Majority carrier power diode

Abstract

A power diode having substantially no reverse-recovery time and relatively high conductance. The power diode is a majority carrier semiconductor having a structure that is similar to that of a metal oxide semiconductor field effect transistor (MOSFET), in that it includes a source, a drain, a gate, and a body. In one embodiment, to increase conductance of the power diode, a linked-cell configuration that reverses the geometry of a conventional cell-type MOSFET is employed, thereby increasing the width of a conductance channel over that of a conventional MOSFET, and compensating for a relatively low level of inversion in the channel region. Negative and positive feedback circuits are used to further improve the conductance of the power diode by dynamically setting a bias voltage applied between the gate and the source to a level just below a threshold voltage. In the positive feedback circuit, the magnitude of the bias voltage is greater than the threshold voltage if the power diode is forward biased, but substantially reduced if the power diode is reverse biased, thereby minimizing its turn-on delay without risking reverse conductance. Although separate components are used for biasing the device in the disclosed embodiments, it is contemplated that these components be integrated on a common substrate with the source, drain, and gate in a commercially practiced preferred embodiment. Another embodiment employs a charge carrier region diffused into the body and at least in part underlying the gate. This region provides a variable threshold voltage along the channel and reduces the effective length of the channel to increase its conductance. A threshold voltage ranges between a higher value, V.sub.TMAX, adjacent the source, to a lower value, V.sub.T, elsewhere in the device.