Trench depth optimization for energy efficient discrete power trench MOSFETs

Power losses are investigated in trench MOSFETs as functions of trench depth and switching frequency. MOSFETs with different trench depths are fabricated and characterized. Measurements show that gate charge and capacitance increases with trench depth thereby increasing switching losses. However, conduction losses reduce with increasing trench depth because of higher gate-modulated accumulation charge at the drain. Since switching losses increase with frequency, the trade-off between the conduction and switching losses for different trench depths will be determined by the switching frequency. In conclusion, deep-trench MOSFETs outperform shallow-trench MOSFETs at low frequencies and become outperformed by the latter at high frequencies.