Novel SiC MOSFETs with merged schottky or MOS-channel diode for enhanced performance based on numerical simulations

Abstract

Silicon carbide (SiC) metal-oxide-semiconductor field-effect transistors (MOSFETs) are widely used in today’s power electronics systems. However, the potential of SiC MOSFETs has not been explored extensively. The performance of SiC MOSFETs can still be improved significantly. Therefore, various novel structures of SiC MOSFETs are proposed and investigated by TCAD simulations comprehensively in this research. Firstly, SiC MOSFET with centrally-implanted P++ region (CIP-MOS) and SiC MOSFET with centrally-implanted P++ and P+ regions (CIPP-MOS) are proposed. The centrally-implanted P++ and P+ regions in the proposed MOSFETs can help reduce the electric field in the gate oxide under high off-state voltage. The split-gates in the devices can help reduce their gate-to-drain capacitances (CGD), thus decreasing their switching energy losses. The integrated Schottky barrier diodes in the devices can decrease their forward voltages (VF) and improve their reverse recovery performances. Secondly, a novel SiC trench MOSFET with built-in MOS-channel diode is proposed. Although the on-resistance (RON) of the proposed device increases by 7.6 % due to lower channel density when compared with the conventional SiC trench MOSFET, the lower CGD of the device helps lower its switching energy loss. Moreover, the built-in MOS-channel diode helps decrease the VF of the device and improve its reverse recovery performance. Thirdly, a novel SiC trench super-junction MOSFET with built-in MOS-channel diode is proposed. The RON of the proposed device increases by 15.6 % also due to lower channel density when compared with the conventional SiC trench super-junction MOSFET. The switching energy loss and VF of the device are reduced due to lower CGD and the MOS-channel diode, respectively。 Fourthly, a novel SiC trench MOSFET with high-k pillar and integrated MOS-channel diode (SiC THK-MCD MOSFET) is proposed. Despite the higher RON of the proposed device than the conventional SiC THK MOSFET, VF and reverse recovery performance are improved due to lower potential barrier for electron injection and lower minority-carrier concentration respectively achieved by the MOS-channel diode. Lower switching energy loss is also obtained due to lower CGD. Fifthly, a novel SiC shield gate trench MOSFET with high-k pillar (SiC HK-SGTMOS) and a novel SiC shield gate trench MOSFET with high-k pillar and low-k dielectric layer between the gate and the shield gate (SiC HLK-SGTMOS) are proposed. Lower CGD and CGS are achieved by the shield gate and the low-k dielectric layer of the two devices, respectively, thus decreasing their switching energy losses significantly. Sixthly, a novel SiC high-k MOSFET with integrated Schottky barrier diode is proposed. The spilt-gate of the device helps reduce its CGD, thus reducing its switching power loss. The VF and reverse recovery performance of the device are improved due to lower potential barrier for electron injection and lower minority-carrier concentration respectively achieved by the Schottky barrier diode. Finally, the effects of Coulomb and surface-roughness scatterings on SiC MOSFET are investigated by simulations and experiments. After fitting the experimental results with the simulated results, both scatterings are demonstrated to have significant impact on the carrier mobility of the device.