Effects of high-field stressing on the channel frequency-response of MOSFETs

The frequency response of the MOSFET inverted channel is analyzed by a transmission-line model. In this model, the interface traps are included and the minority carriers are assumed to follow the surface-potential variation. The channel frequency-response is characterized by two time constants (τ_l and τ_GC). The conductance G_l and capacitance C₁ calculated from the minority-carrier current in the channel is used to determine τ_I and τ_GC from a frequency scan. Theoretical C₁(V) and G₁(V) curves are calculated and are in good agreement with experiments. The effect of high electrical field stressing is shown to increase both τ_I and τ_GC and thereby enlarge the frequency dispersion of the MOSFET admittances in inversion. The degradation in the channel frequency-response is more severe at lower inversion biases, where the degradation of mobility and the increase of interface-trap concentration are both more significant. The maximum of the G₁(V) curve is very sensitive to the mobility and interface-trap concentration and can be used to monitor the degradation of the MOSFET. The degradation of the channel response due to high-field stressing is shown to depend on the gate-oxide thickness.