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 (
${J}_{\text{umax}}$
) decreases with increasing temperature. Therefore, further improvement of
${J}_{\text{umax}}$
and understanding the mechanism of the temperature dependence of
${J}_{\text{umax}}$
are urgent issues. We have developed an equivalent circuit model of SBD-embedded SiC MOSFETs and derived an analytical formula of
${J}_{\text{umax}}$
. Based on the derived analytical formula of
${J}_{\text{umax}}$
, we have proposed guidelines for improving
${J}_{\text{umax}}$
. Then, utilizing the guidelines, we have tried to improve
${J}_{\text{umax}}$
experimentally. As a result,
${J}_{\text{umax}}$
of 3.3 kV SBD-embedded SiC MOSFETs has been improved by 3.8 times. In addition, the mechanisms by which
${J}_{\text{umax}}$
decreases in high blocking voltage devices and at high temperature have been investigated. We have found that the blocking voltage dependence of
${J}_{\text{umax}}$
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
${J}_{\text{umax}}$
is not necessarily a problem because the rated current density also decreases in high blocking voltage devices. From the partial differentiation of
${J}_{\text{umax}}$
’s analytical formula with respect to temperature, it has been clarified that the decrease in
${J}_{\text{umax}}$
is mainly due to the increase in the spread resistance and the JBS resistance.