<p>Gallium Nitride based devices due to their inherent material properties are considered as one of the most promising devices to realize high power, high frequency transistors with lower power consumption in next-generation applications. Although the technology has been studied since early 1970s, there is still a vast room and expectations in its yet unachieved findings. In present work the GaN technology is explored and state-of-the-art studies of GaN based HEMTs and their application in MMICs are presented. Different designs are presented and evaluated and the results are reported. In particular the HEMT performance is studied in terms of DC in addition to large signal conditions, where the device’s performance becomes function of power levels it is driven with. The peculiarities and challenges of building an automated Load-Pull setup are outlined and analysis for further improvements is presented.</p>

Gallium Nitride based devices due to their inherent material properties are considered as one of the most promising devices to realize high power, high frequency transistors with lower power consumption in next-generation applications. Although the technology has been studied since early 1970s, there is still a vast room and expectations in its yet unachieved findings. In present work the GaN technology is explored and state-of-the-art studies of GaN based HEMTs and their application in MMICs are presented. Different designs are presented and evaluated and the results are reported. In particular the HEMT performance is studied in terms of DC in addition to large signal conditions, where the device’s performance becomes function of power levels it is driven with. The peculiarities and challenges of building an automated Load-Pull setup are outlined and analysis for further improvements is presented.

No description available.

Le Nitrure de Gallium est devenu un matériau incontournable pour le développement de dispositifs semi-conducteurs aux performances très supérieures aux composants silicium. L'immense potentiel du dispositif HEMT AlGaN / GaN provient du gaz d'électrons à haute densité et à forte mobilité formé au niveau de son hétéro-structure. Cependant, le fonctionnement sous champ électrique, température et conditions de stress élevés rend le dispositif vulnérable aux problèmes de fiabilité qui limitent son efficacité et sa durée de vie. Les pièges présents dans la structure, qui limitent la densité porteurs du canal et pénalisent la réponse du dispositif, constituent le facteur majeur déterminant plusieurs effets électriques parasites et la fiabilité du dispositif. L’industrie du GaN est confrontée à la nécessité de disposer de dispositifs de haute fiabilité si bien qu’il est nécessaire de faire des progrès dans l’analyse de l’impact des pièges pour en déduire des solutions technologiques permettant leur inhibition.La motivation de ce travail est d’identifier les signatures électriques associées à l’activité de différents pièges ainsi que leurs conséquences sur les performances et la fiabilité des HEMT GaN grâce à une étude dédiée des dispositifs de la technologie GH-25 conçue pour des applications RF de puissance fonctionnant jusqu’à 20 GHz. L’étude utilise des simulations physiques TCAD. Une analyse détaillée des effets indépendants et interdépendants est réalisée afin d'identifier l'impact relatif des pièges pour des études de cas où les caractéristiques électriques présentent des écarts importants par rapport à la réponse idéale du dispositif.La méthodologie utilisée pour développer un modèle TCAD représentatif et dérivé de la physique interne est décrite en accordant une attention particulière au courant de fuite de grille qui reflète l'influence de processus physiques fondamentaux ainsi que les effets parasites couramment rencontrés dans les dispositifs GaN. Les simulations ciblées établissent un lien entre l'observation d'un problème de fiabilité et son origine sous-jacente dans les phénomènes de piégeage.L’établissement d’associations entre la localisation spatiale des pièges et les dégradations qu’ils pourraient provoquer est un objectif important de cette thèse.Plusieurs stratégies de simulation sont présentées, permettant d’explorer le comportement des pièges en régime permanent et en régime transitoire et donnant une perception détaillée de la manière dont les paramètres des pièges affectent les caractéristiques opérationnelles. Des approches pour distinguer les interactions de pièges différents sont également décrites. L’étude centrale de cette thèse est un phénomène de courant de fuite parasite complexe, identifié dans le procédé GH 25comme conséquence du vieillissement accéléré. Connu sous le nom de «belly-shape», il représente un exemple intéressant de la façon dont les stratégies développées peuvent être appliquées pour discerner la causalité, l'impact et l'évolution des pièges responsables du phénomène. Afin d'approfondir l'analyse des modes de piégeage, nous avons procédé à des tests de vieillissement accéléré et des caractérisations électro-optiques afin de modifier la dynamique générale du mécanisme de piégeage et d'observer la modulation du mécanisme du piégeage sur la réponse du dispositif. / Gallium Nitride has emerged as a terrific contender to lead the future of the semiconductor industry beyond the performance limits of silicon.The immense potential of the AlGaN/GaN HEMT device is derived from the high density, high mobility electron gas formed at its hetero-structure. However, frequent subjection to high electric field, temperature and stress conditions makes the device vulnerable to reliability issues that restrict its efficiency and life time. A dominant contributor to several parasitic and reliability issues are traps present within the semiconductor structure which restrict the channel density and aggravate the device static and dynamic response. As the GaN industry addresses an increasing demand for superior devices, reliability analysis is of critical importance. There is a necessity to enable advancements in trap inhibition which would allow the realization of stronger, efficient devices.The motivation of this work is to recognize distinct ways in which various traps affect the performance and reliability metrics of GaN 0.25 µm HEMTs through a study of devices of the GH-25 process optimized for high power applications up to 20 GHz. The investigation employs physical TCAD simulations to provide insight and perspective to electrical and optical characterizations. Detailed analysis into independent and interrelated effects is performed to identify the relative impact of traps in circumstances presenting notable deviations from the ideal device response.The methodology to develop a representative TCAD model derived closely from internal physics is described with special focus on the sensitive gate leakage characteristic which reflects the influence of fundamental physical processes as well as parasitic effects commonly encountered in GaN HEMTs. Targeted simulations provide a pivotal link between the observation of a reliability issue and its underlying origin in trapping phenomena. Establishing associations between the spatial location of traps and the degradations they could trigger is an important objective of this thesis.Several simulation strategies that explore trapping behavior in various steady state and transient environments are discussed which allow detailed perception into the manner and extent to which trap attributes affect operational considerations. Approaches to distinguish disparate trap interactions are also described. The central case study in this thesis is an abstruse parasitic leakage phenomenon, identified in the GH 25 process as a consequence of aging stress. Referred to as the “belly shape”, it presents an interesting example of how the developed strategies can be applied to discern the causality, impact and evolution of the responsible traps. In order to take a deeper look into trapping modes, further aging and LASER characterizations are performed to alter the general occupational dynamics and observe the modulation of trap control over device response.

Cette thèse s’inscrit dans le domaine de l’amplification de puissance microonde linéaire et haut rendement en technologie GaN. Le premier chapitre décrit le contexte général de l’émission de signaux microondes de puissance pour les télécommunications sans fil, avec un focus particulier apporté sur l’amplificateur de puissance RF. Les différents critères de linéarité et d’efficacité énergétique sont introduits.Le second chapitre présente plus particulièrement la technologie GaN et le transistor de puissance comme brique de base pour l’amplification de puissance microonde. Une revue synthétique des différentes architectures relevées dans la littérature relative à l’amplification à haut rendement est faite.En troisième chapitre, le banc de mesure temporelle d’enveloppe développé et servant de support expérimental à cette étude est présenté. Les procédures d’étalonnage et de synchronisation sont décrites. En illustration, une nouvelle méthode de mesure du NPR large bande est présentée, et validée expérimentalement.Une solution d’amplification adaptative innovante est étudiée dans le quatrième chapitre, et constitue le cœur de ce mémoire. Celle-ci se base sur le contrôle dynamique de la polarisation de grille autour du point de pincement, au rythme de l’enveloppe de modulation. Un démonstrateur d’amplification 10W GaN en bande S (2.5GHz) est développé. Comparativement à la classe B fixe, une forte amélioration de la linéarité est obtenue, sans impact notable sur le rendement moyen de l’amplificateur RF. Finalement, une investigation de la technique proposée pour l’amélioration du rendement du modulateur dans l’architecture d’envelope tracking de drain est menée. / This work deals with linear and high efficiency microwave power amplification in GaN technology.The first chapter is dedicated to the general context of wireless telecommunication with a special emphasis on the RF power amplifier. The most representative figures of merit in terms of linearity and power efficiency are introduced.The second chapter deals more specifically with the GaN technology and GaN-based transistor for microwave power amplification. A description of the principal architectures found in the literature related to high efficiency and linear amplification is summarized.In the third chapter, the developed envelope time-domain test bench is presented. Time-synchronization and envelope calibration procedures are discussed. As an illustration, a new specific wideband NPR measurement is presented and experimentally validated.An innovative power amplifier architecture is presented in the fourth chapter. It is based on a specific dynamic gate biasing technique of the power amplifier biased close to the pinch-off point. A 10W GaN S-band demonstrator has been developed. Compared to fixed class-B conditions, a linearity improvement has been reported without any prohibitive efficiency degradation of the RF power amplifier. Finally, an investigation of the proposed technique for the efficiency improvement in the drain envelope tracking technique is proposed.

Gallium Nitride (GaN) is considered a very promising material for use in the field of power devices as its application in power systems would result in a significant increase in the power density, reduced power losses, and the potential to operate at high frequencies. The wide bandgap of the material allows a high critical electric field to be sustained which can lead to the design of devices with a shorter drift region, and therefore with lower on-state resistance, if compared to a silicon-based device with the same breakdown voltage. The use of an AlGaN/GaN heterostructure allows the formation of a two-dimensional electron gas (2DEG) at the heterointerface where carriers can reach very high mobility values. These properties can lead to the production of High Electron Mobility Transistors (HEMTs) and Schottky barrier diodes with superior performance, even when compared to devices based on state-of-the-art technologies such as Silicon Carbide or superjunctions. Furthermore, epitaxial growth of GaN layers on silicon wafers allows a significant reduction in the production cost and makes these devices competitive from a price perspective. This thesis will deal with a variety of topics concerning the characterization, design and optimization of AlGaN/GaN HEMTs and Schottky diodes with a 600 to 650V rating. Discussion will span several topics from device cross-section physics to circuit implementation and will be based on both experimental results and advanced modelling. More specifically, the thesis is concerned with the characterization of AlGaN/GaN Schottky diodes and extraction of their main parameters such as ideality factor, barrier height and series resistance. A thorough investigation of their reverse recovery performance and a comparison to competing technologies is also given. Several topics which concern the operation of AlGaN/GaN HEMTs are then discussed. The underlying physics of p-gate enhancement mode transistors are analysed followed by a discussion of the challenges associated with the implementation of these devices at a circuit level. Finally, a comparison of the performance of a specific area-saving layout (Bonding pad over active area) and a conventional design is given. The thesis aims to significantly enhance the understanding of the behaviour of these devices to enable better or new commercial designs to emerge.

No description available.

L’industrie des transports aéronautique et terrestre voit une augmentation constante de l’électrification de ses fonctions. Les actionneurs mécaniques ou hydrauliques sont au fil des évolutions technologiques remplacés par des actionneurs électriques.Les composants qui dominent le marché actuellement ne semblent plus capables de suivre la tendance. En effet, les composants de puissance à base de silicium règnent toujours sur le marché actuel, grâce à leur faible coût. Ce matériau commence par contre à atteindre ses limites théoriques en termes de performances. Dans ce contexte, différentes structures en semi-conducteurs à large bande interdite sont en train d’émerger afin de succéder au silicium.Cette étude a pour objectif d’évaluer la fiabilité des transistors de puissance à base de Nitrure de Gallium. Ces composants semblent être très prometteurs pour des applications moyennes puissances. Cependant, les mécanismes de défaillance dont peuvent souffrir ces composants ne sont pas encore suffisamment étudiés. L’étude consiste en l’application de vieillissements alliant contraintes thermiques et électriques. Ces vieillissements sont effectués à différentes conditions de tension et de température. L’objectif de cette méthode est, dans un premier temps, d’isoler l’effet de chaque facteur de stress sur l’état des composants, et dans un second temps, d’identifier les mécanismes de défaillances activés en fonction des conditions de vieillissement.Ce travail a permis d’identifier l’existence de différents mécanismes de défaillance pouvant être activés selon les conditions de vieillissement. En effet, il est apparu que la gamme de température de vieillissement utilisée influe grandement sur la prédominance des mécanismes de défaillance activés. Les résultats obtenus remettent en question les normes de qualification actuellement appliquées aux composants en Nitrure de Gallium. Ces normes devraient revoir à la hausse les températures de vieillissement utilisées afin de couvrir des gammes plus proches des températures d’utilisation pour ce type de composants. / The aeronautical and terrestrial transport industries know a steady increase in the electrification of their functions. In fact, the mechanical or hydraulic actuators are gradually replaced by electric ones.The components dominating the market today seem unable to follow the trend anymore. In fact, silicon-based power components still prevail in the current market, thanks to their low cost. However, this material begins to reach its theoretical limits in terms of performance. In this context, different wide bandgap semiconductor structures are emerging to take on from silicon.The aim of this study is to assess the reliability of power transistors based on Gallium Nitride. These components are very promising for medium power applications. However, the failure mechanisms of these components are not yet sufficiently studied. The study consists in the application of aging tests combining thermal and electrical stresses. These agings are carried out under different conditions of tension and temperature. The objective of this method is, firstly, to isolate the effect of each stressor on the state of the components, and secondly, to identify the failure mechanisms activated according to the aging conditions.This work made it possible to identify the existence of different failure mechanisms that can be activated according to the aging conditions. Indeed, it has emerged that the aging temperature range used influences the predominance of activated failure mechanisms. The results challenge the adequacy of current qualification standards for Gallium Nitride components. These standards should revise upwards the aging temperatures used to cover ranges closer to the operating temperatures of this kind of components.

This dissertation presents a comparative study about the performance of silicon (Si) and gallium nitride (GaN) semiconductors in drivers for light emitting diodes. Hereby, it is expected to provide the theoretical background required for the development of future works using this new technology. Theoretical aspects related to the materials used in the manufacture of semiconductors and their implications in the final product, as well as the characteristics and peculiarities of GaN semiconductors are presented. The experimental development consisted of two case studies, each focused on a distinct topology with different types of GaN semiconductors. First, a comparison of Si and enhancement mode GaN transistors was carried out in a family of synchronous buck converters. Ten 48 V to 28.3 V and 22.6 W converters were designed with the same parameters, at five different switching frequencies, ranging from 100 kHz to 1 MHz. Efficiency and temperatures were measured in four different scenarios: with and without an external diode in parallel with the low-side switch and with two different dead-time values, 25 ns and 50 ns. Converters with GaN transistors showed higher efficiency and lower temperatures in all cases, with a maximum efficiency of 96.8% and a minimum of 94.5%. In addition, Si-based converters exhibited greater performance degradation as the switching frequency and dead time increased. In the second study, nine 75 W off-line integrated double buck-boost converters were developed and evaluated. Two different Si technologies were compared with a cascode GaN transistor at three switching frequencies, ranging from 50 to 150 kHz. Again, the efficiency and temperatures of the prototypes were measured. The converters with GaN demonstrated superior performance in all cases, yielding about 5% gain in efficiency over the worst tested Si semiconductor. In both cases, the converters’ loss distribution was presented based on simulation results. It was concluded that the gallium nitride transistors have the potential to replace silicon technology mainly due to its superior performance and requirement of small, or no change, in the original circuit. / A presente dissertação apresenta um estudo comparativo do desempenho de semicondutores de silício (Si) e nitreto de gálio (GaN) em circuitos utilizados na alimentação de diodos emissores de luz. Por meio deste, procura-se fornecer o embasamento teórico necessário para o desenvolvimento de trabalhos futuros utilizando esta nova tecnologia. São apresentados, inicialmente, aspectos teóricos relacionados aos materiais utilizados na fabricação de semicondutores e suas implicações no produto final, além das características e peculiaridades dos semicondutores GaN. O desenvolvimento experimental consistiu de dois estudos de caso, cada um focado em uma topologia distinta com tipos de semicondutores GaN diferentes. Primeiramente, realizou-se um comparativo de transistores Si e GaN do tipo intensificação em uma família de conversores buck síncronos. Dez conversores 48 V para 28,3 V e 22,6 W foram projetados, com os mesmos parâmetros, em cinco diferentes frequências de comutação, variando de 100 kHz a 1 MHz. Eficiência e temperaturas foram medidas em quatro diferentes cenários: com e sem um diodo externo em paralelo com o interruptor de roda-livre e com dois valores diferentes de tempo morto, 25 ns e 50 ns. Os conversores com transistores GaN apresentaram maior eficiência e menores temperaturas em todos os casos, com uma eficiência máxima de 96,8% e uma mínima de 94,5%. Além disso, os conversores com Si exibiram uma maior degradação de desempenho à medida que a frequência de comutação e o tempo morto aumentam. No segundo estudo, nove conversores duplo buck-boost integrados de 75 W com alimentação a partir da rede elétrica foram desenvolvidos e avaliados. Compararam-se duas tecnologias distintas de interruptores de Si com um transistor GaN do tipo cascode, em três frequências de comutação, variando de 50 a 150 kHz. Novamente, mediu-se a eficiência e temperaturas dos protótipos. Os conversores com GaN demonstraram desempenho superior em todos os casos, com um ganho de cerca de 5% no rendimento em relação ao pior semicondutor Si testado. Em ambos os estudos de caso, a distribuição de perdas dos conversores foi apresentada com base em resultados de simulação. Concluiu-se que os transistores de nitreto de gálio têm potencial para substituir a tecnologia de silício utilizada atualmente devido, principalmente, a seu desempenho superior e exigência de pouca, ou nenhuma, mudança no circuito original.

abstract: The drive towards device scaling and large output power in millimeter and sub-millimeter wave power amplifiers results in a highly non-linear, out-of-equilibrium charge transport regime. Particle-based Full Band Monte Carlo device simulators allow an accurate description of this carrier dynamics at the nanoscale. This work initially compares GaN high electron mobility transistors (HEMTs) based on the established Ga-face technology and the emerging N-face technology, through a modeling approach that allows a fair comparison, indicating that the N-face devices exhibit improved performance with respect to Ga-face ones due to the natural back-barrier confinement that mitigates short-channel-effects. An investigation is then carried out on the minimum aspect ratio (i.e. gate length to gate-to-channel-distance ratio) that limits short channel effects in ultra-scaled GaN and InP HEMTs, indicating that this value in GaN devices is 15 while in InP devices is 7.5. This difference is believed to be related to the different dielectric properties of the two materials, and the corresponding different electric field distributions. The dielectric effects of the passivation layer in millimeter-wave, high-power GaN HEMTs are also investigated, finding that the effective gate length is increased by fringing capacitances, enhanced by the dielectrics in regions adjacent to the gate for layers thicker than 5 nm, strongly affecting the frequency performance of deep sub-micron devices. Lastly, efficient Full Band Monte Carlo particle-based device simulations of the large-signal performance of mm-wave transistor power amplifiers with high-Q matching networks are reported for the first time. In particular, a CellularMonte Carlo (CMC) code is self-consistently coupled with a Harmonic Balance (HB) frequency domain circuit solver. Due to the iterative nature of the HB algorithm, this simulation approach is possible only due to the computational efficiency of the CMC, which uses pre-computed scattering tables. On the other hand, HB allows the direct simulation of the steady-state behavior of circuits with long transient time. This work provides an accurate and efficient tool for the device early-stage design, which allows a computerbased performance evaluation in lieu of the extremely time-consuming and expensive iterations of prototyping and experimental large-signal characterization. / Dissertation/Thesis / Ph.D. Electrical Engineering 2011