Gate current in ultrathin MOS capacitors: a new model of tunnel current

We have deduced the analytical expression of the tunneling current across a thin oxide layer for a MOS capacitor, by introducing a new double-box simplified model of the oxide layer. We have developed this model to study some characteristics of the tunneling current, which are neglected when the usual Fowler-Nordheim description is adopted. Matching between experimental and simulated curves is excellent, and no free parameter is needed to adjust the fitting quality, once the values of the main physical parameters are chosen. The model quantitatively describes the quantum oscillations of the gate current produced by the interference between the coherent incident electron-wave and the electron-wave reflected at the oxide/anode interface. From the period of the quantum oscillations, we have deduced a semiempirical relation useful to evaluate the oxide thickness. The quantum oscillations amplitude is related to the oxide/anode interface roughness, which is accounted for by a rugosity parameter introduced in our model. The temperature dependence of the tunneling current has been taken into account as well in two parameters of the model