The Designer's Guide Community Forum

The Designer's Guide Community Forum
https://designers-guide.org/forum/YaBB.pl
Modeling >> Semiconductor Devices >> How are Vtlin and Vtsat extracted from simulation results
https://designers-guide.org/forum/YaBB.pl?num=1296566798

Message started by modelman on Feb 1^st, 2011, 5:26am

Title: How are Vtlin and Vtsat extracted from simulation results
Post by modelman on Feb 1^st, 2011, 5:26am

I often see curves that show VTlin vs Length or VTsat vs Length VTlin vs width, VTsat vs width etc.

I know how to create a netlist to sweep Length or Width and look at drain current.

Could you please explain how can I back calculate the threshold voltage?

Title: Re: How are Vtlin and Vtsat extracted from simulation results
Post by Geoffrey_Coram on Feb 1^st, 2011, 10:03am

Experimentally, I think people usually sweep VG and define VT by a feature of the ID-VG plot; then they repeat this for the available widths on the test chip.

You could do the same in simulation, or, if you like the definition of VT reported in the op-pt info of your simulator, you can sweep W or L and look at the op-info.

Title: Re: How are Vtlin and Vtsat extracted from simulation results
Post by modelman on Feb 1^st, 2011, 12:48pm

Thank you Geoffrey.

Is there a standard that is followed in calculating Vt from Id?

I recall mention of 300mA but I am not sure what it refers to. I guess the device gets biased to produce Id=300mA and Vt is calculated based on a simple expression for Id as a function of mu, cox, W, L, Vgs, Vds and Vt

I suspect one would get different Vt values using this approach at different values of Vgs and Vds (clearly Vt is a function of bias, otherwise there would not be different values for Vtlin and Vtsat)

What am I missing here? :-?
Thanks.

Title: Re: How are Vtlin and Vtsat extracted from simulation results
Post by Mooraka on Feb 1^st, 2011, 3:24pm

I think for scaled technologies, Vt is usually calculated using constant current method. For eg. Vtlin is defined as Vgs at Ids=300nA*(W/L) and Vds=50mV. Vtsat is calculated similar way but at Vds=Vcc.

You can check your Technology/Foundry documentation for exact definition/Id numbers.