Analysis And Optimization Of Dynamic Characteristics Of Shielded-gate Trench MOSFET

The shielded-gate trench MOSFET(Metal-Oxide-Semiconductor Field-Effect Transistor)is the mainstream product in medium and low voltage power MOSFETs,and the application of shielded-gate trench MOSFET is further promoted under the guidance of the new energy policy.However,with the increasing power density,shielded-gate trench MOSFET can generate serious switching oscillations due to fast switching speed,which threatens the reliability of the device and even becomes the noise source of electromagnetic interference.Therefore,it is necessary to study the influence of the shielded-gate trench MOSFET on the dynamic switching process.This thesis mainly studies the switching oscillation of the shielded-gate trench MOSFET in the process of inductive load switching and body diode reverse recovery.By changing the structural parameters of the device,the dynamic performance of the device is observed,and the reason is analyzed from the mechanism level and an optimization scheme is proposed.The specific contents are summarized as follows:1.Describe the working state of power MOSFET in inductive load switching circuit,body diode reverse recovery circuit and half-bridge circuit,analyze the mechanism of oscillation during dynamic switching,and summarize the related research contents of shielded-gate trench MOSFET switching oscillation.2.In the inductive load switching circuit,after clarifying the influence of circuit parameters,eight structural parameters such as the resistivity of the drift region are changed.It is found that increasing the resistance of the shielded-gate can significantly suppress the switching oscillation without affecting the power consumption of the device.The resistivity of the drift region,the depth of the trench and the thickness of shielded-gate oxide layer at the bottom of the trench also have a certain influence on the switching oscillation,but the influence of oscillation and power consumption needs to be considered as a compromise.By simulating the C-V characteristic curves of parasitic capacitances with different structural parameters,it is found that larger d C_gd/d V_ds and C_ds can suppress the generation of oscillation in most cases,which is beneficial to guide product selection.3.During the reverse recovery process of the body diode,seven parameters such as the resistivity of the drift region are changed.It is found that the reduction of the trench depth can significantly optimize the body diode performance of the device and the oscillation of the drain-source voltage,and the reduced thickness of the gate oxide can significantly optimize the body diode performance and suppress oscillation to some extent.It is found that the body diode performance of the device is related to two factors,one is the amount of holes injected into the drift region when the body diode is forwardly conducting,and the other is the broadening distance of the depletion layer after reverse extraction.Moreover,the amplitude of the drain-source voltage oscillation generated by the device after the reverse recovery process is completed has a positive correlation with the breakdown voltage of the device.4.After comprehensively considering the conclusion of dynamic characteristic optimization,the design index of dynamic and static parameters and the existing process conditions,the 100V-class shielded gate trench MOSFET is designed.The device has completed various dynamic and static parameter tests and met the design specifications.In the inductive load switch test and the body diode reverse recovery test,the drain-source voltage oscillation only reaches 6.75%and 17.14%of the power supply voltage.The test results verify the practicability of the optimization conclusion of dynamic characteristics.