Why in lowleakage applications transistors with minimum L sh

Why in low-leakage applications transistors with minimum L should not be used?

Solution

why in low leakage transistors with minimum L should not used

1) When more than one transistor is in series in a CMOS circuit, the leakage current has strong dependence on the number of turned off transistor. This is known as stacking effect.   

2) The highest leakage current is 99 times that of the lowest leakage current, A suitable input combination is used such that the reduction in leakage current due to stacking effect is maximized.

3) decrease in the channel length (L) will increase Xd (drain-induced barrier lowering) So, any increase in the leakage of a single transistor due to decrease in L will not increase leakage of a two-stack at the same rate and increase in two-stack leakage is at a slower rate than that of a single transistor.

4) Therefore, variation in L will result in smaller effective threshold voltage variation for a two-stack compared to a single transistor.