Trench-gated power MOSFET with protective diode having adjustabl

Active solid-state devices (e.g. – transistors – solid-state diode – Field effect device – Having insulated electrode

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Details

257331, 257342, 257328, 257409, H01L 2978, H01L 2949, H01L 29866

Patent

active

059988371

ABSTRACT:
A power MOSFET includes a trenched gate which defines a plurality of MOSFET cells. A protective diffusion is created, preferably in an inactive cell, so as to form a PN junction diode that is connected in parallel with the channel region in each of the MOSFET cells. The diode can be designed to have a breakdown voltage which limits the strength of the electric field across the gate oxide layer. Several techniques can be used to adjust the breakdown voltage of the PN diode and to insure that breakdown occurs away from the sidewall of the trench, where it could cause impact ionization which could damage the gate oxide layer. According to one technique, a region of the epitaxial layer beneath the PN junction can be doped more heavily than the background level in the epitaxial layer to reduce the breakdown voltage of the PN junction diode. Also the radius of curvature of the PN junction and the separation between the protective diffusion and the heavily doped substrate can be used for this purpose. In other embodiments a zener diode is formed in the diode cell, located either at the surface of the epitaxial layer or buried in the diode cell.

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Masakatsu Hoshi, et al., "A DMOSFET Having A Cell Array Field Ring for Improving Avalanche Capability", May 18, 1993, IEEE Proceedings of the 5th International Symposium on Power Semiconductor Devices and IC's (ISPSD), Monterey, May 18-20, 1993, pp. 140-145, XP000380145.

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