MOSfet , the operation of sub-threshold region

Subthreshold leakage is the current that flows from the drain to source of a MOSFET when the transistor is supposed to be off.

In the past the subthreshold leakage of transistors has been very small, but as transistors have been scaled down, subthreshold leakage can compose nearly 50% of total power consumption. The reason for this is that the supply voltage has continually scaled down to reduce the dynamic power consumption of integrated circuits (the power that is consumed when the transistor is switching from an on-state to an off-state) which depends on the square of the supply voltage. As the supply voltage is scaled down, to maintain performance, the threshold voltage has to be reduced in the same proportion. As threshold voltages are reduced, subthreshold leakage rises exponentially.

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