Threshold voltage fluctuation induced by direct tunnel leakage current through 1.2-2.8 nm thick gate oxides for scaled MOSFETs

Influences of direct tunnel leakage current through 1.2-2.8 nm thick gate oxides on nMOSFET DC characteristics have been investigated. It is found that the statistical distribution of the direct tunnel leakage current through the ultrathin gate oxides induces significant fluctuations in the threshold voltage and the transconductance of MOSFETs when the gate oxide tunnel resistance becomes comparable to gate poly-Si resistance. By calculating based on the measured characteristics it is shown that the threshold voltage and the transconductance fluctuations will be problematic when the gate oxide thickness is scaled down to less than 1 nm.