New instability in thin gate Oxide MOST´s

New instability in threshold voltage VTand transconductance gmdue to Fowler-Nordheim (F-N) tunneling current through the gate oxide was studied for thin gate oxide n-channel MOST´s. The tunneling current under both positive gate bias and negative gate bias causes threshold voltage shift toward enhancement and transconductance degradation. The instability is basically a function of the total tunneling charge and can be quickly recovered by low temperature anneal. Finally we show that the instability can be systematically explained by increase in fast surface states not only in the subthreshold region but also in the strong inversion region.