Akira Kuroyanagi

Floating island and thick bottom oxide trench gate MOSFET (FITMOS) - a 60V ultra low on-resistance novel MOSFET with superior internal body diode

A MOSFET structure named FITMOS has been successfully developed and exhibits record-low loss in the 60 volt breakdown voltage range. The device has a body diode with superior reverse recovery characteristics and exhibits an extremely small value for RonQgd. The distinctive feature of this device is the use of floating islands formed by self-alignment and trench gates with a thick oxide layer on the bottom. This structure can also be used for the terminal portion of the device, so the increase in the number of fabrication process steps is less than 5%. Moreover, the rate of non-defective-gates in 3-by-4-mm rectangular devices on an 8-inch wafer is at least 98%.

High Performance and Reliability Trench Gate Power MOSFET With Partially Thick Gate Oxide Film Structure (PTOx-TMOS)

We have developed a novel trench-gate MOSFET (TMOS) with partially thick gate oxide film structure (PTOx) performing lower dissipation and higher reliability. The PTOx structure consists of thick oxide around trench top (Ttt), thin oxide at trench side (Tts), and thick oxide at trench bottom (Ttb), and is formed by our original simple process characterized by remaining SiN film in trench side oxide. We found out the optimum thickness in Ttb in terms of maximum drain breakdown voltage (Vdss), and the thickness of Ttb is 2 to 3 times larger than that of Tts. For 250V device, optimum thickness of Ttb is 150nm, while Tts is 60nm. We clarified Ron*Qgd reductions of PTOx-TMOS for wide blocking voltage range up to 250V for the first time. Estimated Ron*Qgd reductions compared with conventional devices are 32% at 60V, 28% at 100V, and 25% at 250V. Fabricated PTOx-TMOS of 100V and 250V denote high performance corresponding with estimation, and stress reduction in those gate oxides against high electric field is successfully achieved and promising high reliability