SRF Tech
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Posts: 59
Arizona
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Aaron, A lot really depends on your process. Example, If you are using an Nwell resistor on a Bulk Silicon process, generally the nwell has an STI built between the two contact ends of the resistor. I have seen nwell resistors vary dramatically because of this, as the STI depth is not a tightly controlled dimension, creating a lot of variation. I personally have seen nwells change by >50% on some processes, within the same die. Again it was because the STI depth was not tighly controlled at all. Poly resistors tend to be much better because their physical dimensions are more tightly controlled, as is the doping profile.
Ultimately you need to trust what the foundary is telling you about the resistors, because they know which factors affect the resistances and how well they control those factors. Of course the caveat here is I have seen foudaries that did not even model temp-co for their resistance (that was a pain).
Your good experience with the npoly unsalicide resistor, may very well be unique to that process, I would not base work you do on other processes on that one experience. Hope this helps, Stephen
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