We report the experimental results detailed about the n-buffer layer (n-BAL: n-Bottom Assist Layer) of 600V-class Semi-SJ MOSFET, and discuss about the design optimization by comparing the trade-off characteristics between the specific on-resistance (RonA) and the breakdown voltage (VB), the avalanche capability and the body diode characteristic for the first time. As design parameters, the thickness ratio TBAL-ratio and the doping concentration NBAL were varied in this work. As a result, the VB=750V, the RonA= 24.6m驴cm2, the maximum avalanche current density JAP=292A/cm2 (IAP=7.6A, EAS=1.25J/cm2), and softness factor=0.277 were obtained with the structure of TBAL-ratio=27% and NBAL=1.0脳l015cm-3. The demonstration results showed that NPT (Non Punch Through)-type design (with high TBAL-ratio and high NBAL) realized the larger avalanche capability and the softer reverse recovery characteristic compared with PT (Punch Through)-type design.
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