Miller-Capacitance Analysis of High-Voltage MOSFETs and Optimization Strategies for LowPower Dissipation

High voltage MOSFETs are widely used for bias ranges of a few dozens of volts to a few hundred of volts. The trench-type MOSFET is one of the key devices for realizing this wide range applications. However, the device characteristics are not yet well understood, especially, the Miller-capacitance variation for different device structures is still mysterious. Here we show, that the capacitance variation is very much dependent on the applied device structure. An observed capacitance increase as a function of V
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, contrary to the conventional decreasing trend, is due to the large induced field within the highly resistive drift region. A narrow width of the drift region in a super-junction structure will easily become fully depleted, due to the junction between drift and pillar region of the substrate, which causes a fully depleted condition. This full-depletion situation induces a high field within the drift region, resulting in a potential increase even at the gate oxide.