Advanced Floating Island and Thick Bottom Oxide Trench Gate MOSFET (FITMOS) with reduced RonA during AC operation by passive hole gate and improved BVdss RonA trade-off by elliptical floating island

A MOSFET structure called a FITMOS (floating island and thick bottom oxide trench gate MOSFET) has been successfully developed that exhibits record-low loss in the 60 V breakdown voltage (BVdss) range. The device has a body diode with superior reverse recovery characteristics and exhibits an extremely small value for RonQgd. The distinctive features of this device are the use of floating P islands formed by self-alignment and trench gates with a thick oxide layer at the bottom. The following improvements achieved progress in the characteristic of FITMOS. At the time of AC operation, the charges in the floating P islands which are a feature of the floating type device become greater, increasing the on-resistance (Ron) due to the JFET effect. This issue was solved by forming passive hole gates in the end walls of the trenches. The Ron under AC operation is equivalent to the Ron under DC operation. The trade-off of BVdss and Ron has been improved by making the form of the floating island into an elliptical form. A BVdss of 83 V and specific on-resistance (RonA) of 36 mOmegamm² were obtained.