Optimization of MNOS device performance

The MNOS (metal-nitride-oxide-semiconductor) memory transistor is similar in geometry and fabrication technique to standard MOS (metal-oxide-semiconductor) devices, except for the gate insulator, which is a two layer structure of silicon dioxide nearest the silicon and silicon nitride on top of the silicon dioxide. Donor-type defect states, or traps, exist at or near the interface between these two insulators, and the states may be charged and discharged by the application of electric fields to the insulators. The amount of charge in the traps influences the surface potential of the silicon, and can therefore be used to alter the threshold voltage of a transistor fabricated with this double insulator structure.