SOI LDMOS with variable-k dielectric trench

An SOI LDMOS with a variable-k dielectric trench (VKTLDMOS) is proposed. The low-k dielectric on the top of the trench is used to sustain high voltage and ensure the smallest cell pitch while the high-k dielectric on the bottom of the trench increases the average permittivity of the trench and increases the drift doping. The SiO₂ dielectric is in the middle of the high-k and low-k materials. Moreover, the SOI TLDMOS with a different k filling dielectric is also discussed. The high-k dielectric is suitable to fill a shallow and wide trench while the low-k dielectric is suitable for a deep and narrow trench. Simulation shows the VKTLDMOS has the highest FOM BV²/R_s,on compared with that of the conventional SOI TLDMOS.