Optimization of SiC UMOSFET Structure for Improvement of Breakdown Voltage and ON-Resistance

This paper proposes an optimized structure of 4H-SiC U-shaped accumulation-mode MOSFET (U-ACCUFET), which exhibits lower on-resistance and higher breakdown voltage. In this structure, an n-doped region is added underneath the gate trench, which covers the p<sup>+</sup> shielding region. The new appended section spreads out the electrons to the bottom of the p<sup>+</sup> shielding region and conducts the electrons in the downward direction. Output on-state characteristic curves (<inline-formula> <tex-math notation="LaTeX">${I}_{\mathrm {DS}}$ </tex-math></inline-formula>–<inline-formula> <tex-math notation="LaTeX">${V}_{\textsf {DS}}$ </tex-math></inline-formula>), on-resistance, transfer characteristic curves (<inline-formula> <tex-math notation="LaTeX">${I}_{\textsf {DS}}$ </tex-math></inline-formula>–<inline-formula> <tex-math notation="LaTeX">${V}_{\textsf {GS}}$ </tex-math></inline-formula>), threshold voltage (<inline-formula> <tex-math notation="LaTeX">${V}_{t}$ </tex-math></inline-formula>), subthreshold slope, and off-state characteristics of the optimized structure are observed. The proposed device shows on-resistance of 1.55 <inline-formula> <tex-math notation="LaTeX">$\text{m}\Omega ~\cdot $ </tex-math></inline-formula> cm<sup>2</sup> at <inline-formula> <tex-math notation="LaTeX">${V}_{\textsf {GS}}= \textsf {16}$ </tex-math></inline-formula> V and <inline-formula> <tex-math notation="LaTeX">${V}_{\textsf {DS}}= \textsf {1}$ </tex-math></inline-formula> V and breakdown voltage of 2624 V at <inline-formula> <tex-math notation="LaTeX">${V}_{\textsf {GS}}= \textsf {0}$ </tex-math></inline-formula> V. The simulation results indicate a superior performance of the optimized U-ACCUFET structure as the on-resistance reduces by 6% and breakdown voltage increases by 7.2% as compared with that of the conventional one. Also, the figure of merit <inline-formula> <tex-math notation="LaTeX">${V}_{\textsf {BR}}^{\textsf {2}}/{R}_{ \mathrm{\scriptscriptstyle ON}}$ </tex-math></inline-formula> is improved by 21.6%.

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