#### shaq

##### Full Member level 5

**Which one is correct?**

Dear all,

When I calculate K'n=(0.5)µnCox, I have a problem.

By TSMC 0.35µm SPICE model, I know these parameters (TT case):

(1) U0=0.04660162 (NMOS)

(2) tox=toxn=7.5e-9

(3) λ=DELTA= 0.01

(4)Vth0=0.536027

And, we know that ε=εox*ε0=3.9*8.854e-14F/cm=3.46e-11F/m

also know that Cox= ε/tox

so, we can get K'n=(0.5)*U0*Cox=0.5*0.04660162 *3.46e-11/7.5e-9=107.49µA/V

But, I use hspice to simulate a NFET which the result does not match to 107.49µA/V

Code:

```
Vgs g 0 1V
Vds d 0 0V
Vbs b 0 0V
*NFET
M1 d g 0 b NCH L=1u W=1u
.LIB 'mm0355v.l' TT
.options post probe
*For I-V Curve Id vs Vds with Vgs = 1V
.dc vds 0 3.3 0.01
.probe Id(M1)
.end
```

The figure of the result is shown below.

Because Vgs=1v and (W/L)=1, we can get Id=17µA

17µA=K'n(1-0.536027)^2*(1+0.01*3) , so we can get K'n=76.67µA/V

Can anyone tell me which K'n is correct?:?: