Improving breakdown performance for novel LDMOS using n + floating islands in substrate

Abstract

A novel lateral double-diffusion MOS (LDMOS) with n+ floating islands in the substrate (NFI LDMOS) is proposed. In the NFI LDMOS, a series of n+ floating islands are introduced into the substrate. On the condition of a high-voltage blocking state, n+ floating islands induce the high potential from the drain region to the source region, which modulates the drift region's electric field and leads to a higher breakdown voltage (BV). What is more, the specific on-resistance (R on,sp) is reduced by the higher doping concentration of the drift region due to the n+ floating islands. Compared with the conventional LDMOS at the same 40 μm drift region, the BV of the NFI LDMOS is enhanced by 74.6% and R on,sp is reduced by 19.7%. So, the proposed NFI LDMOS possesses a higher figure-of-merit (FOM).