# why pmos threshold bigger than its nmos couterpart?

1. ## why pmos threshold bigger than its nmos couterpart?

I mean abosulute value. Why this happens? Can anyone tell me ,thank you!

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2. ## why pmos threshold bigger than its nmos couterpart?

it is due to mobility of the carrier that forms the channel...

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3. ## Re: why pmos threshold bigger than its nmos couterpart?

A well-known formula for the threshold volatge:

$3V_{TH}=\Phi_{MS}+2\Phi_{F}+\frac{Q_{dep}}{C_{ox}}$

Fermi potential: $3\Phi_{F}=\frac{kT}{q}\ln\frac{N_{Sub}}{n_{i}}$

$3Q_{dep}=\sqrt{4q\eps_{Si}|\Phi_{F}|N_{Sub}}$

It is not an accurate formula, but it pushes you to the right way.

Usually the difference between the PMOS and NMOS threshold voltages is approx. 100 mV.
I doubt it is because of the mobility.
I guess it is because of the differences in doping.

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4. ## why pmos threshold bigger than its nmos couterpart?

I think it depends on vth implant by the foundry.

5. ## why pmos threshold bigger than its nmos couterpart?

PMOS have two doping i,NWELL implant and P+ implant.

6. ## why pmos threshold bigger than its nmos couterpart?

Hi
I think the threshold voltage of NMOS and PMOS can be modified to a same level by the doping.

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7. ## why pmos threshold bigger than its nmos couterpart?

I think, too...Possible to make a techology with same threshold voltages.

But I guess it is not so important and determine a technology is a trade-off between many things.
Doping level is very important in breakdown, resistance , etc.

8. ## why pmos threshold bigger than its nmos couterpart?

Yes, PMOS threshold for absolute value can be changed less than NMOS with threshold implant.

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