AGING OF METAL-SEMICONDUCTOR FIELD-EFFECT TRANSISTORS

The ageing effect in silicon metal-semiconductor field effect transist ors is studied by taking into account the reaction of the gate contact with the native SiO2 layer on the silicon surface. Specifically, the effect of ageing on the threshold voltage and drain characteristics ha s been studied. It is shown that the change in the threshold voltage w ith time is quite significant until it becomes nearly constant after a considerably long time. The drain current-voltage characteristics of the device also show appreciable drift with time. It is also shown tha t, depending on the values of the interface parameters and doping, the device may make a transition from the normally on to a normally off s tate after prolong ageing. An expression for the critical time require d to make such a transition in silicon devices is derived.