Simple analytical models for the temperature dependent threshold behavior of depletion-mode devices

Threshold voltage shifts in ion-implanted depletion-mode MOSFET's depart substantially from the usual dose proportional shift of enhancement-mode devices. Analytic expressions for the relationship between threshold voltage shift and implanted donor dose and position are extended to include impurity freezeout at low temperatures, and a simple model for the observed low substrate sensitivity at low temperature is presented. Criteria to avoid parasitic subthreshold conduction in depletion-mode devices are also established using the threshold shift formulation.