Nonuniform displacement of MOSFET channel pinchoff

The effects of fixed, positive oxide charge under the gate on the characteristics of MOSFET devices are well known. But the combined effects of the oxide charge in the field and of the edge contour and impurity profile on the device characteristics have not been as extensively investigated in the past. In this paper we address this problem and show results which give a new insight in the performance of MOSFET devices. With the help of two-and three-dimensional numerical solutions of Poisson´s equation, it was found that this oxide charge lowers the threshold potential resulting in an increase in conductivity towards the two edges of the channel along the width direction. As a consequence, the geometric channel pinchoff locus shifts towards the drain as the channel edge is approached. This is in contrast to the conventional assumption of the pinchoff locus being in parallel to the drain.