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 has 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 us. In this paper, we compare characteristics of ACCUFETs fabricated from 6H-SiC and 4H-SiC polytypes. A room temperature specific on-resistance (R-on,R-sp) of 18 m Omega-cm(2) was measured on the best 6H-SiC device (designed for a breakdown voltage of 1500V) at a logic-level gate drive voltage of only 5V, which was in excellent agreement with 15 m Omega-cm(2) obtained in simulations. The R-on,R-sp exhibited a positive temperature coefficient. In contrast, the room temperature R-on,R-sp for the best 4H-SiC reduced rapidly with increase in temperature to 128 m Omega-cm(2) at 450 K. At room temperature, the unterminated 6H-SiC and 4H-SiC devices had a breakdown voltage (BV) of 350V and 450 V, respectively, with a leakage current of < 100 mu A. However, a breakdown voltage of 1240V is obtainable from the epitaxial material on using an Ar implant (amorphization) edge termination.