A new SO1 high-voltage device structure with nonuniform thickness drift region （n-uni SOl） and its optimiza- tion design method are proposed. Owing to the nonuniform thickness drift region, the electric field in the SOl layer is modulated and the electric field in the buried layer is enhanced, resulting in an enhancement of breakdown voltage. An analytical model taking the modulation effect into account is presented to optimize the device structure. Based on the analytical model, the dependencies of the electric field distribution and breakdown voltage on the device parameters are investigated. Numerical simulations support the analytical model. The breakdown voltage of the n-uni SOl LDMOS with n = 3 is twice as high as that of a conventional SO1 while its on-resistance maintains low.
