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# how we calculate Cox?

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#### mohazaga

##### Full Member level 2
cox tox

Hi..
how we can calculte the Cox of CMOS using the parameters of
Pspice CMOS model TSMC 180nm .
thanx[/u]

cox mosfet

you need to use tox(thickness of oxide)
Cox=E0*Er/tox
E0=8.854e-12F/m
Er=3.9 for SiO2
Make sure you use tox in meters to end up with Cox with units F/m^2.
Usually Cox is written as F/(um)^2

Points: 2

Points: 2

### electronicuser

Points: 2
cox cmos

Hi ,
Tox = 4E-9 m from PSpice model of TSMC's 180nm MOSFET process .
E0=8.85E-18 F/um (Jacop Backer : CMOS circuit design ... , pp114)
Er=3.97 , same book
Cox=E0*Er/tox
Cox=8.784E-15F/um²

is that ok
Thanx

fateme m

### fateme m

Points: 2
cox mos

hi,

Cox = Eox/Tox

Eox = er*eo
Tox = thickness of oxide

calculate cox

Hi, I have the following model

.model Mbreakp PMOS
level=2
ld=0.21e-6
kp=28e-6
vto=-0.87
gamma=0.70
phi=0.72
cj=0.62e-3
cjsw=0.26e-9
cgso=0.42e-9
cgdo=0.42e-9
cgbo=0.3e-9
nsub=8.8e16
nfs=1e10
tox=200e-10
xj=0.3e-6
ucrit=1.2e4
uexp=0.063
delta=2
kf=7e-15
af=1.2

and I want to calculate K=1/2 uCox
From the above I can find Cox. But what about u is it constant and what is its value?
(u: mobility)

Thanks

mosfet cox

thuvu said:
Hi, I have the following model

.model Mbreakp PMOS
level=2
ld=0.21e-6
kp=28e-6
vto=-0.87
gamma=0.70
phi=0.72
cj=0.62e-3
cjsw=0.26e-9
cgso=0.42e-9
cgdo=0.42e-9
cgbo=0.3e-9
nsub=8.8e16
nfs=1e10
tox=200e-10
xj=0.3e-6
ucrit=1.2e4
uexp=0.063
delta=2
kf=7e-15
af=1.2

and I want to calculate K=1/2 uCox
From the above I can find Cox. But what about u is it constant and what is its value?
(u: mobility)

Thanks

Hi,

If you are using the BSIM3v3 model, than you can use u0 as u. I noticed that u0 isn't defined in your model, so you can use the default values of u0.
For a NMOS: u0 = 670 cm^2/(V*s)
For a PMOS: u0 = 250 cm^2/(V*s)
u0 is defined as the Low-field surface mobility at 'tnom'. So from it's definition it is seen that there is a temperature dependence of u0. However, size of W and L of your transistor also have an influence on the value of u.

I found the default values for u0, by typing the command "spectre -help bsim3v3" on the command line (I'm assuming you are using candence to).

Hope it helps you

how to calculate cox

Thanks Steven

The thickness of gate oxide is obtained from model
parameters given by MOSIS and is 300 Å. For W/L = 8.0 mm/1.6 mm,

300A where the value is obtained

The thickness of gate oxide is obtained from model

... where the value is obtained
From the model file. Search for TOX .

u0 is a surface mobility, which is different than the well
characterized and fairly consistent bulk mobility. It
depends a lot on surface (underside of gate ox) quality
and this is very process-variable.

For Tox, you may see reported an optical and/or an
electrical Tox in foundry data; electrical Tox may
include things like poly depletion making it generally
larger, but more accurate for device modeling, than
the optical Tox that inline controls tend to observe.

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