Analytical study of impact ionization and subthreshold current in submicron n-MOSFET

The effect of impact ionization in subthreshold operation of an n-MOSFET is studied. Analysis shows that the effect of impact ionization cannot be neglected in the subthreshold region of operation of the submicron MOSFET. This effect is enhanced at larger drain voltages. Gate bias and oxide thickness controls the effect of impact ionization. The effect of impact ionization is through the gate and drain bias dependence of the maximum electric field. The subthreshold current increases when the gate oxide is thinned. This is because of the increase in impact ionization due to the increase in electric field.