Clamping Capability of Parasitic p-n Diode in SBD-Embedded SiC MOSFETs
T. Ohashi, Hiroshi Kono, Souzou Kanie, Takahiro Ogata, Kenya Sano, Hideki Hayakawa, Shunsuke Asaba, Shigeto Fukatsu, Ryosuke Iijima
Abstract
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 ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${J}_{\text{umax}}$ </tex-math></inline-formula> ) decreases with increasing temperature. Therefore, further improvement of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${J}_{\text{umax}}$ </tex-math></inline-formula> and understanding the mechanism of the temperature dependence of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${J}_{\text{umax}}$ </tex-math></inline-formula> are urgent issues. We have developed an equivalent circuit model of SBD-embedded SiC MOSFETs and derived an analytical formula of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${J}_{\text{umax}}$ </tex-math></inline-formula> . Based on the derived analytical formula of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${J}_{\text{umax}}$ </tex-math></inline-formula> , we have proposed guidelines for improving <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${J}_{\text{umax}}$ </tex-math></inline-formula> . Then, utilizing the guidelines, we have tried to improve <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${J}_{\text{umax}}$ </tex-math></inline-formula> experimentally. As a result, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${J}_{\text{umax}}$ </tex-math></inline-formula> of 3.3 kV SBD-embedded SiC MOSFETs has been improved by 3.8 times. In addition, the mechanisms by which <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${J}_{\text{umax}}$ </tex-math></inline-formula> decreases in high blocking voltage devices and at high temperature have been investigated. We have found that the blocking voltage dependence of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${J}_{\text{umax}}$ </tex-math></inline-formula> 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 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${J}_{\text{umax}}$ </tex-math></inline-formula> is not necessarily a problem because the rated current density also decreases in high blocking voltage devices. From the partial differentiation of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${J}_{\text{umax}}$ </tex-math></inline-formula> ’s analytical formula with respect to temperature, it has been clarified that the decrease in <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${J}_{\text{umax}}$ </tex-math></inline-formula> is mainly due to the increase in the spread resistance and the JBS resistance.