Why there is more variation in nwell resistor?

[khotkar]

Nwell resistor

Can anybody tell me "Why there is more variation in nwell resistor?"

 

[erikl]

Re: Nwell resistor

"Why there is more variation in nwell resistor?"

nwell is a real, lightly doped, i.e. relatively high-ohmic semiconductor material, as such has a much higher voltage dependency and a distinctively higher temperature dependency than, e.g., polysilicon, which is a highly-doped, relatively low-ohmic, thus already degenerated semiconductor, whose conductivity mechanism is caused by less semiconductor-like but more metal-like conductivity, thus exhibits much lower voltage and temperature dependencies. Metal resistors, of course, show still much lower VT dependencies.

 

[khotkar]

Re: Nwell resistor

Thanks buddy.

 

[sandeep_torgal]

Re: Nwell resistor

"Why there is more variation in nwell resistor?"

nwell is a real, lightly doped, i.e. relatively high-ohmic semiconductor material, as such has a much higher voltage dependency and a distinctively higher temperature dependency than, e.g., polysilicon, which is a highly-doped, relatively low-ohmic, thus already degenerated semiconductor, whose conductivity mechanism is caused by less semiconductor-like but more metal-like conductivity, thus exhibits much lower voltage and temperature dependencies. Metal resistors, of course, show still much lower VT dependencies.

Am still unclear about what u said... The variation is due to the process shifts is what i thought.

 

[kenliao18]

Nwell resistor

nwell is built on the substrate,noises from the substrate will easily affect the nwell resistor.
and just as erikl have said, it is VT dependent.

 

[sandeep_torgal]

Re: Nwell resistor

nwell is built on the substrate,noises from the substrate will easily affect the nwell resistor.
and just as erikl have said, it is VT dependent.

Then u mean that to find out the resistance of a nwell resistor we need to calculate the substrate noise and the resistance varies because of that..

 

[erikl]

Re: Nwell resistor

Am still unclear about what u said...

Am sorry 4 u ;-)

The variation is due to the process shifts is what i thought.

Sure; but this P-dependency results in the same variation contribution to all types of resistors and other devices on the chip. It doesn't explain the large differences of their VT dependencies between e.g. active-p, active-n, nwell, high-poly, low-n-poly & low-p-poly resistors.

Added after 27 minutes:

nwell is built on the substrate,noises from the substrate will easily affect the nwell resistor.
and just as erikl have said, it is VT dependent.

... to find out the resistance of a nwell resistor we need to calculate the substrate noise and the resistance varies because of that..

No, not at all: noise doesn't influence the resistor value (only the other way round). I guess, kenliao18 just meant that nwell resistors (like active-p & active-n resistors) are very prone to pick up noise from nwell (or substrate, for active-n resistors).

 

[ravirajdv]

Re: Nwell resistor

Hi,
If you look at the equation for Resistance, resistance is a strong function of TC of the material used. As ekril suggested the nwell resistance has more dependence on T than Poly resistor or a metal resistor, which signifies the increasing order of the doping concentration (conductivity) of the material. To add to this, if we take a poly resistance alone, the temp dependence of the poly varies depending whether the poly is n-doped or p-doped.
The same case also applies to the active resistors.

Regards,
RDV