An approach to analytical modeling of snapback in SOI devices

The snapback effect in N channel SOI devices in which the drain to source breakdown voltage is less than the drain to body breakdown voltage is addressed. The purpose is to present an approach to snapback modeling based on nonlinear feedback mechanisms between impact ionization current, the body to source forward bias, the threshold voltage, and the drain current supplying carriers to enhance impact ionization. NMOS SOI devices with the body either tied to the source of floating are analyzed. As the gate voltage first increases and then decreases, the device first operates in the subthreshold region, then jumps abruptly to the strong inversion regime and finally jumps back to the subthreshold region of operation. The model results in transcendental feedback expressions. It is possible to obtain closed-form expressions for the device currents and voltages at the jump points