Modeling gate leakage current in nMOS structures due to tunneling through an ultra-thin oxide

For the first time, the tunneling current in silicon nMOS structures with ultra-thin gate oxides has been studied both by numerically solving Schrodinger's equation and by using the WKB approximation, which explicitly includes the size quantization effects in the inversion layers. The numerical solution employs first-order perturbation within the one-band effective-mass approximation to calculate the lifetime of an inversion-layer quasi-bound state. The good agreement in the tunneling currents estimated with these two methods justifies the use of the WKB approximation in the direct tunneling regime. The range of validity of the WKB approximation is also discussed. (C) 1998 Published by Elsevier Science Ltd. All rights reserved.