Fast-switching monolithically integrated high-voltage GaN-on-Si power converters

The lateral, high-voltage aluminum gallium nitride (AlGaN)/GaN-on-silicon (Si) technology allows the design of efficient, fast switching high-voltage transistors due to the excellent physical properties of the wide bandgap material GaN and the high conductivity of the AlGaN/GaN heterojunction. Furthermore, the lateral structure of this technology facilitates the integration of multiple power devices and control logic on a single die without additional complex processing steps compared to single switches. Both attributes together allow the design of switches and integrated circuits (ICs) with high power densities for operation at high switching frequencies, and thus enable the reduction of the overall power converter size. This work investigates and demonstrates the potential of monolithic integration of multiple power switches, fabricated in a AlGaN/GaN-on-Si technology. The associated challenges are examined, and guidelines for further developments are proposed. It is shown that only with monolithic integration and appropriate assembly techniques, the full potential of this high-performance, cost-efficient material compound can be released. Monolithically integrated circuits show outstanding performance for fast switching operation due to low intrinsic parasitics resulting from the compact design. Combined with the development of appropriate assembly techniques, high-frequency, high-power converter operation of GaN-power ICs is enabled. In this work two topologies are integrated and their operation demonstrated: the most widely used intrinsic power electronics topology - a half-bridge - and a more complex diode-clamped multilevel converter topology. Compared to vertical devices, lateral switches possess an additional degree of freedom: the control via the backside contact. The voltage control at this contact is important for keeping high performance of the power switches over a wide operating range. Thus, the influence of high positive and negative voltages across the GaN-buffer on the conductivity of the device is systematically investigated. For the first time, it is demonstrated that the coupling across this substrate contact is the major issue for high-voltage, monolithically integrated circuits, which share a common substrate