Silicon Switches with Ultra-low Conduction Loss for Low Frequency Switching Applications

Shielded-gate UMOSFET is one of the most popular commercially available silicon switch due to its high frequency switching capability for a given rated voltage. However, in this paper, we establish that an extended-gate UMOSFET is a better alternative for low frequency switching applications, $\lt 20 \mathrm{kHz}$. Well calibrated TCAD simulations predict that extended-gate UMOSFET can offer up to $34 \%$ lesser specific on resistance compared to shielded-gate UMOSFET at 60 V rating and using a graded doped (GD) epitaxial wafer. Additionally, we investigate the role of mesa width and oxide thickness in deciding the breakdown voltage in order to develop design insights. It is found that there exist an optimum oxide thickness below which the device breaks down prematurely due to electric field peaking at trench corner and above which the superjunction effect is not strong enough to deplete mesa region laterally resulting in early breakdown at the p-base / n-drift junction. This study should motivate the use of customized extended-gate GD-UMOSFET for low frequency switching applications rather than a generic switch optimized for best switching performance.