Unclamped inductive switching behaviour of high power SOI vertical DMOS transistors with lateral drain contacts

Abstract

The switching dynamics of silicon-on-insulator (SOI) high power vertical double diffused MOS (VDMOS) transistors with an inductive load has been investigated by device simulation. Unlike other conventional VDMOS devices, this device has drain contacts at the top surface. In general the switching behaviour of a power device during the unclamped inductive switching (UIS) test will determine the reliability of the power device as the energy stored in the inductor during the on state is dumped directly into the device when it is turned off. In this paper we compare the switching dynamics of the SOI VDMOS transistor with standard bulk silicon VDMOS device by doing numerical simulations. It is shown here, using 2D-device simulations that the power dissipated in the SOI VDMOS device during the UIS test is smaller by approximately a factor of 2 than in the standard bulk silicon VDMOSFET. The lower dissipation is due to the presence of the silicon film/buried oxide/substrate structure (this structure forms a SOI capacitor). In the case of the SOI VDMOS transistor the energy released from the inductor during the UIS test is stored to some extent in the SOI capacitor and partly dumped directly into the device. As a result the maximum current through the SOI device is separated in time from the maximum voltage across the device, unlike in the bulk case, thereby reducing the maximum power.