The Mechanisms of Small Instabilities in Irradiated MOS Transistors

When a metal-oxide semiconductor (MOS) device is irradiated, charge builds up in the oxide and new interface states are also created. The charge and discharge of "slow interface states" cause the flat-band and threshold voltage of a device held under bias to drift with time. The effect is distinctfrom ionic instabilities. Even small radiation-induced drift effects may be of importance in precision devices such as MOS comparators and regulators. Some recent data arising from experiments on precision MOS devices, - mainly using gamma irradiation are presented and methods of minimising radiation-induced slow drift effects are discussed.