Ultralow Specific on-Resistance Trench MOSFET with a U-Shaped Extended Gate**Supported by the National Natural Science Foundation of China under Grant No 61376079, and the Fundamental Research Funds for the Central Universities under Grant No ZYGX2013J043.

Abstract

An ultralow specific on-resistance (Ron,sp) trench metal-oxide-semiconductor field effect transistor (MOSFET) with an improved off-state breakdown voltage (BV) is proposed. It features a U-shaped gate around the drift region and an oxide trench inserted in the drift region (UG MOSFET). In the on-state, the U-shaped gate induces a high density electron accumulation layer along its sidewall, which provides a low-resistance current path from the source to the drain, realizing an ultralow Ron,sp. The value of Ron,sp is almost independent of the drift doping concentration, and thus the UG MOSFET breaks through the contradiction relationship between Ron,sp and the off-state BV. Moreover, the oxide trench folds the drift region, enabling the UG MOSFET to support a high BV with a shortened cell pitch. The UG MOSFET achieves an Ron,sp of 2 mΩ·cm2 and an improved BV of 216 V, superior to the best existing state-of-the-art transistors at the same BV level.