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What happens to threshold voltage when doping concentratio of substrate is increased?

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brahma

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what will happen to the thershold voltage of enhancement type MOSFET when i (i)increase the doping concentration of substrate,
(ii)increase the width of the oxide layer??
 

pankaj waghmare

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thershold voltage

im mosfet substrate acts as a another gate to mosfet.increasing doping has a definately affected the current.
asn in current eqn of mosfet id is directly proportional to cox which is equal to (eox/tox). tox is oxide thickness so clearly u can get the idea.
 

electronics_kumar

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thershold voltage?

brahma said:
what will happen to the thershold voltage of enhancement type MOSFET when i (i)increase the doping concentration of substrate,
(ii)increase the width of the oxide layer??

it will be decreased...
 

abcyin

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increasing doping concentration increases vt

(i) if you increase the doping concentration of sub, it means that the majority carriers concentration is increased, the Vgs for depletion and inversion is increased,that's to say, the threshold voltage is increased.
(ii) if you increase the width of the oxide layer, the cap of the oxide layer will be decreased, the change of charge is not so sensitive with the change of Vgs, so, the Vth will be increased.

the threshold voltage is related with
1,the doping concentration of the sub,
2,the work function between the gate and the sub
3,the impurities in the oxide layer
4,tox of the oxide layer
 

bjeservice

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thershold voltage

i think
1. increasing concentration of substrate will decrease Vt
2. increasing thickness of oxide layer will increase Vt which is bad effect
 

Gautam Nani

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Re: thershold voltage

i think
1. increasing concentration of substrate will decrease Vt
2. increasing thickness of oxide layer will increase Vt which is bad effect


The electron that are released from the dopant atoms in the substrate move randomly in the substrate when there is not supply applied. When there is an electric field in the channel the electrons start moving in a particular direction from source to drain. The voltage required to make the randomly moving electrons to go in a specific path is called as threshold voltage.

So as the dopant concentration increases in the same substrate, the number of electrons offered by the dopant atoms too increase. when the electron number increases in the same substrate area the random collisions increase because of more density and it is difficult to control the electrons and make them flow in a particular direction. So more voltage is needed to control and this voltage to overcome the randomness of the electrons is called as threshold voltage and it increases with increase in dopant concentration.

Let me know if there are any points in the explanation above where you contradict with my view.

Thanks,
Gautam Nani
 

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