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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

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  • Andrew Beckett

    Unknown said:
    This is not a particular model. This is a general fact

    No, it's a model. All equations describing MOSFET behaviour are models which are an attempt to fit the physical behaviour to a certain level. The precise equations will vary from one model to another. Even in the slide you refer to, it's described as a model.

    The fact that you're using a particular model to gain design insight is fair enough, and most of us do that, but you can't necessarily expect a simulator to output a parameter which works for the particular model you're using (and is different from the model the simulator is actually using). The models in the simulator will model the subthreshold behaviour you describe, but won't necessarily do it with the equation you're describing (especially as it's incomplete).

    Regards,

    Andrew.

Reply
  • Andrew Beckett

    Unknown said:
    This is not a particular model. This is a general fact

    No, it's a model. All equations describing MOSFET behaviour are models which are an attempt to fit the physical behaviour to a certain level. The precise equations will vary from one model to another. Even in the slide you refer to, it's described as a model.

    The fact that you're using a particular model to gain design insight is fair enough, and most of us do that, but you can't necessarily expect a simulator to output a parameter which works for the particular model you're using (and is different from the model the simulator is actually using). The models in the simulator will model the subthreshold behaviour you describe, but won't necessarily do it with the equation you're describing (especially as it's incomplete).

    Regards,

    Andrew.

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