Research Of Short-circuit Reliability Of Sic Trench Power MOSFET

Si C-Trench-Power-MOSFET has the advantages of high critical breakdown electric field,high current density,high thermal conductivity,and has a wide range of application prospects.The Si C-Trench-Power-MOSFET has vertical channels which effectively reduce the cell area and increase the current density of the device.However,the electric field concentration at the corner of the trench makes the gate oxide face more severe reliability problems.Short-circuit(SC)-induced instability is one of the most serious reliability issues because high voltage and current are applied to the device simultaneously,resulting in extremely high power dissipation.Degradation or failure will occur within a few microseconds,which will affect the normal operation of the system.Therefore,it is of great significance to conduct in-depth research on the short-circuit reliability of Si C-Trench-Power-MOSFET.A comprehensive study on the short-circuit reliability of Si C-Trench-Power-MOSFET is completed in this research.With the help of short-circuit test platform and TCAD simulation platform,the ultimate short-circuit failure mechanism of trench-type devices is revealed,and the damage location of the gate oxide is accurately located by the segmented CV method.The results show that the current accumulation at the corners of the trench will cause a high impact ionization rate under the ultimate short-circuit stress.The holes generated by the impact are injected into the gate oxide under the action of the electric field,causing damage to the gate oxide near the drain terminal.In addition,the gate oxide near the source terminal will be damaged at high temperatures,resulting in short-circuiting during the gate and source.The device loses its gate control capability.In this thesis,the repeated short-circuit reliability of Si C-Trench-Power-MOSFET is also studied by means of accelerated degradation.It is found that positive charges are continuously injected into the gate oxide layer under repeated short-circuit stress.It makes the stray capacitance continue to increase although the device did not lose the gate control capability immediately.At the same time,the leakage current of the body diode continues to rise under repeated short-circuit stress,resulting in a continuous decrease of the blocking characteristics of the device.Based on the research above,a prediction model is established for assessing the repeated short circuit withstand times of Si C-Trench-Power-MOSFET,and the accuracy of the model is greater than 90%.At the same time,the thickness of the gate oxide of Si C-Trench-Power-MOSFET is optimized,which reduces the current density and impact ionization rate at the corners of the trench.It effectively improves the short-circuit reliability of the device.