Analytical Model And Characteristics Of Trench SOI LDMOS Device

LDMOS(Lateral Double-diffused MOSFET)is a power device with high performance-price ratio in high-voltage integrated circuit applications.It has always been aimed at achieving high breakdown voltage and low specific on-resistance.Up to now,the research on LDMOS focuses on the development of new technologies and new structures.For the model study,the surface electric field of the device is mainly concerned,and the theoretical analysis of the electric field distribution and breakdown voltage is still lacking.In this paper,the analytical model of conventional trench SOI LDMOS and LDMOS with highly doped N/P pillars parallel to the trench is proposed.The theoretical reference for designing the depth and width of trench and doping concentration is presented.On this basis,the new structure of variable-k dielectric trench LDMOS is proposed,which further alleviates the contradictory between breakdown voltage and specific on-resistance.Firstly,the relationship between the structure parameters,the doping concentration of the drift region and the breakdown voltage of conventional trench LDMOS devices is analyted.And the analytical model of potential and electric field distribution on both sides of the dielectric trench is established based on the solution of the two-dimensional Poisson's equation.Then the Schwartz-Chrissfield(S-C)transformation is utilized to regularize the boundary conditions under the trench of the trench LDMOS with highly doped N/P pillars.The parabolic approximation is used to transform the Poisson equation into a convenient differential equation.Based on the analytical model of the conventional trench LDMOS,the potential and electric field model of the silicon region of the N/P trench SOI LDMOS are established,and an approximate model of the optimized breakdown voltage is obtained.The TCAD simulation results show that the model can accurately predict the impact of key parameters on the characteristics.It can also provide a theoretical basis for in-depth study of the working mechanism of the device,optimizing the device parameters,and improving the breakdown voltage.Finally,the new structure of variable-k dielectric trench LDMOS(TD-LDMOS and TT-LDMOS)and variable-k dielectric trench LDMOS with highly doped parallel N/P pillars on both sides of the trench(TDP-LDMOS and TTP-LDMOS)are proposed.These new structures increase the surface electric field by filling the low-k material on the top of the trench.The relatively high-k material is employed on the bottom of the trench to increase the average relative dielectric constant of the trench.Consequently,the breakdown voltage increases,the cell size of the device reduces and the specific on-resistance decreases.The simulation results show that the performance of the trench LDMOS with three-layer trench is improved compared to the LDMOS with two-layer trench in the same size parameters.Among them,the LDMOS with three-layer trench and high doped N/P pillars has the highest figure of merit,with a breakdown voltage of 601 V and a specific on-resistance of 41.8m?·cm~2.