Characterization of silicon-on-sapphire IGFET transistors

Under dynamic operation conditions, the potential of the floating substrate in a silicon-on-sapphire (SOS) device is primarily controlled by the capacitive coupling of the substrate to other device terminals. However, a key parameter that plays a major role in defining that potential during switching is the avalanche multiplication current produced by the channel current carriers in the surface space charge region adjacent to the drain. A closed form expression is derived for the avalanche current, enabling the development of a nonlinear equivalent circuit model of the device. Comparison of measurements with device terminal characteristics, as well as the switching behavior of the device, shows good agreement.