High voltage SOI LDMOS with a compound buried layer

An SOI LDMOS with a compound buried layer (CBL) was proposed. The CBL consists of an upper buried oxide layer (UBOX) with a Si window and two oxide steps, a polysilicon layer and a lower buried oxide layer (LBOX). In the blocking state, the electric field strengths in the UBOX and LBOX are increased from 88 V/μm of the buried oxide (BOX) in a conventional SOI (C-SOI) LDMOS to 163 V/μm and 460 V/μm by the holes located on the top interfaces of the UBOX and LBOX, respectively. Compared with the C-SOI LDMOS, the CBL LDMOS increases the breakdown voltage from 477 to 847 V, and lowers the maximal temperature by 6 K.