A semi-superjunction MOSFET with P-type Bottom Assist Layer

•The P-BAL is introduced in the n-BAL.•The BV of the proposed MOSFET is improved 25% higher than the conventional.•The trade-off between the BV and Ron,sp is enhanced.

A new Semi-Superjunction Vertical Double-diffusion MOSFET (Semi-SJ MOSFET) with P-type Bottom Assist Layer (P-BAL) is proposed. The P-BAL is introduced upon the N-Stop substrate and embedded in the n-BAL, on the one hand, another reverse biasing PN junction JP-BAL/N-Stop at the bottom substrate is formed, which helps to deplete the n-BAL along the longitudinal direction and changes the shapes of the electric field distribution. On the other hand, another Semi-SJ structure is formed by the P-BAL and n-BAL, the transverse electric field in n-BAL part is enhanced, and this indicates that the trade-off between breakdown voltage (BV) and on-state resistance (Ron,sp) has been optimized due to the improvement of BV. As results show, in the proposed MOSFET, the BV (i.e., 1097 V) is improved 25% higher than that of the conventional Semi-SJ structure (i.e., 877 V) and the proposed does negligible disadvantage to the Ron,sp (i.e., the proposed with a Ron,sp of 59 mΩ cm2 and the conventional MOSFET with a Ron,sp of 56 mΩ cm2).