The effect of a floating substrate on the operation of silicon-on-sapphire transistors

It was observed that during operation of SOS counter circuits, the propagation delay between stages was a function of the operating frequency. Further analysis proved the change in propagation delay to be associated with the change in the magnitude of a transient drain current. The origin of the transient current was found to lie in properties of the floating substrate. This paper discusses these properties and their effect on transistor operation, including threshold voltage, drain current, rise and fall times, and propagation delay. The effect of states at the Si-sapphire interface is also described.