Carrier trapping hysteresis in MOS transistors

Measurements have been made of the hysteresis in the drain current (or equivalent gate voltage) of a number of commercial MOS transistors. The hysteresis was obtained after applying a negative voltage on the gate electrode. The hysteresis is attributed to trapping of charge carriers on oxide near the silicon oxide interface. A gate voltage hysteresis of the order of 0.01 to 0.2 V has been obtained depending on the transistor and kind of measurement. The traps studied follow a time constant dispersion of the form dN = (N0/τ) dτ, where dN is the density of traps with time constants between τ and τ + dτ and N0 is a normalization constant. It is shown that this time-constant dispersion is compatible with a simple tunneling model for the charge trapping and also with the low-frequency noise spectrum obtained from MOS transistors.