Trench depletion MOSFET

DETAILED DESCRIPTION The present invention is a trench power MOSFET with a unique structure which overcomes the above-noted deficiencies of the prior art.
Advantageously, the present invention, like the trench power MOSFET of FIG.
2, does not have a P base region and thus has no P-N junction.
Thus, the trench power MOSFET of the present invention is formed in a wafer of semiconductor material having first and second (i.
e.
upper and lower) opposing semiconductor surfaces, the wafer of semiconductor material including a relatively lightly doped region of a first conductivity type, preferably N.
sup.
-, a plurality of spaced narrow trenches perpendicularly formed in the wafer and extending from the upper surface of the wafer, at least a portion of the N.
sup.
- region being disposed between the trenches from the upper semiconductor surface.
Polysilicon gates are disposed in the trenches and spaced from the intervening portion of the N.
sup.
- region by a layer of gate insulation material.
A first relatively highly doped region of the first conductivity type, i.
e.
N.
sup.
+, is disposed between and adjacent to the upper semiconductor surface and the N.
sup.
- region.
The present invention is an improvement over the prior art device of FIG.
2, however, by the inclusion, in a first embodiment, of a P.
sup.
+ region formed in the wafer and extending from the upper surface of the wafer at a position adjacent to and at least partially co-extensive with the upper N.
sup.
+ region, i.
e.
the source region.
On application of a negative gate voltage to turn the device off, the added P.
sup.
+ region forms a drain for holes generated in the N.
sup.
- region.
Thus, as soon as the holes are formed, they are swept off towards the P.
sup.
+ region by the electric field, via a trench p-channel MOSFET.
This effect is hereinafter termed "deep-depletion.
" The deep-depletion very efficiently pinches off the N.
sup.
- region between the trench MOS gates, forming a potential barrier to the flow of electrons and greatly improving the forward blocking capability of the device