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how to determine the subthreshold process paramter?

MenghanSun

Dear all,

I have a question that i couldn't find an answer to in this forum. I wish to find out the subthreshold process paramter (sometimes referred to as process slope, subthreshold slope) of a given MOS device.

Id = u*Cox*(Vt^2)*(W/L)*exp( (VGS-Vth) / m*Vt ) * [1 - exp(-VDS/VT)]

The "m" is the subtreshold slope. I ran the DC simulation, use OPT on a MOSFET, I can find a big list of device parameters, region, self-gain, betaeff, and etc. However, I can't find the "m" the subthreshold slope.

Could anyone tell me how to find out the subtreshold slope "m" in cadence, Any help is appreciated. Thank you!

Menghan

  • Arefinn
    in reply to Andrew Beckett

    So you are saying it is not possible to plot or extract subthreshold slope factor n using this simulator? I would also like to add that this n is n = 1 + Cdep/Cox, hence is it possible to extract depletion layer and gate-oxide capacitancels repectively from this version of simulator? if so how?

  • Andrew Beckett
    in reply to Arefinn

    As I said in the earlier answer (before the one you replied to) you are trying to use some model equation of how a transistor works, and trying to fill in parameters of that based on a completely different model that was used in simulation. It's a common mistake that people use textbook equations which might have been valid 30 years ago and assume you can get exact results in modern (or even not so modern) technologies. This is not something to do with "this version of the simulator" - it's the fact that the device equations used in the models you are referring to do not use the equations you've quoted. You might be able to work out how to fit one set of (not particularly commonly used) equations onto the equations actually simulated, and extract the numbers you're looking for, but this is a slightly odd thing to do...

    Since this subthreshold slope factor is not part of the device models used, there's nothing in the simulator to output it. I cannot find it used in any of the models (other than the Philips/NXP models I mentioned before, and even then I'm not sure it means the same thing).

    Other than this question being asked here (twice) - presumably the earlier question came about from the same book - I've not found anyone asking this question anywhere. I'd be surprised if any simulator directly outputs this value.

    Andrew.

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