The influence of the N⁺ floating layer on the drift doping of RESURF LDMOS and its analytical model

Abstract

The influence of the N⁺ floating layer on the drift doping of RESURF LDMOS is studied in this paper. By optimizing the electric field distribution, a new RESURF criterion for LDMOS with N⁺ floating layer is developed as: N_Dt_S ≤ 0.83 × 10¹² cm⁻² (N_D and t_S are the drift doping and thickness, respectively). The optimal drift doping is smaller than that of Single RESURF LDMOS (N_Dt_S ≤ 1.4 × 10¹² cm⁻²). Both analytical and numerical results show the N⁺ floating layer can be used to increase the breakdown voltage of LDMOS but at the cost of a low drift doping and a large on-resistance. The effect of the N⁺ floating layer on REBULF LDMOS is also studied in some detail. This model can be used in the design of RESURF and REBULF LDMOS to optimize the doping concentration of the drift region.