100-V Class Two-step-oxide Field-Plate Trench MOSFET to Achieve Optimum RESURF Effect and Ultralow On-resistance

We propose a 100-V class two-step-oxide Field-Plate MOSFET (2-step FP-MOSFET), which is formed by two steps of thick-oxide to simplify the structure and fabrication process. By optimizing design parameters, we reveal the 2-step FP-MOSFET can achieve sufficient RESURF (Reduced Surface Field) effect and an ultralow specific on-resistance ( RONA). Measurement results showed breakdown voltage of 109.9 V and the RONA of 27.7 mohm·mm² with good process controllability. Moreover, as figure-of-merit of the 2-step FP-MOSFET, RON·Qg and RON·Qsw were reduced by 27.1% and 4.7%, respectively, compared with conventional one. Power loss estimation is also discussed by simple calculation.

I. Introduction

Field-plate trench MOSFETs (FP-MOSFETs) have been continuously developed for high efficiency and low energy consumption power electronics [1]–[9]. In particular, 100-V class MOSFETs are expected to be applied to 48-V input power converters and 48-V battery automobile systems. In the FP-MOSFET, vertical field plates inside trench have RESURF (Reduced Surface Field) effect in mesa region with high impurity concentration, so that tradeoff between breakdown voltage () and specific on-resistance () is drastically improved. We have reported that multiple stepped oxide (MSO) FP-MOSFET can achieve an ultralow [10]. It was close to an ideal gradient field-plate structure in [11], however, in order to realize the structure, many additional process steps such as deposition and etching were needed.