Large-signal and small-signal output capacitances of super junction MOSFETs

Abstract

The small- and large-signal output capacitances of a super junction MOSFET and a conventional power MOSFET are obtained as a function of voltage and compared. The capacitors are charged and discharged by a voltage pulse through an external resistor and the voltage and current across the capacitors are measured as a function of time. The stored charge in the nonlinear output capacitor is shown to be related to the voltage across it in a piecewise nonlinear way as v=aq+bq2 for v<;vlp and v=vlp+c (q-qlp) +d (q-qlp) 2 for v>vlp. The voltage, vlp and the charge, qlp and the constants, a, b, c and d are related to the design of the super junction MOSFET drift region. It is shown experimentally that when the output capacitor associated with the super junction MOSFET is excited by a sinusoidal wave, a large number of harmonics of the fundamental frequency is obtained due to its nonlinearity. The product of the area specific on-resistance and the area specific energy stored in the output capacitor of an advanced super junction MOSFET is shown to be lower than that of a state of the art conventional MOSFET at high voltages.