Improvement of Qrr–IDSS and dynamic avalanche of field-plate MOSFET by local lifetime control on the cathode side

Reducing the reverse recovery charge (Qrr) is effective for reducing switching loss in field plate (FP)-MOSFETs. A lifetime killer is utilized to reduce Qrr while increasing the leakage current in the off-state. Device simulation shows that a local lifetime killer on the cathode side successfully improves the trade-off between Qrr and IDSS in comparison with that of a uniform lifetime killer. A known issue of cathode lifetime killers is overshoot voltage by hard recovery. However, the overshoot voltage of FP-MOSFET decreases with a cathode lifetime killer owing to an internal snubber, which is a feature of FP-MOSFETs. An internal snubber with a large series resistance causes a dynamic avalanche by both the increase of FP potential and excess carriers in high-speed operation. The cathode lifetime killer also improves dynamic avalanche by excess carriers. Consequently, the cathode lifetime killer is preferable for high-speed FP-MOSFETs because the Qrr–IDSS trade-off and the trade-off between dynamic avalanche and IDSS are effectively improved.