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Link visio: https://univ-grenoble-alpes-fr.zoom.us/j/96244599961?pwd=bS9BWGZ6VjBKM0dsTWJWeUYzTkN5dz09
Meeting ID: 962 4459 9961 / Passcode: 885306
The defence will be in English.
Abstract: Increasing population density within compact urban regions, when juxtaposed with the preferred decentralized electricity generation and its increasing demand, underscores the necessity of enhancing our electrical transport and conversion infrastructures, particularly in light of the challenges posed by its storage. Silicon-based power devices, which currently form the backbone of various conversion stages, have nearly reached their theoretical limits and the only road to improve their performance is to use new materials with better properties. Among potential candidates, diamond with outstanding physical properties is the ultimate semiconductor for power electronics that couple high power handling, high switching frequency, low losses and high thermal management capabilities. Besides being the hardest material, diamond possesses the best properties among ultra-wide band gap semiconductors including its high electron-hole mobility (1060-2100 cm²/V.s respectively), high critical electric field (> 10 MV/cm) and high thermal conductivity (22 W/cm.K). Thanks to its exceptional physical properties diamond offers novel opportunities for a wide range of multi-disciplinary application, extending beyond to, but potentially compatible with, power electronics, like: localized electric, optic and magnetic signal probing, reliable data processing, and secure communication in both harsh and in-vivo biological environments. The development of diamond devices capable of non-volatile charge storage and individual embedded devices addressing is essential for creating monolithic diamond-based systems, highly beneficial for future intelligent power conversion system implantable in smart grids or aerospace harsh environment. Despite several technological limitations and bottlenecks that need to be addressed in order to extract diamond’s full potential, like the challenging device fabrication due to small standard substrate size, lab-grown diamond layer quality and dedicated device architecture have made considerable progresses over the last decades.
This thesis is dedicated to the development of large-scale diamond-based Junction Field Effect Transistors (JFET) that can be electro-optically controlled and used as non-volatile memory devices. The optimization of these components, which serve dual purposes, is crucial for the future road-map of diamond technology. Firstly, in the realm of power electronics, there is a need for a true demonstration of large scale diamond devices potential. State-of-the-art devices, often optimized for small active areas, typically excel in either high current density handling or high breakdown field but seldom in combination of both. As a result, devices capable of both conducting 1 A in ON-state and withstanding 1 kV in the OFF state have yet to be demonstrated. On this purpose, the optimization of lateral JFET design especially diamond layer inner properties and inter-digited geometry modelisation has been proposed. Results below initial expectations have been reported but still holding the promise of achievability for the technical specification mentioned herein-above. Secondly, fabrication, characterization and optimization of a diamond-based JFET non volatile photo-switch has been achieved. Since the first demonstration of the structure at the early stage of this thesis, architecture featuring gate contact closer to the active area of the fabricated transistors exhibits better dynamics for equivalent leakage current. Increasing the light collection efficiency of the device by removing non-transparent metallic contact is expected to lower the commutation time of the device by at least one order of magnitude. Additionaly, robustness of the non-volatile OFF state have been reported over more than two days. By combining both functionalities, diamond technology is poised to capture the attention of researchers and companies, thereby driving further development and eventual commercialization.
