Sub threshold leakage is basically the leakage when the gate voltage is less than threshold voltage.
So, when the supply is less than Vt , we dont expect any current. But, due to charges there is a possibility of current flow from Source to drain and we term it as Sub threshold leakage
Technology :
If the library is Low Vt then the sub threshold effect will be more compared to HVT library.
Thanks for the reply. I'm familiar with the concept. I guess I didn't describe my question very well. If we lower the VDD (but not under the threshold voltage) does it affect subthreshold voltage?
Yes, I hope you are talking about the drain voltage variation.
If the Drain voltage is more, more Diffussion area will be present in Drain region and hence more leakage.
Eg : Vdrain = 5V will have more leakage than Vdrain = 3V keeping Vt=1V .