RF LDMOSFET with graded gate structure

Abstract

This paper describes a new RF LDMOS with a graded structure. It enables a very thin gate oxide to be used in the channel region to achieve high transconductance, but at the gate edges, the polysilicon is lifted off to more than 3 times that thickness, and thus the parasitic capacitance values C/sub gd/ and C/sub gs/ are significantly reduced. This improves the RF output power, gain and the cut-off frequency. Due to the release of the electric field in the gate edge, a sufficiently high breakdown voltage can be realized with very thin gate oxide.