Research Of The Novel Stucture Of 4H-SIC Superjunction Trench MOSFET

Semiconductor SiC has high critical breakdown electric field,high thermal conductivity and high saturation electron drift speed,which makes them more excellent than Si materials in high temperature,high pressure and high frequency fields.As an ideal candidate for next-generation power switching devices,SiC MOSFETs have the characteristics of high breakdown voltage and low specific on-resistance due to their material advantages.Compared with Si IGBT which is the mainstream switching devices in power electronic circuits,SiC MOSFET has the properties of unipolar conductivity and high saturation electron drift speed which determine their lower switching losses and higher switching speed.Trench gate technology and superjunction technology are used in power MOSFETs to reduce the specific on-resistance.Trench gate technology improves the current capability and reduces the specific on-resistance.Superjunction technology has been used more maturely in silicon.By P/N strip depleting each other,the doping concentration of the drift region is increased,and thus the specific on-resistance is reduced.At the same time,the nonlinear capacitance characteristic of the superjunction reduces the switching loss.However,due to cost and process reliability,superjunction SiC MOSFETs have not yet been commercialized.In this paper,considering the feasibility of introducing superjunction technology into SiC devices,two new structures of 4H-SiC superjunction MOSFETs are proposed,and their static and dynamic characteristics are simulated based on Sentaurus TCAD simulation software:1.A 4H-SiC superjunction double-trench MOSFET（SJ-DTMOS）is proposed.One is floating trench surrounded by P-type strip of the SJ structure,the other is trench gate with a P-type shielding layer below.In the off-state,both the P-type strip and the P-type shield layer deplete the N drift region,which makes the drift region with a high doping concentration fully depleted.Consequently,the drift region has a uniform electric field and high breakdown voltage.In the on-state,the higher drift region doping greatly reduces the on-resistance.Due to the nonlinear capacitance characteristics of the superjunction and the shielding effect of the P-type shielding layer on the gate-drain capacitance,the switching characteristics of the new structure are significantly improved.The simulation results are given as follow:for the proposed SiC MOSFET,the on-resistance R_on,sp=1.07=mΩ·cm² is 51%lower than the traditional DT-MOS;the switching loss E_switch=0.61mJ at 100A/cm² load current is 85%.lower than that of the traditional DT-MOS;2.A 4H-SiC superjunction T-shape trench MOSFET（SJ-TTMOS）is proposed.Compared with SJ-DTMOS,the T-shape trench makes the channel and the P-type strip of the superjunction in the same side of the trench,cancelling the floating trench to form the P-type strip,and reducing the cell pitch.At the same time,the structure adopts an extended P-type shielding region to realize a three-level buffer structure so as to shorten the current path,and thus the short-circuit capability is improved.By simulation,the specific on-resistance R_on,sp=1.14 mΩ·cm² is 43%lower than that of the conventional pT-MOS;the short-circuit time t_sc=11μs is 175%higher than the conventional pT-MOS.