains pre-fabricated 0.5 µm pseudomorphic High Electron Mobility Transistor (pHEMT) GaAs active devices. The performances of the uncommitted and committed pHEMTs are compared in terms of their DC, small-signal and large-signal RF measurements and modelling results. Committed pHEMT refers to the pHEMT that is connected to multilayer circuit, whereas uncommitted pHEMT is not. The effect of integrating committed pHEMTs with multilayer passive components is studied and the suitability of the multilayer fabrication processing is assessed. Using this technology, two pHEMT Schottky diodes with 120 µm and 200 µm gate widths are designed, fabricated and extensively characterised by I-V, C-V and S-parameter measurements. The information gained from the measurements is then used to extract all unknown equivalent circuit model parameters using high-frequency on-wafer microwave probing. The measured results showed good agreement with the modelled ones over the frequency range up to 40 GHz. Preliminary demonstrations of the use of these pHEMT Schottky diodes in microwave limiter and detector circuit applications are also discussed, showing promising results. Finally, the implementation of 3-D multilayer technology is shown for the first time in single-pole single-throw (SPST) and single-pole double-throw (SPDT) switches design by utilising the pre-fabricated pHEMTs. The design and analysis of the switches are demonstrated first through simulation using TriQuint's Own Model - Level 3 (TOM3). Three optimised SPST and SPDT pHEMT switching circuits which can address applications ranging from L to X bands are successfully fabricated and tested. The performance of the pHEMT switches is comparable to those of the current state-of-the-art, while simultaneously offering compact circuits with the advantages of integration with other MMIC components. All works reported in this thesis should facilitate foundry design engineers towards further development of 3-D multilayer technology.

This thesis presents a multi-stage rectifier for wireless power transfer in biomedical implant systems. The rectifier is built using Schottky diodes. The design has been simulated in 0.5µm and 130nm CMOS processes. The challenges for a rectifier in a wireless power transfer systems are observed to be the efficiency, output voltage yield, operating frequency range and the minimum input voltage the rectifier can convert. The rectifier outperformed the contemporary works in the mentioned criteria.

Submitted by Lucas Vinicius de Lima Citolino null (citolinolucas@gmail.com) on 2017-09-11T19:48:09Z No. of bitstreams: 1 Dissertacao_defesa_Citolinofinal.pdf: 3971068 bytes, checksum: 1fa455e43ce15f41cd5a185e3911cb10 (MD5) / Approved for entry into archive by Monique Sasaki (sayumi_sasaki@hotmail.com) on 2017-09-11T20:31:00Z (GMT) No. of bitstreams: 1 citolino_lvl_me_prud.pdf: 3971068 bytes, checksum: 1fa455e43ce15f41cd5a185e3911cb10 (MD5) / Made available in DSpace on 2017-09-11T20:31:00Z (GMT). No. of bitstreams: 1 citolino_lvl_me_prud.pdf: 3971068 bytes, checksum: 1fa455e43ce15f41cd5a185e3911cb10 (MD5) Previous issue date: 2017-07-21 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / O diodo Schottky orgânico permite o estudo da camada ativa e de efeitos de interfaces dos contatos elétricos, além da aplicação em estudos mais avançados, como por exemplo, em células solares, transistores e diodos orgânicos emissores de luz (OLEDs). Nestes dispositivos, dentre os parâmetros chave no funcionamento dos dispositivos destaca-se os tipos de eletrodos, a morfologia e a organização da camada ativa no estado sólido. Os politiofenos por apresentarem fácil processabilidade e notáveis propriedades do estado sólido, como aumento de condutividade elétrica, possuem grande utilização como camada ativa na forma de filmes finos. Assim a técnica de Langmuir-Schaefer (LS) se destaca, pois proporciona maior organização a nível molecular e controle na espessura e uniformidade nos filmes finos de politiofeno. Dentro deste contexto, o objetivo deste trabalho foi fabricar filmes LS de poli(3-hexiltiofeno) (P3HT) acrescido com ácido esteárico (SA), visando uma aplicação como camada ativa em diodos Schottky orgânicos para um estudo tanto das propriedades elétricas da camada ativa quanto das diferentes interfaces através das caracterizações elétricas. Para fabricação dos filmes finos e estudos das isotermas de pressão superficial (π-A) foi utilizada uma cuba de Langmuir KSV 5000. Os eletrodos inferiores (ITO, alumínio e ouro) e superiores (alumínio e ouro) foram obtidos por evaporação térmica a vácuo. As medidas de absorção, crescimento dos filmes e morfologia foram realizadas através da espectroscopia de absorção óptica UV-visível e microscopia de força atômica, respectivamente. As caracterizações elétricas foram realizadas através de medidas de corrente continua (dc) utilizando uma fonte Keithley modelo 238 e as medidas de corrente alternada (ac) foram realizadas através do analisador de impedâncias Solartron 1260A. As isotermas π-A mostraram um forte indício de que o polímero se localiza em cima de uma camada de filme de SA na interface ar-água, tornando o filme fino mais flexível. As propriedades de absorção mostraram que o SA favorece a formação de filmes finos mais organizados e com crescimento linear na deposição nos substratos. Nas medidas dc, os diodos Schottky com camadas ativas sendo os filmes de P3HT-SA apresentaram maior valores de corrente elétrica, devido o SA melhorar a organização dos filmes, assim favorecendo o transporte de portadores de carga pela camada ativa. Através das medidas ac, conclui-se que o SA além de melhorar a organização dos filmes finos, também melhora a interface entre o filme de P3HT-SA e o Al, favorecendo assim a injeção de elétrons do Al no P3HT. / The organic Schottky diode allows the study of the active layer and effects at interfaces of electric contacts, besides the application in advanced studies, such as solar cells, transistors and organic light emitting diodes (OLEDs). In these devices, among the key parameters of the operation of the devices, stand out the electrode types, the morphology and the active layer organization in the solid state. The polythiophenes have wide use as active layer of organic devices in the form of thin films because of their easy processability and remarkable properties in solid state, such as increased electrical conductivity. The Langmuir-Schaefer (LS) technique is highlighted because it provides molecular organization and control in the thickness and uniformity in the fabrication of polythiophene thin films. In this context, the aim of this work was to fabricate LS films of poly (3-hexylthiophene) (P3HT) mixed with stearic acid (SA), to apply as an active layer in organic Schottky diodes in order to study the electrical properties of active layers and different interfaces through electrical characterization. A Langmuir trough KSV 5000 was used to fabricate the thin films (active layers) and to realize studies of pressure isotherms (π-A). By physical vapor deposition the bottom electrodes (ITO, aluminum and gold) and top electrodes (aluminum and gold) were obtained. Measurements of absorption, growth and morphology of thin films were performed using Ultraviolet-visible spectroscopy and atomic force microscopy, respectively. Electrical characterizations were carried out using direct current (dc) measurements employing a Keithley 238 and the alternating current (ac) measurements were performed employing a Solartron 1260A impedance analyzer. The π-A isotherms showed a strong indication that the polymer is located above the SA layer at air-water interface, making the thin film more flexible. The absorption properties showed that the SA favors the formation of thin films more organized and with linear growth in the deposition onto substrates. In the dc measurements, the Schottky diodes with active layers being the P3HT-SA films presented higher values of current, due to the SA to improve the organization in the thin films, thus favoring the transport of charge carriers inside of active layer. Through ac measurements, it is concluded that the SA besides improving the organization of thin films, also improves the interface between P3HT-SA film and Al, thus favoring the injection of electrons in P3HT by Al electrode.

No description available.

Actuellement, dans les plateformes aérospatiales, le nombre et le besoin d’intégration des équipements électriques et électroniques sont grandissant du fait que leurs fonctions nécessitent de plus en plus de puissance. L’objectif de minimisation des coûts et surtout la disponibilité des dispositifs électroniques forcent les concepteurs et les fabricants de ces plateformes à s’orienter vers des produits commerciaux (dits grand public). La fiabilité des boîtiers des composants de puissance doit être évaluée dans les environnements sévères des applications aérospatiales. Une dizaine de composants électroniques de puissance a été sélectionnée en fonction de leur disponibilité et l’adéquation de leurs performances électriques et thermiques aux exigences des applications aérospatiales. Ces composants intègrent différents types de semi-conducteurs tels que le silicium, le carbure de silicium et le nitrure de gallium. Tout d’abord, une étude a été menée sur les potentiels modes et mécanismes de défaillance de ces composants électroniques de puissance dans ces environnements. Elle a permis de mettre en place plusieurs procédures de vieillissement accéléré ainsi que le développement de deux bancs de tests pour suivre électriquement le vieillissement de ces composants. Ces tests ont été menés sur deux diodes Schottky SiC, commercialisées par deux fabricants, regroupant les technologies des boîtiers des composants électroniques de puissance. Les analyses de défaillance ont tout d’abord mis en évidence une immaturité de la technologie de la jonction Schottky des puces SiC de l’une des deux diodes soumis à une tension inverse. Ces défaillances sont attribuées à la destruction partielle de la structure Schottky et indique une reproductibilité non maitrisée de la fabrication des puces de ce composant. Ensuite, ces analyses ont mis en évidence plusieurs mécanismes de vieillissement lors de tests simulant des régimes « On-Off » des applications (cycles thermiques de puissance). Celui considéré comme la cause de la défaillance est la fissuration de la soudure des fils d’interconnexion avec la puce. Une loi pouvant décrire la fissuration des interconnexions a été identifiée à la suite des évolutions des cycles thermiques de puissance à l’approche de la défaillance. L’étude de ces évolutions a permis de démarrer l’élaboration d’un modèle physique de défaillance adapté aux interconnexions de la puce en vue d’estimer la durée de vie des composants commerciaux. / Currently, in the aerospace platforms, the number and the need for integration of the electric and electronic equipment are growing because their functions require more and more power. The goal of cost minimization and mostly the availability of power electronic devices push the designers and the manufacturers of these platforms moving towards commercial products (Component Off-The Shelf). The packaging reliability of power electronic components must be assessed in harsh environments of aerospace applications. A dozen of power electronic components have been selected in accordance with their availability and with the adequacy of their electrical and thermal performances according to the requirements of aerospace applications. These components integrate different types of semi-conductors such as silicon, silicon carbide and gallium nitride. Foremost, a study has been leaded on the potential failure modes and mechanisms of these power electronic components in these environments. It has permitted to put in place several procedures of accelerated ageing and the development of two test benches to electrically monitor the ageing of these components. These tests have been carried on two SiC Schottky diodes, marketed by two manufacturers, gathering the technologies of the packaging of power electronic components. The failure analyses have first highlighted an immaturity of the Schottky junction technology of the SiC die of one of the two diodes subjected to a reverse voltage. These failures are attributed to the partial destruction of the Schottky structure and indicate a not mastered reproducibility of the die manufacturing of these components. Then, these analyses have highlighted several ageing mechanisms during tests simulating « On-Off » power of applications (power thermal cycles). One considered as the failure cause is the cracking of the welding of the wire bonding with the die. A behavioral law that can describe the cracking of the interconnections has been identified according to the evolutions of the power thermal cycles when near to failure. The study of these evolutions have permitted to start the elaboration of a physical model of failure adapted to the die interconnections in order to estimate the lifetime of commercial components.

Les composants électroniques utilisés pour des applications spatiales sont soumis à des rayonnements susceptibles de les rendre inopérants. Pour se prémunir de tels effets, leur sensibilité est testée au sol dans des accélérateurs de particules, onéreux et complexes à mettre en œuvre. Ce travail de thèse porte sur l’utilisation d’impulsions laser pour reproduire sous certaines conditions les effets des ions lourds. Le déclenchement de phénomènes parfois destructifs sur plusieurs types de composants de niveaux d’intégration différents a été obtenu sur le banc laser développé pendant cette thèse. Cela ouvre la voix à l’utilisation du laser comme outil de diagnostic en tirant partie de ses avantages en termes d’accessibilité, de coûts et de compréhension fine des effets. / Electronic components used for space applications may exhibit failures under radiation. To prevent uch effects, the radiation sensitivity is evaluated using particle accelerators. Since those facilities are nly few around the world and expensive, complementary tests are needed to analyse radiation ensitivity. This work contributes to the use of laser pulses to reproduce under given conditions the ffects of heavy ions. Using the laser set-up developed during this thesis, single events which may be estructive were triggered on several types of electronic components. This paves the way to the use of aser as a diagnostic tool, given its advantages in terms of accessibility, costs and detailed analysis

Through the history of mankind, novel materials have played a key role in techno- logical progress. As we approach the limits of scaling it becomes difficult to squeeze out any more extensions to Moore’s law by just reducing device feature sizes. It is important to look for an alternate semiconductor to silicon in order to continue making the progress predicted by Moore’s law. Among the various semiconductor options being explored world-wide, the III-nitride semiconductor material system has certain unique characteristics that make it one of the leading contenders. We explore the III-nitride semiconductor material system for the unique advantages that it offers over the other alternatives available to us. This thesis studies the device applications of epitaxial III-nitride films and nanos- tructures grown using plasma assisted molecular beam epitaxy (PAMBE) The material characterisation of the PAMBE grown epitaxial III-nitrides was car- ried out using techniques like high resolution X-ray diffraction (HR-XRD), field emis- sion scanning electron microscopy (FESEM), room temperature photoluminescence (PL) and transmission electron microscopy (TEM). The epitaxial III-nitrides were then further processed to fabricate devices like Schottky diodes, photodetectors and surface acoustic wave (SAW) devices. The electrical charcterisation of the fabricated devices was carried out using techniques like Hall measurement, IV and CV measure- ments on a DC probe station and S-parameter measurements on a vector network analyser connected to an RF probe station. We begin our work on Schottky diodes by explaining the motivation for adding an interfacial layer in a metal-semiconductor Schottky contact and how high-k di- electrics like HfO2 have been relatively unexplored in this application. We report the work carried out on the Pt/n-GaN metal-semiconductor (MS) Schottky and the Pt/HfO2/n-GaN metal-insulator-semiconductor (MIS) Schottky diode. We report an improvement in the diode parameters like barrier height (0.52 eV to 0.63 eV), ideality factor (2.1 to 1.3) and rectification ratio (35.9 to 98.9 @2V bias) after the introduction of 5 nm of HfO2 as the interfacial layer. Temperature dependent I-V measurements were done to gain a further understanding of the interface. We observe that the barrier height and ideality factor exhibit a temperature dependence. This was attributed to inhomogeneities at the interface and by assuming a Gaussian distribution of barrier heights. UV and IR photodetectors using III-nitrides are then studied. Our work on UV photodetectors describes the growth of epitaxial GaN films. Au nanoparticles were fabricated on these films using thermal evaporation and annealing. Al nanostruc- tures were fabricated using nanosphere lithography. Plasmonic enhancement using these metallic nanostructures was explored by fabricating metal-semiconductor-metal (MSM) photodetectors. We observed plasmonic enhancement of photocurrent in both cases. To obtain greater improvement, we etched down on the GaN film using reac tive ion etching (RIE). This resulted in further increase in photocurrent along with a reduction in dark current which was attributed to creation of new trap states. IR photodetectors studied in this thesis are InN quantum dots whose density can be controlled by varying the indium flux during growth. We observe that increase in InN quantum dot density results in increase in photocurrent and decrease in dark current in the fabricated IR photodetectors. We then explore the advantages that InGaN offers as a material that supports surface acoustic waves and fabricate InGaN based surface acoustic wave devices. We describe the growth of epitaxial In0.23 Ga0.77 N films on GaN template using molecular beam epitaxy. Material characterisation was carried out using HR-XRD, FESEM, PL and TEM. The composition was determined from HR-XRD and PL measurements and both results matched each other. This was followed by the fabrication of interdigited electrodes with finger spacing of 10 µm. S-parameter results showed a transmission peak at 104 MHz with an insertion loss of 19 dB. To the best of our knowledge, this is the first demonstration of an InGaN based SAW device. In summary, this thesis demonstrates the practical advantages of epitaxially grown film and nanostructured III-nitride materials such as GaN, InN and InGaN using plasma assisted molecular beam epitaxy for Schottky diodes, UV and IR photodetec- tors and surface acoustic wave devices.

Group III-nitride semiconductors have received much research attention and witnessed a significant development due to their ample applications in solid-state lighting and high-power/high-frequency electronics. Numerous growth methods were explored to achieve device quality epitaxial III-nitride semiconductors. Among the growth methods for III-nitride semiconductors, molecular beam epitaxy provides advantages such as formation of abrupt interfaces and in-situ monitoring of growth. The present research work focuses on the growth and characterizations of III-nitride based epitaxial films, nanostructures and heterostructures on c-sapphire substrate using plasma-assisted molecular beam epitaxy system. The correlation between structural, optical and electrical properties of III-nitride semiconductors would be extremely useful. The interfaces of the metal/semiconductor and semiconductor heterostructures are very important in the performance of semiconductor devices. In this regard, the electrical transport studies of metal/semiconductor and semiconductor heterostructures have been carried out. Besides, studies involved with the defect induced room temperature ferromagnetism of GaN films and InN nano-structures have also been carried out. The thesis is organized in eight different chapters and a brief overview of each chapter is given below. Chapter 1 provides a brief introduction on physical properties of group III-nitride semiconductors. It also describes the importance of III-nitride heterostructures in the operation of optoelectronic devices. In addition, it also includes the current strategy of the emergence of room temperature ferromagnetism in III-nitride semiconductors. Chapter 2 deals with the basic working principles of molecular beam epitaxy system and different characterization tools employed in the present work. Chapter 3 describes the growth of GaN films on c-sapphire by plasma-assisted molecular beam epitaxy. The effects of N/Ga flux ratio on structural, morphological and optical properties have been studied. The flux ratio plays a major role in controlling crystal quality, morphology and emission properties of GaN films. The dislocation density is found to increase with increase in N/Ga flux ratio. The surface morphologies of the films as seen by scanning electron microscopy show pits on the surface and found that the pit density on the surface increases with flux ratio. The room temperature photoluminescence study reveals the shift in band-edge emission towards the lower energy with increase in N/Ga flux ratio. This is believed to arise from the reduction in compressive stress in the GaN films as it is evidenced by room temperature Raman study. The transport studies on the Pt/GaN Schottky diodes showed a significant increase in leakage current with an increase in N/Ga ratio and is found to be caused by the increase in dislocation density in the GaN films. Chapter 4 deals with the fabrication and characterization of Au/GaN Schottky diodes. The temperature dependent current–voltage measurements have been used to determine the current transport mechanism in Schottky diodes. The barrier height (φb) and the ideality factor (η) are estimated from the thermionic emission model and are found to be temperature dependent in nature, indicating the existence of barrier height inhomogeneities at the Au/GaN interface. The conventional Richardson plot of ln(Is/T2) versus 1/kT gives Richardson constant value of 3.23×10-5 Acm-2 K-2, which is much lower than the known value of 26.4 Acm-2 K-2 for GaN. Such discrepancy of Richardson constant value was attributed to the existence of barrier height inhomogeneities at the Au/GaN interface. The modified Richardson plot of ln(Is/T2)-q2σs2/2k2T2 versus q/kT, by assuming a Gaussian distribution of barrier heights at the Au/GaN interface, provides the Schottky barrier height of 1.47 eV and Richardson constant value of 38.8 Acm-2 K-2 which is very close to the theatrical value of Richardson constant. The temperature dependence of barrier height is interpreted on the basis of existence of the Gaussian distribution of the barrier heights due to the barrier height inhomogeneities at the Au/GaN interface. Chapter 5 addresses on the influence of GaN underlayer thickness on structural, electrical and optical properties of InN thin films grown using plasma-assisted molecular beam epitaxy. The high resolution X-ray diffraction study reveals superior crystalline quality for the InN film grown on thicker GaN film. The electronic and optical properties seem to be greatly influenced by the structural quality of the films, as can be evidenced from Hall measurement and optical absorption spectroscopy. Also, we present the studies involving the dependence of structural, electrical and optical properties of InN films, grown on thicker GaN films, on growth temperature. The optical absorption edge of InN film is found to be strongly dependent on carrier concentration. Kane’s k.p model is used to describe the dependence of optical absorption edge on carrier concentration by considering the non-parabolic dispersion relation for carrier in the conduction band. Chapter 6 deals with the analysis of the temperature dependent current transport mechanisms in InN/GaN heterostructure based Schottky junctions. The barrier height (φb) and the ideality factor (η) of the InN/GaN Schottky junctions are found to be temperature dependent. The temperature dependence of the barrier height indicates that the Schottky barrier height is inhomogeneous in nature at the heterostructure interface. The higher value of the ideality factor and its temperature dependence suggest that the current transport is primarily dominated by thermionic field emission (TFE) other than thermionic emission (TE). The room temperature barrier height and the ideality factor obtained by TFE model are 1.43 eV and 1.21, respectively. Chapter 7 focuses on the defect induced room temperature ferromagnetism in Ga deficient GaN epitaxial films and InN nano-structures grown on c-sapphire substrate by using plasma-assisted molecular beam epitaxy. The observed yellow emission peak in room temperature photoluminescence spectra and the peak positioning at 300 cm-1 in Raman spectra confirms the existence of Ga vacancies in GaN films. The ferromagnetism in Ga deficient GaN films is believed to originate from the polarization of the unpaired 2p electrons of nitrogen surrounding the Ga vacancy. The InN nano-structures of different size are grown on sapphire substrate, the structural and magnetic properties are studied. The room temperature magnetization measurement of InN nano-structures exhibits the ferromagnetic behavior. The saturation magnetization is found to be strongly dependent on the size of the nano-structures. Finally, Chapter 8 gives the summary of the present work and the scope for future work in this area of research.