Composite channel field effect transistor and method of fabrication

DETAILED DESCRIPTION Accordingly, it is an object of the present invention to provide an improved composite channel field effect transistor, and method of fabrication thereof, which exhibits high density characteristics and yields high performance, with less sensitivity to threshold voltage shifts caused by the hot electron effect when the transistor is operated at source to drain voltage levels in the order of 3 to 4 volts or above.
This object and other features of the invention are attained with an insulated gate field effect transistor which is provided with a channel construction which comprises a composite of three regions of the same conductivity type material, but with one region having a different doping density than the other two regions and the former region separating the latter two regions.
In operation the composite channel device functions as a short channel device in conventional operation since the end regions are depleted and the effective length is reduced.
When operated at relatively high drain to source voltages hot electrons still penetrate into the silicon dioxide layer near the drain electrode.
However, any shifting of the threshold voltage at the end portions of the channel does not effect the overall device operation unless the voltage shift is of such a high magnitude that it exceeds the threshold voltage of the center portion of the device.
Accordingly, the device provides satisfactory characteristics while exhibiting significant resistance to threshold voltage shift.