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 the mechanisms of charge Trapping in GaN Vertical devices

In this master thesis a new type of transistor is analyzed: the GaN Vertical Fin FET Transistor. This kind of transistor is made on GaN, a wide bandgap semiconductor which is a promising material for the future power electronics . Fin FET Transistor is based on a fin-architecture and the current flows vertically through a GaN made nanometer-sized channel having a MOS stack on the sides. In this work different measurements are performed in order to see the variation of the threshold voltage and channel resistance of the transistor varying the fin width and external parameters such as temperature and exposure to UV-light. Oxide trapping phenomena are analysed by applying to the gate an increasing positive bias potential and for increasing periods of time. Simulations are performed in order to further analyze the results and give an extensive explanation of the charge trapping behaviour in different bias conditions.ope

Estudio de la fiabilidad de los dispositivos HEMT de GaN

El presente trabajo de tesis en Ingeniería Electrónica tiene como objetivo el estudio de la fiabilidad de dispositivos HEMT (High Electron Mobility Transistor) de GaN (Gallium Nitride). Gracias a las ventajas teóricas en el uso de dispositivos GaN frente a dispositivos de Silicio y a la aparición de dispositivos GaN que mejoran las prestaciones de sus homónimos de Silicio, el siguiente paso, es el estudio de la fiabilidad que presentan estos dispositivos en la actualidad, con el objetivo de mejorarlos e investigar los límites actuales en determinadas aplicaciones de potencia. La investigación realizada en esta tesis se divide en tres partes claramente diferenciadas. La primera de ellas trata el estudio del principal problema asociado a la tecnología de los HEMT de GaN de cara a su funcionamiento en conmutación: la resistencia dinámica. Este ha sido un problema muy estudiado desde los inicios de la realización de los HEMT de GaN para aplicaciones de potencia, que a día de hoy sigue siendo uno de los principales problemas a resolver en estos dispositivos. En esta tesis se han estudiado distintos dispositivos comerciales, donde se demuestran que un buen diseño estructural del dispositivo GaN HEMT es imprescindible para evitar problemas asociados a la resistencia dinámica. Mientras unos fabricantes continúan presentando este problema en sus dispositivos, otros fabricantes han conseguido minimizarlo mediante modificaciones en la estructura. La segunda parte engloba el análisis y los resultados obtenidos desde un punto de vista de la fiabilidad eléctrica, o también conocido como robustez de estos dispositivos. Esta segunda parte engloba las pruebas para determinar la capacidad de soportar cortocircuitos y avalanchas por sobretensión. Análisis, que es de aplicación directa de cara al funcionamiento real de los dispositivos GaN HEMT como transistores de potencia en el campo industrial. Los resultados obtenidos en esta tesis muestran que los dispositivos HEMT de GaN no tienen un buen comportamiento frente a eventos de avalancha y a priori no parece un problema con una solución inmediata. Sin embargo, los dispositivos HEMT de GaN analizados en cortocircuito si demuestran un buen comportamiento ante condiciones de cortocircuito. A pesar de la necesidad de mejoras, que están relacionadas con el efecto de los electrones calientes (hot-electron) los dispositivos HEMT de GaN han conseguido soportar tiempos de cortocircuito mucho mayores que sus competidores de Silicio. Por último, la tercera parte engloba las pruebas relacionadas con la necesidad asociada al uso de estos dispositivos en la industria aeroespacial, analizando la robustez y comportamiento ante radiación electromagnética. Esta última parte de estudio, demuestra que el diseño y geometría de la estructura juega un papel esencial en el comportamiento de los dispositivos HEMT de GaN frente a radiación. Además, todos los cambios observados tras la radiación de los dispositivos HEMT de GaN están relacionados con efectos de atrapamiento/desatrapamiento de cargas en los dispositivos. Por este motivo, los dispositivos que han demostrado estar libres de este atrapamiento durante los test de resistencia dinámica, han demostrado ser robustos frente a radiación y no han sufrido cambios tras la misma, independientemente del uso de dosis altas o bajas de radiación gamma. Por tanto, los resultados obtenidos durante esta tesis muestran a los HEMT de GaN como dispositivos prometedores, que se encuentran ya muy cerca de su uso en aplicaciones reales, pero que todavía tiene aspectos tecnológicos, de cara a su implantación en los diseños de potencia actuales (tales como el encapsulado, circuitos de disparo, etc.), que se espera, vayan mejorándose con la evolución de los procesos de diseño y fabricación.The theoretical advantages of GaN devices compared to its Silicon counterparts has been extensively studied and confirmed over the last decade. Following these studies, the current thesis is made with the aim of studying the current reliability of commercial GaN devices to contribute the future improvement of these devices from the point of view of its application in the future of power electronics. The research carried out in this thesis is divided into three clearly differentiated parts. The first part is about the main problem associated with the GaN HEMT technology from its beginning and is known as dynamic resistance. This problem has been extensively studied in the literature over the last decades and still being today one of the main problems associated to the GaN HEMTs. This thesis studies this phenomenon over different commercial GaN devices. These studies show that a good structural design of the GaN HEMT is mandatory to avoid problems causing dynamic resistance. While some manufacturers still showing this problem on its HEMTs, others have managed to reduce it with new structural designs. The second part of this thesis corresponds to the analysis and results from a point of view of the electrical reliability, also known as robustness of the GaN HEMT devices. This second part it’s about the capability of the device to endure short-circuits and over-voltages. This part is the closest to the real application of the GaN HEMT devices as power semiconductor in the industrial environment. The results obtained in this thesis show that GaN HEMT devices do not show a good behavior with avalanche events and it does not seem to have an immediate solution. However, GaN HEMT devices analyzed in short circuit demonstrate good behavior under short circuit conditions. Despite of the need for improvements related with hot-electron effect, the GaN HEMTs have endured short circuit events for times much greater than its Silicon counterparts. As third and last part, this thesis shows the tests related with the needed of the use of these devices at the aerospace industry by analyzing the robustness and behavior against electromagnetic radiation. These studies demonstrate that the design and internal structure of the GaN HEMTs play a main role in the behavior of these devices against radiation. Besides, all the observed changes of the GaN HEMTs are related with charge trapping/detrapping effects. For this reason, the devices that have demonstrated being free current collapse during the dynamic resistance tests have also demonstrated a good behavior against radiation, and its electrical characteristics has not been modified after low and high doses of gamma radiation. Therefore, the obtained results over this thesis show the GaN HEMTs as promising devices for the future of power electronics. They are close to its use in final applications but still being necessary to improve some of their technological aspects for its use in the actual power designs (such as encapsulated, drive circuits …). These aspects are expected to improve with the evolution and improvement of design and manufacturing processes

Feature Papers in Electronic Materials Section

This book entitled "Feature Papers in Electronic Materials Section" is a collection of selected papers recently published on the journal Materials, focusing on the latest advances in electronic materials and devices in different fields (e.g., power- and high-frequency electronics, optoelectronic devices, detectors, etc.). In the first part of the book, many articles are dedicated to wide band gap semiconductors (e.g., SiC, GaN, Ga2O3, diamond), focusing on the current relevant materials and devices technology issues. The second part of the book is a miscellaneous of other electronics materials for various applications, including two-dimensional materials for optoelectronic and high-frequency devices. Finally, some recent advances in materials and flexible sensors for bioelectronics and medical applications are presented at the end of the book

GaN-based power devices: Physics, reliability, and perspectives

Over the last decade, gallium nitride (GaN) has emerged as an excellent material for the fabrication of power devices. Among the semicon- ductors for which power devices are already available in the market, GaN has the widest energy gap, the largest critical field, and the highest saturation velocity, thus representing an excellent material for the fabrication of high-speed/high-voltage components. The presence of spon- taneous and piezoelectric polarization allows us to create a two-dimensional electron gas, with high mobility and large channel density, in the absence of any doping, thanks to the use of AlGaN/GaN heterostructures. This contributes to minimize resistive losses; at the same time, for GaN transistors, switching losses are very low, thanks to the small parasitic capacitances and switching charges. Device scaling and monolithic integration enable a high-frequency operation, with consequent advantages in terms of miniaturization. For high power/high- voltage operation, vertical device architectures are being proposed and investigated, and three-dimensional structures—fin-shaped, trench- structured, nanowire-based—are demonstrating great potential. Contrary to Si, GaN is a relatively young material: trapping and degradation processes must be understood and described in detail, with the aim of optimizing device stability and reliability. This Tutorial describes the physics, technology, and reliability of GaN-based power devices: in the first part of the article, starting from a discussion of the main proper- ties of the material, the characteristics of lateral and vertical GaN transistors are discussed in detail to provide guidance in this complex and interesting field. The second part of the paper focuses on trapping and reliability aspects: the physical origin of traps in GaN and the main degradation mechanisms are discussed in detail. The wide set of referenced papers and the insight into the most relevant aspects gives the reader a comprehensive overview on the present and next-generation GaN electronics

Advanced III-Nitride Technology for mm-Wave Applications

Within wireless communication, there is a continuously growing need for more bandwidth due to an increasing number of users and data intense services. The development within sensor systems such as radars, is largely driven by the need for increased detection range and robustness. In such systems, power amplification and generation at high frequency are of importance. High-electron mobility transistors based on gallium nitride (GaN HEMTs) offer efficient generation of high output power at high frequency. This is enabled by the unique characteristics of GaN and its heterostructures, with a large breakdown field, related to the wide bandgap, and excellent electron transport properties. Due to this, it is today used in high-performing radar, telecommunications, as well as power electronic systems. Despite substantial progress over the last decade, the GaN HEMT is still the subject of intense research to reach its full potential. \ua0Recent development within epitaxy has significantly improved the quality of III-nitride semiconductors, and enabled indium aluminum nitride (InAlN) and InAlGaN as alternatives to AlGaN in the conventional AlGaN/GaN heterostructure. The higher polarization charge in these materials allows for considerable downscaling of the barrier layer thickness with a sustained high sheet carrier density. \ua0This has opened new possibilities for optimization of the high frequency performance. \ua0\ua0In this work, HEMTs with downscaled InAl(Ga)N barrier layers have been developed with the goal to optimize the devices for power amplification in the mm-wave range. Electron trapping and short-channel effects have been addressed in the design of the epi and in the optimization of the process modules. Different surface passivation layers and deposition methods have been evaluated to mitigate electron trapping at the surface. The output power density of a HEMT increased from 1.7 to 4.1 W/mm after passivation with a SiNx layer. The deposition method for Al2O3 passivation layers showed to have a profound impact on the electron trapping. A layer deposited by plasma-assisted atomic layer deposition (ALD) exhibited superior passivation of the surface traps as compared to the layer deposited by thermal ALD, resulting in an output power at 3 GHz of 3.3, and 1.9 W/mm, respectively. The effect of the channel layer thickness (50 – 150 nm) in InAlGaN/AlN/GaN HEMTs with and AlGaN back barrier demonstrated a trade-off between short-channel effects and deep-level electron trapping in the back barrier. The maximum output power was 5.3 W/mm at 30 GHz, obtained for a GaN layer thickness of 100 nm. To further enhance the high frequency performance, the ohmic contacts were optimized by the development of a Ta-based, Au free, metal scheme. Competitive contact resistance of &lt; 0.2 Ωmm was achieved on both AlGaN/GaN and InAlN heterostructures with a Ta/Al/Ta metal stack. The contacts are annealed at a low temperature (550 – 575 \ubaC) compared to more conventional contact schemes, resulting in a smooth morphology and good edge acuity.\ua0 The implementation of microwave monolithic integrated circuits (MMICs) based on III-nitride HEMTs facilitate the use of III-nitride HEMTs in a system where frequency and compactness are key requirements. Thin film resistors (TFRs) are one of the passive components required in MMICs. In this work, a low-resistance titanium nitride (TiN) TFR was developed as a complement to the higher resistance tantalum nitride (TaN) TFR and mesa resistor in the in-house MMIC process. The developed TiN TFR exhibits a sheet resistance of 10 Ω/□, compared to 50 and 200-300 Ω/□ of the TaN TFR and semiconductor resistor, respectively. The critical dissipated power in the TFR showed a correlation to the footprint area, indicating that Joule-heating was the main cause of failure. TiN- and TaN films exhibit different signs of the thermal coefficient of resistance. This feature was used to demonstrate a temperature compensated TFR (TCR = -60 ppm \ubaC) with application in MMICs operating in a wide temperature range

The 2018 GaN power electronics roadmap

GaN is a compound semiconductor that has a tremendous potential to facilitate economic growth in a semiconductor industry that is silicon-based and currently faced with diminishing returns of performance versus cost of investment. At a material level, its high electric field strength and electron mobility have already shown tremendous potential for high frequency communications and photonic applications. Advances in growth on commercially viable large area substrates are now at the point where power conversion applications of GaN are at the cusp of commercialisation. The future for building on the work described here in ways driven by specific challenges emerging from entirely new markets and applications is very exciting. This collection of GaN technology developments is therefore not itself a road map but a valuable collection of global state-of-the-art GaN research that will inform the next phase of the technology as market driven requirements evolve. First generation production devices are igniting large new markets and applications that can only be achieved using the advantages of higher speed, low specific resistivity and low saturation switching transistors. Major investments are being made by industrial companies in a wide variety of markets exploring the use of the technology in new circuit topologies, packaging solutions and system architectures that are required to achieve and optimise the system advantages offered by GaN transistors. It is this momentum that will drive priorities for the next stages of device research gathered here

The 2018 GaN power electronics roadmap

Gallium nitride (GaN) is a compound semiconductor that has tremendous potential to facilitate economic growth in a semiconductor industry that is silicon-based and currently faced with diminishing returns of performance versus cost of investment. At a material level, its high electric field strength and electron mobility have already shown tremendous potential for high frequency communications and photonic applications. Advances in growth on commercially viable large area substrates are now at the point where power conversion applications of GaN are at the cusp of commercialisation. The future for building on the work described here in ways driven by specific challenges emerging from entirely new markets and applications is very exciting. This collection of GaN technology developments is therefore not itself a road map but a valuable collection of global state-of-the-art GaN research that will inform the next phase of the technology as market driven requirements evolve. First generation production devices are igniting large new markets and applications that can only be achieved using the advantages of higher speed, low specific resistivity and low saturation switching transistors. Major investments are being made by industrial companies in a wide variety of markets exploring the use of the technology in new circuit topologies, packaging solutions and system architectures that are required to achieve and optimise the system advantages offered by GaN transistors. It is this momentum that will drive priorities for the next stages of device research gathered here