Explain in detail about effect and its effect in MOS device

Threshold voltage Vt increases with the source voltage, decreases with the body voltage, decreases with the drain voltage and increases with channel length.

Body Effect:

 When a voltage Vsb is applied between the source and body, it increases the amount of charge required to invert the channel. Hence, it increases the threshold voltage.

 The threshold voltage can be modeled as

(iv) Leakage:

•  Even when transistors are OFF, transistors leak small amounts of current.
•  Leakage mechanisms include subthreshold conduction between source and drain, gate leakage from the gate to body and junction leakage from source to body and drain to body.
•  Subthreshold conduction is caused by thermal emission of carriers over the potential barrier set by the threshold.
•  Gate leakage is a quantum-mechanical effect caused by tunneling through the extremely thin gate dielectric.
•  Junction leakage is caused by current through the p-n junction between the source/drain diffusions and the body.