Increase of gate capacitance in DMOST

The gate capacitance of an n-channel DMOST at nonzero drain current biasing exceeds that of a similar conventional MOST and may even exceed the gate oxide capacitance. This effect is due to the behavior of mobile electrons in the device. The fundamental operation of the DMOST is understood through the use of a two-dimensional computer analysis. Based on this insight, the increase of the gate capacitance is clarified in terms of the electron velocity between the source and the drain. Gate capacitance measurements are carried out on experimental DMOST\´s, which are made on a p^-background as well as on an n^-epitaxial layer. The measured curves qualitatively confirm the theory on the increase of the gate capacitance in its dependence on the background of the DMOST and the applied dc voltages.