Quasisaturation Effect and Optimization for 4H-SiC Trench MOSFET With P plus Shielding Region

The 4H-SiC trench metal-oxide semiconductor field-effect transistor (MOSFET) with the grounded p+ shielding region is one of the commercial devices with superior gate oxide reliability. However, the introduced JFET region seriously increases the influence of quasisaturation (QS) on device electrical performances, resulting in the poor output and transfer characteristics. In order to investigate the mechanism of QS effect, the output characteristic is physically analyzed by monitoring the variations of the electric field, the electron concentration, the electron velocity, and the depletion layer inside the cell structure. It is demonstrated that the channel electrons are injected into the JFET current path from the channel region by a forward bias to the channel and JFET junction at QS state. Moreover, based on the Lombardi CVT model, the influence of QS effect on devices with different channel electron mobilities is first studied. An improved SiC trench MOSFET with two-level doped current spreading layers is proposed to decrease the JFET resistance and suppress the QS effect. The QS current and the peak transconductance are improved by 42% and 23%, respectively. The specific ON-state resistance is decreased by 10% and the figure of merit is improved by 7%.