Electrothermal Analysis of the Charge–Discharge Related Energy Loss of the Output Capacitance in OFF-State Superjunction MOSFETs

Abstract

The charge-discharge-related loss of the output capacitance ( $C_{O}$ ) in off-state Superjunction (SJ) MOSFETs, $E_{DISS}$ , is a new source of energy loss limiting the frequency of soft-switched SJ MOSFETs. This article studies the electrothermal effect in $C_{O}$ during the charging and discharging processes with the help of numerical electrothermal simulations. The results show that energy is lost during both charging and discharging processes, mainly contributed by Joule heat that is caused by the movement of carriers in lightly doped drift regions. The fluctuant doping profile in a SJ MOSFET constructed with the multi-implant multi-epitaxy technology compresses the width of the path of charging and discharging currents at concentration valleys and causes high-current density. Then, its $E_{DISS}$ is larger than that of the SJ MOSFET constructed with the trench-filling epitaxial growth technology. For an advanced device with a smaller cell-pitch, the width of the current path becomes narrower. Then, the current density decreases, and so does its $E_{DISS}$ .