Threshold Voltage Adjustment on 4H-SiC MOSFETs Using P-Doped Polysilicon as a Gate Material

Abstract

To scale digital circuits, symmetric threshold voltages (Vth) for n-type transistors (NMOS) and p-type transistors (PMOS) are important. One step towards this in silicon carbide (SiC) is selecting a p-doped polysilicon (pPolySi). This implementation has been shown in this work with Vth being evaluated by five different methods. Furthermore, operating temperatures up to 500 °C and their impact on Vth were investigated. It has been successfully demonstrated that elevated temperature shifts Vth of both transistor types towards 0 V, whereas changing the gate electrode from n-doped PolySi (nPolySi) to pPolySi shifts Vth of both transistor types to more positive values. Both effects are complementary for the PMOS, reaching Vth below 4 V.