Current conduction of a MOSFET in saturation region

Thread Starter

Babun Pal

Joined Jul 13, 2016
17
Hi,

Could anyone please explain me how would the current conduction take place if the channel of a MOSFET is pinched off?

Thanks in advance.
 

dl324

Joined Mar 30, 2015
12,873
Nope - this is normal forward conduction. See the explanation in post #2.
Nope, it's leakage current. WIth zero gate bias, all MOSFETs will have leakage current. This is especially true for short L and thin gate oxide devices.
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Last edited:

AlbertHall

Joined Jun 4, 2014
11,319
OP is talking about conduction when the MOSFET is off. Both of your cartoons show the transistor on.
OP is specifically talking about MOSFET conduction while the channel is pinched off - the situation depicted in the diagrams I posted.
Channel pinch off is NOT what happens when the gate voltage is below the threshold.
From the link I posted in post #2:
"What happens between the pinch-off point and the Drain:
The Gate-to-Substrate voltage in this region is not enough for a formation of the inversion layer, therefore this region is only depleted (as opposed to inverted). While depletion region lacks mobile carriers, there is no restriction on current flow through it: if a carrier enters the depletion region from one side, and there is an electric field across the region - this carrier will be dragged by the field. In addition, carriers which enter this depletion region have initial speed.

All the above is true as long as the carriers in question will not recombine in the depletion region. In n-type MOSFET the depletion region lacks p-type carriers, but the current consist of n-type carriers - this means that the probability for recombination of these carriers is very low (and may be neglected for any practical purpose).

Conclusion: charge carriers which enter this depletion region will be accelerated by the field across this region and will eventually reach the drain. It is usually the case that the resistivity of this region may be completely neglected (the physical reason for this is quite complex ... )."
 
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