Modélisation distribuée et évolutive du GaN HEMT

L’industrie de télécommunication et les satellites se base majoritairement sur les technologies Si et GaAs. La demande croissante des hauts débits de données entraine une facture élevée en énergie. En outre, la saturation de la bande des basses fréquences, le besoin des débits élevés et les exigences de la haute puissance imposait l’utilisation de la bande hautes fréquences. Dans le but de résoudre les problèmes cités auparavant, la technologie GaN est introduite comme un candidat prometteur qui peut offrir de la haute puissance, taille du circuit plus faible avec une meilleure stabilité mécanique aux environnements hostiles/milieux agressifs. À titre d’exemple, l‘agence spatiale européenne sont en cours de développement d’un circuit à base du GaN sur substrat en Si pour faible cout, une hautes performance et une grande fiabilité. La technologie GaN est assez mature pour proposer de nouveaux systèmes intégrés utilisés pour les puissances microonde ce qui permet une réduction considérable de la taille du système. Étant un semiconducteur à grande bande interdite, GaN peut offrir une haute puissance sous hautes températures (>225oC) avec une bonne stabilité mécanique. Elle présente un facteur de bruit faible, qui est intéressant notamment pour les circuits intégrés aux ondes millimétriques. À noter que la mobilité du GaN par rapport à la température est assez élevée pour proposer des amplificateurs dans la bande W. Avec le progrès du procédé de fabrication du GaN, notre objectif est l’introduction de cette technologie dans des applications industrielles. À cette fin, on désire avoir un modèle du dispositif qui correspond à la meilleure performance. Ensuite, on veut le valider dans une modélisation du circuit. Cette thèse, basée sur la technologie GaN unique développée au 3IT, a pour objectif l’amélioration de l’outil de conception en réduisant son erreur avec une validation de son utilisation dans la conception du circuit. Ce travail est réalisé pour la première fois au 3IT avec des résultats de simulation pour une conception idéale d’un circuit MMIC ainsi que sa démonstration. Une caractérisation des échantillons a été réalisée avec objectif d’extraction de données qui vont servir à l’alimentation de modélisation des transistors sur l’outil ADS. Une fois complétée, la modélisation a été validée par une modélisation des petits et grands signaux et a été testée par une mesure load-pull. Enfin, ce modèle a été utilisé lors de la conception d’un amplificateur pour les applications RF. L’innovation de ce travail réside dans la modélisation de la résistance d’une grille large sous forme de quadripôles parallèles à structure 3D (ou à résistances de grille distribuées) du transistor MOSHEMT GaN. La conception et la fabrication de l’amplificateur à haute puissance (HPA) aux fréquences microondes (≤4GHz) sont réalisés au LNN du 3IT et inclus une couche d’oxyde de grille afin de réduire le courant de fuite notamment pour les tensions Vgs élevées, la grille du transistor forme un serpentin pour fournir une puissance de sortie élevée avec un encombrement spatial minimal et une grille présentant une électrode de champ pour permettre d’augmenter la tension de claquage.Abstract : The telecommunication and satellite industry is mainly relying on Si and GaAs technologies as the demand for a high data rate is continuously growing, leading to higher power consumption. Moreover, the lower frequency band's saturation, the need for high data rate, and high-power force to utilize the high-frequency band. In pursuit of solving the issues mentioned earlier, GaN technology has been introduced as a promising candidate that can offer high power at a smaller circuit footprint and higher mechanical stability in harsh environments. For example, currently, the European space agency (ESA) is developing an integrated circuit with GaN on Si substrate for low cost, high performance, and high reliability. GaN technology is sufficiently mature to propose integrated new systems which are needed for microwave power range. This technology reduces the size of the system considerably. GaN is a wide bandgap semiconductor which can offer remarkably high power at high temperature (>225℃), and it is very stable mechanically. It presents a low noise factor, very interesting for a millimeter-wave integrated circuit. Finally, the mobility of GaN vs. temperature is sufficiently elevated to propose a power amplifier in W-Band. With the improvement of the GaN process, our objective is to introduce this technology for industrial applications. For this purpose, we wish to have a better model of the device that corresponds to the best performance and then validate it by using this model in a circuit. Based on the 3IT's GaN process, which is unique in its context, this thesis aims to improve the design kit by reducing the design model's error and validating it by using it in circuit design. This work is the first to realize in 3IT with simulation results to design an MMIC circuit for demonstration. I first characterized the new samples by performing different measurements than using these measurement data; transistor is modeled in ADS software. Once the model was completed, it is validated by small-signal modeling, and then the large-signal model is tested with non-linear capacitances, current source, and transconductance modeling. Finally, we used this model to design a power amplifier for RF application. The innovation comes from modeling large gate resistance as distributed gate resistance for GaN MOSHEMT transistor and then designing high-power amplifier (HPA) in the frequency range (≤ 4GHz) while using 3IT GaN process which includes first oxide layer to have low gate current and more voltage of Vgs, the second transistor is meander to have high power and third, field plate - gate for high breakdown voltage

AlN/GaN MOS-HEMTs technology

The ever increasing demand for higher power devices at higher frequencies has prompted much research recently into the aluminium nitride/gallium nitride high electron mobility transistors (AlN/GaN HEMTs) in response to theoretical predictions of higher performance devices. Despite having superior material properties such as higher two-dimensional electron gas (2DEG) densities and larger breakdown field as compared to the conventional aluminium gallium nitride (AlGaN)/GaN HEMTs, the AlN/GaN devices suffer from surface sensitivity, high leakage currents and high Ohmic contact resistances. Having very thin AlN barrier layer of ∼ 3 nm makes the epilayers very sensitive to liquids coming in contact with the surface. Exposure to any chemical solutions during device processing degrades the surface properties, resulting in poor device performance. To overcome the problems, a protective layer is employed during fabrication of AlN/GaN-based devices. However, in the presence of the protective/passivation layers, formation of low Ohmic resistance source and drain contact becomes even more difficult. In this work, thermally grown aluminium oxide (Al2O3) was used as a gate di- electric and surface passivation for AlN/GaN metal-oxide-semiconductor (MOS)-HEMTs. Most importantly, the Al2O3 acts as a protection layer during device processing. The developed technique allows for a simple and effective wet etching optimisation using 16H3PO4:HNO3:2H2O solution to remove Al from the Ohmic contact regions prior to the formation of Al2O3 and Ohmic metallisation. Low Ohmic contact resistance (0.76Ω.mm) as well as low sheet resistance (318Ω/square) were obtained after optimisation. Significant reduction in the gate leakage currents was observed when employing an additional layer of thermally grown Al2O3 on the mesa sidewalls, particularly in the region where the gate metallisation overlaps with the exposed channel edge. A high peak current ∼1.5 A/mm at VGS=+3 V and a current-gain cutoff frequency, fT , and maximum oscillation frequency, fMAX , of 50 GHz and 40 GHz, respectively, were obtained for a device with 0.2 μm gate length and 100 μm gate width. The measured breakdown voltage, VBR, of a two-finger MOS-HEMT with 0.5μm gate length and 100 μm gate width was 58 V. Additionally, an approach based on an accurate estimate of all the small-signal equivalent circuit elements followed by optimisation of these to get the actual element values was also developed for AlN/GaN MOS-HEMTs. The extracted element values provide feedback for further device process optimisation. The achieved results indicate the suitability of thermally grown Al2O3 for AlN/GaN-based MOS-HEMT technology for future high frequency power applications

INVESTIGATION OF RELIABILITY IN GALLIUM NITRIDE HIGH ELECTRON MOBILITY TRANSISTORS USING EQUIVALENT CIRCUIT MODELS FOR USE IN HIGH POWER, HIGH FREQUENCY MICROWAVE AMPLIFIERS

Gallium Nitride (GaN) is beginning to emerge as an alternative to the Gallium Arsenide in high power, high frequency microwave communications. Other novel semiconductors show potential at higher frequency applications. The largest obstacles to GaN emerging as the dominant microwave semiconductor are the issue of cost, which could be reduced through volume, and question of reliability. A new approach to the analysis of reliability has been developed based on the periodic generation of equivalent circuit models while a device is stressed in a manner that is similar to performance likely to be seen during commercial operation. Care was made in this research to ensure that the stress measurements used to induce degradation are as close as possible to those that would degrade a device in real world applications. Equivalent circuit models (ECM) can be used to simulate a device in computer aided design (CAD) software, but these models also provide a picture of the physical properties within the device at a specific point in time. The periodic generation of ECMs allows the researcher to understand the physical changes in the device over time by performing non-destructive electronic measurements. By analyzing the changes in device performance, the physical mechanism of device degradation can be determined. A system was developed to induce degradation and perform measurements of sufficient detail to produce a large signal ECM. Software for producing the ECM was also created. The changes in the ECM were analyzed to diagnose the physical changes in the device under test (DUT) and to identify a method of degradation. The information acquired from this system can be used to improve the device manufacturing process at the foundry. It can also be used to incorporate device degradation into the operation of systems

Caracterização, modelação e compensação de efeitos de memória lenta em amplificadores de potência baseados em GAN HEMTS

Gallium nitride (GaN) high-electron-mobility transistors (HEMTs) have emerged as the most compelling technology for the transmission of highpower radio-frequency (RF) signals for cellular mobile communications and radar applications. However, despite their remarkable power capabilities, the deployment of GaN HEMT-based RF power amplifiers (PAs) in the mobile communications infrastructure is often ruled out in favor of alternative siliconbased technologies. One of the main reasons for this is the pervasiveness of nonlinear long-term memory effects in GaN HEMT technology caused by thermal and charge-trapping phenomena. While these effects can be compensated for using sophisticated digital predistortion algorithms, their implementation and model-extraction complexity—as well as the power necessary for their real-time execution—make them unsuitable for modern small cells and large-scale multiple-input multiple-output transceivers, where the power necessary for the linearization of each amplification element is of great concern. In order to address these issues and further the deployment of high-powerdensity high-efficiency GaN HEMT-based RF PAs in next-generation communications and radar applications, in this thesis we propose novel methods for the characterization, modeling, and compensation of long-term memory effects in GaN HEMT-based RF PAs. More specifically, we propose a method for the characterization of the dynamic self-biasing behavior of GaN HEMTbased RF PAs; multiple behavioral models of charge trapping and their implementation as analog electronic circuits for the accurate real-time prediction of the dynamic variation of the threshold voltage of GaN HEMTs; a method for the compensation of the pulse-to-pulse instability of GaN HEMT-based RF PAs for radar applications; and a hybrid analog/digital scheme for the linearization of GaN HEMT-based RF PAs for next-generation communications applications.Os transístores de alta mobilidade eletrónica de nitreto de gálio (GaN HEMTs) são considerados a tecnologia mais atrativa para a transmissão de sinais de radiofrequência de alta potência para comunicações móveis celulares e aplicações de radar. No entanto, apesar das suas notáveis capacidades de transmissão de potência, a utilização de amplificadores de potência (PAs) baseados em GaN HEMTs é frequentemente desconsiderada em favor de tecnologias alternativas baseadas em transístores de silício. Uma das principais razões disto acontecer é a existência pervasiva na tecnologia GaN HEMT de efeitos de memória lenta causados por fenómenos térmicos e de captura eletrónica. Apesar destes efeitos poderem ser compensados através de algoritmos sofisticados de predistorção digital, estes algoritmos não são adequados para transmissores modernos de células pequenas e interfaces massivas de múltipla entrada e múltipla saída devido à sua complexidade de implementação e extração de modelo, assim como a elevada potência necessária para a sua execução em tempo real. De forma a promover a utilização de PAs de alta densidade de potência e elevada eficiência baseados em GaN HEMTs em aplicações de comunicação e radar de nova geração, nesta tese propomos novos métodos de caracterização, modelação, e compensação de efeitos de memória lenta em PAs baseados em GaN HEMTs. Mais especificamente, nesta tese propomos um método de caracterização do comportamento dinâmico de autopolarização de PAs baseados em GaN HEMTs; vários modelos comportamentais de fenómenos de captura eletrónica e a sua implementação como circuitos eletrónicos analógicos para a previsão em tempo real da variação dinâmica da tensão de limiar de condução de GaN HEMTs; um método de compensação da instabilidade entre pulsos de PAs baseados em GaN HEMTs para aplicações de radar; e um esquema híbrido analógico/digital de linearização de PAs baseados em GaN HEMTs para comunicações de nova geração.Programa Doutoral em Telecomunicaçõe

ELECTRON DEVICE NONLINEAR MODELLING FOR MICROWAVE CIRCUIT DESIGN

The electron device modelling is a research topic of great relevance, since the performances required to devices are continuously increasing in terms of frequency, power and linearity: new technologies are affirming themselves, bringing new challenges for the modelling community. In addition, the use of monolithic microwave integrated circuits (MMIC) is also increasing, making necessary the availability, in the circuit design phase, of models which are computationally efficient and at the same more and more accurate. The importance of modelling is even more evident by thinking at the wide area covered by microwave systems: terrestrial broadband, satellite communications, automotive applications, but also military industry, emergency prevention systems or medical instrumentations. This work contains a review of the empirical modelling approach, providing the description of some well-known equivalent-circuit and black-box models. In addition, an original modelling approach is described in details, together with the various possible applications: modelling of nonquasi-static phenomena as well as of low-frequency dispersive effects. A wide experimental validation is provided, for GaAs- and GaN-based devices. Other modelling issues are faced up, like the extraction of accurate models for Cold-FET or the more convenient choice of the data-interpolator in table-based models. Finally, the device degradation is also treated: a new measurement setup will be presented, aimed to the characterization of the device breakdown walkout under actual operating conditions for power amplifiers

Towards a More Flexible, Sustainable, Efficient and Reliable Induction Cooking: A Power Semiconductor Device Perspective

Esta tesis tiene como objetivo fundamental la mejora de la flexibilidad, sostenibilidad, eficiencia y fiabilidad de las cocinas de inducción por medio de la utilización de dispositivos semiconductores de potencia: Dentro de este marco, existe una funcionalidad que presenta un amplio rango de mejora. Se trata de la función de multiplexación de potencia, la cual pretende resolverse de una manera más eficaz por medio de la sustitución de los comúnmente utilizados relés electromecánicos por dispositivos de estado sólido. De entre todas las posibles implementaciones, se ha identificado entre las más prometedoras a aquellas basadas en dispositivos de alta movilidad de electrones (HEMT) de Nitruro de Galio (GaN) y de aquellas basadas en Carburo de Silicio (SiC), pues presentan unas características muy superiores a los relés a los que se pretende sustituir. Por el contrario, otras soluciones que inicialmente parecían ser muy prometedoras, como los MOSFETs de Súper-Unión, han presentado una serie de comportamientos anómalos, que han sido estudiados minuciosamente por medio de simulaciones físicas a nivel de chip. Además, se analiza en distintas condiciones la capacidad en cortocircuito de dispositivos convencionalmente empleados en cocinas de inducción, como son los IGBTs, tratándose de encontrar el equilibrio entre un comportamiento robusto al tiempo que se mantienen bajas las pérdidas de potencia. Por otra parte, también se estudia la robustez y fiabilidad de varios GaN HEMT de 600- 650 V tanto de forma experimental como por medio de simulaciones físicas. Finalmente se aborda el cálculo de las pérdidas de potencia en convertidores de potencia resonantes empleando técnicas de termografía infrarroja. Por medio de esta técnica no solo es posible medir de forma precisa las diferentes contribuciones de las pérdidas, sino que también es posible apreciar cómo se distribuye la corriente a nivel de chip cuando, por ejemplo, el componente opera en modo de conmutación dura. Como resultado, se obtiene información relevante relacionada con modos de fallo. Además, también ha sido aprovechar las caracterizaciones realizadas para obtener un modelo térmico de simulación.This thesis is focused on addressing a more flexible, sustainable, efficient and reliable induction cooking approach from a power semiconductor device perspective. In this framework, this PhD Thesis has identified the following activities to cover such demands: In view of the growing interest for an effective power multiplexing in Induction Heating (IH) applications, improved and efficient Solid State Relays (SSRs) as an alternative to the electromechanical relays (EMRs) are deeply investigated. In this context, emerging Gallium Nitride (GaN) High‐Electron‐Mobility Transistors (GaN HEMTs) and Silicon Carbide (SiC) based devices are identified as potential candidates for the mentioned application, featuring several improved characteristics over EMRs. On the contrary, other solutions, which seemed to be very promising, resulted to suffer from anomalous behaviors; i.e. SJ MOSFETs are thoroughly analysed by electro‐thermal physical simulations at the device level. Additionally, the Short Circuit (SC) capability of power semiconductor devices employed or with potential to be used in IH appliances is also analysed. On the one hand, conventional IGBTs SC behavior is evaluated under different test conditions so that to obtain the trade‐off between ruggedness and low power losses. Moreover, ruggedness and reliability of several normally‐off 600‐650 V GaN HEMTs are deeply investigated by experimentation and physics‐based simulation. Finally, power losses calculation at die‐level is performed for resonant power converters by means of using Infrared Thermography (IRT). This method assists to determine, at the die‐level, the power losses and current distribution in IGBTs used in resonant soft‐switching power converters when functioning within or outside the Zero Voltage Switching (ZVS) condition. As a result, relevant information is obtained related to decreasing the power losses during commutation in the final application, and a thermal model is extracted for simulation purposes.<br /

Characterization of Microwave Transistors for Robust Receivers and High Efficiency Transmitters

The next generation of integrated transceiver front-ends needs both robust low noise amplifiers and high power amplifiers on a single-chip. The Aluminium Gallium Nitride / Gallium Nitride (AlGaN/GaN) High Electron Mobility Transistors (HEMT) is a suitable semiconductor technology for this purpose due to its high breakdown voltage and high electron mobility. In this thesis the AlGaN/GaN HEMT’s thermal properties, noise and survivability have been characterized for the intended use in robust high power transceivers. Furthermore, a new characterization setup for load modulated high efficiency power amplifiers have been developed. The thermal properties of AlGaN/GaN HEMTs have been carefully investigated considering self-heating and its effect on small-signal parameters and high frequency noise. Self-heating is a severe problem for a high power transistor on any semiconductor material, including GaN. In addition to reliability problems, the performance of the operating HEMT degrades with temperature. The access resistances showed a large temperature dependence, which was also verified with TLM measurements. Due to the large self-heating, the temperature dependence of the access resistances has to be taken into account in the modeling of the AlGaN/GaN HEMT. A temperature dependent small-signal noise model was derived and verified through fabricated amplifiers. Design strategies for robust low noise amplifiers are discussed and implemented using the derived model. The new characterization setup gives new possibilities to characterize the performance of load modulated amplifiers. Recent results on load modulated amplifiers show promising efficiency improvements in back-off operation. Therefore a new measurement setup was developed that performs dynamic load modulation at the transistor terminals. This method should be useful to further improve the performance of load modulated amplifiers for high efficiency operation. The measurement setup is based on an active load-pull setup, where a modulated input signal is used to synthesize a time varying output power. The load impedance is dynamically controlled with the envelop of the input signal, following an optimum efficiency load trajectory. This gives better insight into device operation and possible improvements

On-line Condition Monitoring, Fault Detection and Diagnosis in Electrical Machines and Power Electronic Converters

The objective of this PhD research is to develop robust, and non-intrusive condition monitoring methods for induction motors fed by closed-loop inverters. The flexible energy forms synthesized by these connected power electronic converters greatly enhance the performance and expand the operating region of induction motors. They also significantly alter the fault behavior of these electric machines and complicate the fault detection and protection. The current state of the art in condition monitoring of power-converter-fed electric machines is underdeveloped as compared to the maturing condition monitoring techniques for grid-connected electric machines. This dissertation first investigates the stator turn-to-turn fault modelling for induction motors (IM) fed by a grid directly. A novel and more meaningful model of the motor itself was developed and a comprehensive study of the closed-loop inverter drives was conducted. A direct torque control (DTC) method was selected for controlling IM’s electromagnetic torque and stator flux-linkage amplitude in industrial applications. Additionally, a new driver based on DTC rules, predictive control theory and fuzzy logic inference system for the IM was developed. This novel controller improves the performance of the torque control on the IM as it reduces most of the disadvantages of the classical and predictive DTC drivers. An analytical investigation of the impacts of the stator inter-turn short-circuit of the machine in the controller and its reaction was performed. This research sets a based knowledge and clear foundations of the events happening inside the IM and internally in the DTC when the machine is damaged by a turn fault in the stator. This dissertation also develops a technique for the health monitoring of the induction machine under stator turn failure. The developed technique was based on the monitoring of the off-diagonal term of the sequence component impedance matrix. Its advantages are that it is independent of the IM parameters, it is immune to the sensors’ errors, it requires a small learning stage, compared with NN, and it is not intrusive, robust and online. The research developed in this dissertation represents a significant advance that can be utilized in fault detection and condition monitoring in industrial applications, transportation electrification as well as the utilization of renewable energy microgrids. To conclude, this PhD research focuses on the development of condition monitoring techniques, modelling, and insightful analyses of a specific type of electric machine system. The fundamental ideas behind the proposed condition monitoring technique, model and analysis are quite universal and appeals to a much wider variety of electric machines connected to power electronic converters or drivers. To sum up, this PhD research has a broad beneficial impact on a wide spectrum of power-converter-fed electric machines and is thus of practical importance