High Voltage Gallium Oxide MOSFET for Power Switching Applications
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Achieving higher energy efficiency and more compact size in electronic devices is the perpetual theme in the power electronics field. In the recent decade, Ga2O3 has attracted a lot of attention and is deemed to be the next generation ultra-wide bandgap (UWBG) power semiconductor to revolutionize the entire field, owing to the high critical strength and hence high Baliga’s figure of merit (BFoM). In this thesis, a record high performance β-gallium oxide (β-Ga2O3) metal-oxide-semiconductor field effect transistor (MOSFET) with breakdown voltage Vbr= 1975V and on-resistance Ron= 520mΩ·cm2 has been reported. It has one of the highest power figure of merit (PFoM) among the recently reported ~2kV devices and marks an important milestone towards the realization of high performance β-Ga2O3 MOSFETs. The device used SiO2 as gate dielectric to improve high temperature performance. Therefore, the properties at SiO2/Ga2O3 interface, including conduction band offset and interface state density, are systematically studied here. The spin-on-glass (SOG) doping technique is used to form a low resistance ohmic contact in the source and drain electrode, the procedures, conditions, and results in the experiments are reported as well. For the device, a field plate is used to improve the breakdown voltage of the Ga2O3 MOSFET. Simulation is performed to reveal the optimum design for the field plate. The field plated β-Ga2O3 MOSFET is fabricated with both SOG source/drain (S/D) doping technique and using an S/D ohmic capping layer. The breakdown in the device is found out to be extrinsic in the device ambient instead of the avalanching breakdown inside the Ga2O3 channel, much lower than what’s expected from the simulation. A theory describing the extrinsic breakdown mechanism is then proposed to explain the breakdown data.