A Superjunction LDMOS with Steps Buried Oxide

Abstract

A superjunction (SJ) LDMOS with steps buried oxide (SBOX) is proposed in this paper. The SJ LDMOS with SBOX designed is based on the Enhanced Dielectric Field (ENDIF). The drift region is divided into three parts according to the depths of the SBOX, which gradually increases from source to drain in order to optimize the drift region charge distributions and shield the substrate assisted depletion (SAD) effect. With this design, the SJ reaches the charge balance and increases the lateral breakdown voltage (BV) of the device. Furthermore, the SBOX can also fix holes so that the hole concentrations of the SBOX upper interface are greatly increased, and it increases the vertical electric field. In this way, the BV of the device is increased and the tradeoff between the BV and specific on-resistance (Ron,sp) is achieved. Compared with a conventional SOI SJ LDMOS at the same 14 μm drift region length, the BV of the SBOX SJ LDMOS is increased from 207.1 V to 296.9 V and the figure of merit (FOM) is enhanced from 4.5 MW cm−2 to 9.9 MW cm−2.