Gate tunnel current in an MOS transistors

A theoretical description of gate tunnel current in an MOS transistor is presented, and the results of calculations for the case of an n-channel MOSFET with extremely thin gate oxides are given. A comparison shows that the gate tunnel current is low in comparison with the drain current, even in the case of extremely thin gate oxides. This is in agreement with experimental results published in the literature. It is concluded that the minimal gate oxide thickness in MOS/VLSI circuits will result if very good quality ultrathin oxides are realized in a controllable way rather than from the flow of too large a gate tunnel current. However, in some circuit applications of the MOS transistor the problem of input leakage current can be especially important, and then gate tunnel current can limit the minimal oxide thickness