The main sources of leakage currents are :
- Reverse biased junction leakage current
- Sub threshold leakage
- Gate direct tunneling leakage
Reduction of gate oxide thickness results in an increase in the field across the oxide. This results in tunneling of electrons from substrate to gate and from gate to substrate through the gate oxide, resulting in gate oxide tunneling current.
This occurs from source or drain to the substrate through reverse biased diodes when transistor is off.
This is the drain to source current of transistor operating in the weak inversion region. Unlike the strong inversion region in which the drift current dominates, the sub threshold conduction is due to the diffusion current of minority carriers in the channel.