Clamping Capability of Parasitic p-n Diode in SBD-Embedded SiC MOSFETs

Schottky barrier diode (SBD)-embedded SiC MOSFETs can clamp the parasitic p-n diode that causes a lack of long-term stability and thus realize high reliability. However, the maximum current density at which the parasitic p-n diode does not operate (J(umax)) decreases with increasing temperature. Therefore, further improvement of J(umax) and understanding the mechanism of the temperature dependence of J(umax) are urgent issues. We have developed an equivalent circuit model of SBD-embedded SiC MOSFETs and derived an analytical formula of J(umax). Based on the derived analytical formula of J(umax), we have proposed guidelines for improving J(umax). Then, utilizing the guidelines, we have tried to improve J(umax) experimentally. As a result, J(umax) of 3.3 kV SBD-embedded SiC MOSFETs has been improved by 3.8 times. In addition, the mechanisms by which A max decreases in high blocking voltage devices and at high temperature have been investigated. We have found that the blocking voltage dependence of J(umax) is caused by the change in the current distribution due to the difference in the drift resistance. On the other hand, it has also been confirmed that the decrease in J(umax) is not necessarily a problem because the rated current density also decreases in high blocking voltage devices. From the partial differentiation of J(umax)'s analytical formula with respect to temperature, it has been clarified that the decrease in J(umax) is mainly due to the increase in the spread resistance and the JBS resistance.