High power unipolar fet switch

Abstract

A high power unipolar FET switch has an N− drift layer; a layer of metal contacts the drift layer via an ohmic contact to provide a drain connection for the FET. Each switch cell has a pair of trenches recessed into the drift layer and separated by a mesa region. Oxide layers line the walls and bottom of each trench, which are each filled with a conductive material; the conductive material in each trench is connected together to provide a gate connection for the FET. A shallow P region extends from the bottom of each trench into the drift layer and around the trench corners. A layer of metal contacts the mesa region via an ohmic contact to provide a source connection for the FET. The structure preferably operates as a “normally-off” device, with the potentials created by the work function difference between the conductive material and the N− mesa region completely depleting the mesa region. A positive gate voltage undepletes the mesa regions, creates accumulation channels adjacent to the oxide side-walls of the trenches, and modulates the mesa region, thereby turning the switch on and allowing current to flow between drain and source via the mesa region and the accumulation channels. The switch's unipolar structure enables the device to exhibit a fast switching speed with very low switching losses.