Find Threshold voltage from Id-Vgs

[fat_123]

Hi,

Could anyone tell me how to find the threshold voltage from Id-Vgs characteristic in HSPICE?

Regards

 

[sutapanaki]

Vth is really an approximation. What will happen if in your plot you convert you vertical axis to a logarithmic scale?

 

[fat_123]

It is basically for beyond CMOS technology.

Its logarithm plot looks like this.

vgs=sweep from 0 to vdd
vd=vdd/2

 

[sutapanaki]

The initial linear part of the curve is weak inversion, then a transition to moderate inversion adn finally strong inversion. So, if we believe the simplified theory that weak inversion is also sub-threshold region, then your threshold is somewhere at the meeting point of weak inversion and moderate inversion. But it is fuzzy.

 

[dick_freebird]

For modeling purposes regress the sqrt(Id) vs Vgs curve
to its y-intercept. If you want to use a MOS model,
or just to talk to MOSFET people.

 

[fat_123]

this is not a MOSFET, its an NCFET(negative capacitance feet) which works in subthreshold region.

 

[dick_freebird]

Well, if you have a different model in mind then its
parameters ought to be documented and the equation
(or equations) that contain "VT" can be back-solved in
the same manner.