Behavior of Split-Gate Trench MOSFETs in Critical Conditions Caused by Distributed Effects

The split-gate trench (SGT) MOSFET is a vertical power device having a separate field plate (FP) inside a deep trench. This design increases the breakdown voltage (BV) via the reduced surface field (RESURF) effect. However, during switching operations via fast transients, voltage fluctuations in various parts of the device can appear. These are due to distributed effects and can lead to premature breakdown, current crowding, and, in the worst case, device failure. In this work, an on-wafer transmission line pulse (TLP) setup together with technology computer-aided design (TCAD) simulations are employed to analyze the behavior of SGT MOSFETs in critical conditions caused by distributed effects. These typically occur for a higher FP potential, a gate-source voltage near the threshold voltage, or a combination of both. From this analysis, a compact model has been developed, which is used in distributed SPICE simulations. The results indicate a great impact of the gate and FP potential variations on the BV. Moreover, they show how both the avalanche and channel current can affect the charge balance inside the device. Finally, the simulations show that a good model for the impact of the FP voltage on BV is necessary for an accurate prediction of the device behavior and layout optimization.