- If the inversion layer-substrate (or the source-substrate or the
drain-substrate) junction ever gets forward bias, a large leakage current
would result, which would hamper normal MOSFET operation.
- For both n- and p-channel MOSFETs, the magnitude of the threshold
voltage VT increases with an increase in |Vsub|.
Physical Understanding of Saturation
- A physical insight into the phenomenon of saturation may be obtained
by analyzing the electric field distribution under the gate.
- Integrating Eq.(5.6) from 0 to x, one gets :
or
- The electric field
 in
the channel in the direction parallel to the semiconductor-insulator
interface can be found from Eq.(5.5)
:
- Solving Eqs.(5.12) and (5.13) together, the field profiles can be
calculated.
Fig.5.6 The variation of the electric field along the channel for drain
voltage nearly equal to the saturation voltage for gate voltages
|