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https://designers-guide.org/forum/YaBB.pl Modeling >> Semiconductor Devices >> nonlinearity of poly-poly or MIM caps https://designers-guide.org/forum/YaBB.pl?num=1223964187 Message started by vivkr on Oct 13th, 2008, 11:03pm |
Title: nonlinearity of poly-poly or MIM caps Post by vivkr on Oct 13th, 2008, 11:03pm Hi, There is a small nonlinear component even in linear caps such as poly-poly or metal-metal, which is important when designing very precise analog circuitry. Typically, the nonlinearity is much less than 100 ppm/V. Intuitively, I would expect the nonlinearity to be quadratic, i.e. C(V) = C0 + C2(V^2), as I would imagine that the polarity of the applied voltage has no (or very little) influence on the nonlinearity, and only the magnitude matters. However, I often see a linear term here, and C(V) = C0 + C1(V) + C2(V^2) The linear term appears to be not insignificant. Why would there be a linear term at all? Regards, Vivek |
Title: Re: nonlinearity of poly-poly or MIM caps Post by rf-design on Oct 14th, 2008, 1:32am I assume that the linear term is steeming from a space charge effect similar to a MOS cap. Typical linear caps in submicron are obtained by canceling two opposite nonlinear terms. It could also be a extraction artifact where the linear term was not set to zero in a more general extraction routine. http://www.ece.nus.edu.sg/stfpage/elelimf/pub(updated_20Nov2004)/Kim%20VLSI%2004.pdf |
Title: Re: nonlinearity of poly-poly or MIM caps Post by thechopper on Oct 14th, 2008, 7:14pm Hi Vivek, I'm just guessing, but since usually the parasitics on the cap bottom plate is different from the one on the upper plate I would tend to think the sign of the applied voltage might be important. If that was the case then it makes some sense to have a non-insignificant linear term in the capacitor model as a function of the applied voltage... Regards Tosei |
Title: Re: nonlinearity of poly-poly or MIM caps Post by vivkr on Oct 21st, 2008, 10:57pm Thanks to everyone for the very useful answers and references. Now things seem a bit clearer. Regards, Vivek |
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