Research Of Reliability Of Asymmetric SiC Trench MOSFET

The trench silicon carbide metal-oxide-semiconductor field effect transistor（Si C Trench MOSFET）has the advantages of high breakdown voltage,high current density,low loss,high temperature stability and fast switching speed,which has great application prospects in the new energy vehicles,photovoltaic inverter and other fields.However,as the gate is deep inside the device,the electric field tends to be concentrated at the corner of the trench.Therefore,in practical applications,trench devices will face more severe electrical properties degradation and even failure risks when they are subjected to electrical stresses,such as avalanche,short-circuit and surge-circuit.Therefore,it is of great significance to study the reliability mechanism of trench silicon carbide devices.In this paper,based on the actual stress environment,the reliability mechanisms of trench silicon carbide MOSFET under avalanche stress,short-circuit stress and surge-circuit stress are explored in detail,as follows:（1）It is revealed that the main degradation mechanism of Si C trench MOSFETs under repetitive avalanche stress is the positive charge injection at the gate oxide interface near the trench corner during the avalanche stress process,resulting in negative drift of threshold voltage(V_th)and slight decrease of on-resistance(R_ds（on）),and a significant increase of gate-drain capacitance(C_gd),which affects the switching characteristics of the device,especially the turn-off process,and the turn-off loss increases by 19.02%.（2）It is revealed that the failure mechanism of Si C trench MOSFETs under short-circuit stress is strong impact ionization and high current density in the channel region under short-circuit condition,which together impact the gate oxide layer near the channel region,leading to the damage of the gate oxide layer after being subjected to the 20μs short-circuit stress eventually.（3）It is revealed that the failure mechanism of Si C trench MOSFETs under surge-circuit stress is that charge injection exists at the gate oxide interface at the channel region,which leads to the channel conduction in advance.In a short period of time,large surge-current flows through the channel region of the device,causing a sharp rise in lattice temperature,and the gate oxide layer near the channel will be damaged,resulting in short-circuit of the gate and source,and the device eventually loses its gate control ability.