A new analytical model for optimizing SOI LDMOS with step doped drift region

In this paper, a new theoretical breakdown model of SOI RESURF LDMOS with step drift doping profile is proposed. According to this model, the 2-D electric field distributions of drift regions are investigated for both the incompletely and completely depleted cases. The doping profile and step number are optimized to improve the breakdown voltage and reduce fabrication cost. Finally, SOI LDMOS with various step numbers have been made using a 3 μm-thick top silicon layer and a 1.5 μm-thick buried oxide layer. The experiment results indicate that two-step drift doping can enable increase in the breakdown voltage by as much as 40% and decrease in the on-resistance by as much as 16% in comparison to the conventional LDMOS with uniformly doped drift region.