Research On Reverse Recovery Robustness Of Multi-cell Bootstrap Diode For GaN-FET Driver Chip

The Ga N device has a series of excellent characteristics,such as high operating frequency,high output power,low switching loss and so on,so it has become more and more widely used in recent years,and the Ga N drive circuit has become one of the current research hotspots.However,the bootstrap diode in Ga N driver ICs is prone to failure in high-frequency applications,which will damage the whole chip.Therefore,optimizing reverse recovery robustness of the bootstrap diode is of great significance to improve the reliability of Ga N gate driver ICs.Based on the reverse recovery robustness of the multi-cell bootstrap diode,it is found that during the reverse recovery period,the holes in the drift region of the cell near the terminal can be extracted by anode and terminal grounding ring at the same time,so the extraction rate is faster;however,the holes in the drift region of the central cell are only extracted by anode,and the extraction rate is slow.Because of the difference of the extraction rate of holes among the cells,the dynamic avalanche easily occurs in the central cell region with slow extraction rate and large number of carriers,and the reverse recovery robustness of the multi-cell bootstrap diode is much lower than that of the single-cell one.Based on the above analysis,improved schemes of adding P+ field limiting ring and optimizing cell size are proposed in this thesis.The addition of P+ field limiting ring suppresses the peak electric field outside the central cell electrode and optimizing cell size improves the reverse recovery nonuniformity.Both schemes significantly improve the reverse recovery robustness of the multi-cell diode.The simulation results show that the forward conduction voltage drop of the optimized structure is 0.84V(the forward current is 100 m A)and the breakdown voltage is 152 V.Under the conditions of100 V operating voltage and 400 m A conduction current,the reverse recovery time is not more than40 ns and the change rate of reverse recovery current di/dt is more than 700A/?s(di/dt<133A/?s in conventional structure),and the device can still operate normally.The reverse recovery robustness of the optimized multi-cell diode is significantly improved without sacrificing the forward current capability and breakdown voltage.