a novel silicon rf ldmosfet structure based on the use of a stacked ldd , is disclosed . the ldd has been modified from a single layer of n type material to a stack of three layers . these are upper and lower n type layers with a p type layer between them . the upper n type layer is heavily doped to reduce the on - resistance of the device , while the lower n type layer is lightly doped to reduce the output capacitance , thereby improving the high frequency performance . the middle p layer is heavily doped which allows it to bring about pinch - off of the two n layers , thereby raising the device &# 39 ; s breakdown voltage . a process for manufacturing the device , as well as experimental data concerning its performance are also given .