Electron mobility - want to calculate K'=u*Cox of mosfet

[lionelgreenstreet]

Electron mobility

I'm not sure if this is the right place.....
I want to calculate K'=u*Cox of mosfet...i don't understand why it depends on W and not only on L.....u=Vdrift/e with e=electric field=V/L : if V is the same and L increases, than u increases...but, what is its relationship with W?
Another question: modulation channel parameter depends only on L or also on W?
Thanks

 

[subharpe]

Re: Electron mobility

Cox will definitely depend on the width W of the channel, as the oxide layer cap depends on the cross-sectional area area of the channel under the oxide layer.

 

[lionelgreenstreet]

Re: Electron mobility

I Know:
K'=u*C'ox
with
u=electron mobility [cm^2/V*sec]
C'ox= gate capacitance/unit area [F/cm^2]

K'*W/L=beta

I'm wrong?If no, C'ox not depends on W/L....can you help me?

 

[nschutten]

Re: Electron mobility

please look at https://en.wikipedia.org/wiki/Electron_mobility
Untuitively I would say that the mobility depends on the electric field, which is proportional to V/m (or inversly m/V) and that the speed is m/s, so that you'd have something proportional to m2/Vs

 

[neils_arm_strong]

Electron mobility

You are missing something here. Mobility is a constant for small electric fields.You cannot state that u=Vdrift/E.In fact Vdrift=u*E gives a correct meaning that drift velocity is the velocity acquired by electron for unit electric field.
As far as your doubt is concerned, as L increases , E=V/L decreases and as a result Vdrift decreases and thus the ratio Vdrift/E remains constant.
Correct me if i am wrong