Comparison of 6H-SiC and 4H-SiC high voltage planar ACCUFETs

SiC switches are extremely promising for high power applications, such as UPS and motor control, because of extremely low power losses as compared to Si devices. Although very low diffusion coefficients in SiC have motivated the fabrication of UMOSFETs, the performance of these devices has been limited by premature oxide breakdown and low inversion layer mobility. A novel planar vertical MOSFET structure (called ACCUFET), which eliminates both these problems, has been demonstrated by the authors. In this paper, we compare characteristics of ACCUFETs fabricated from 6H-SiC and 4H-SiC polytypes. A room temperature specific on-resistance (R_on,sp) of 18 mΩ-cm² was measured on the best 6H-SiC device (designed for a breakdown voltage of 1500 V) at a logic-level gate drive voltage of only 5 V, which was in excellent agreement with 15 mΩ-cm² obtained in simulations. The R^on,sp exhibited a positive temperature coefficient. In contrast, the room temperature R_on,sp for the best 4H-SiC reduced rapidly with increase in temperature to 128 mΩ-cm² at 450 K. At room temperature, the unterminated 6H-SiC and 4H-SiC devices had breakdown voltages (BV) of 350 V and 450 V, respectively, with a leakage current of <100 μA. However, a breakdown voltage of 1240 V is obtainable from the epitaxial material on using an Ar implant (amorphization) edge termination