Limit of gate oxide thickness scaling in MOSFETs due to apparent thresholdvoltage fluctuation induced by tunnel leakage current

We report on a new roadblock which will limit the gate oxide thickness scal ing of MOSFETs. It is found that statistical distribution of direct tunnel leakage current through 1.2 to 2.8 nm thick gate oxides induces significant fluctuations in the threshold voltage and transconductance when the gate o xide tunnel resistance becomes comparable to gate poly-Si resistance. By ca lculating the measured tunnel current based on multiple scattering theory, it is shown that the device characteristics fluctuations will be problemati c when the gate oxide thickness is scaled down to less than 1 nm.