A partial-SOI LDMOSFET with triangular buried-oxide for breakdown voltage improvement

In this paper, a near-triangular buried-oxide partial silicon-on-insulator (TB-PSOI) lateral double-diffused MOS field-effect transistor is proposed. The electric field and electrostatic potential in this structure are modified by the gradual buried-oxide thickness increase. The modification includes the addition of a new peak in the electric field in comparison to that of the conventional PSOI. To assess the efficiency of the proposed structure, its breakdown voltage is compared with that of conventional PSOI using two-dimensional simulations. A comparative study is performed in terms of silicon-film and buried-oxide layer thicknesses, drift region and buried-oxide layer lengths, and drift region doping concentrations. The study shows that under the same drain current, the breakdown voltage of TB-PSOI is nearly two times higher than its PSOI counterpart (108% improvement). Simulation results show that the three-stepped oxide layer closely follows the TB-PSOI structure with a breakdown voltage improvement of 96% compared to that of the PSOI structure.