Ultralow specific on-resistance high voltage trench SOI LDMOS with enhanced RESURF effect

A RESURF-enhanced high voltage SOI LDMOS（ER-LDMOS） with an ultralow specific on-resistance(Ron,sp) is proposed.The device features an oxide trench in the drift region,a P-pillar at the sidewall of the trench,and a buried P-layer（BPL） under the trench.First,the P-pillar adjacent to the P-body not only acts as a vertical junction termination extension（JTE）,but also forms a vertical reduced surface field（RESURF） structure with the Ndrift region.Both of them optimize the bulk electric field distributions and increase the doping concentration of the drift region.Second,the BPL together with the N-drift region and the buried oxide layer（BOX） exhibits a tripleRESURF effect,which further improves the bulk field distributions and the doping concentration.Additionally,multiple-directional depletion is induced owing to the P-pillar,the BPL,and two MIS-like structures consisting of the N-drift region combined with the oxide trench and the BOX.As a result,a significantly enhanced-RESURF effect is achieved,leading to a high breakdown voltage（BV） and a low Ron,sp.Moreover,the oxide trench folds the drift region in the vertical direction,resulting in a reduced cell pitch and thus Ron,sp Simulated results show that the ER-LDMOS improves BV by 67% and reduces Ron,sp by 91% compared with the conventional trench LDMOS at the same cell pitch.