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Extraction of parasitic parameters of a MOS transistor used like switch

Ueue

Dear all,

I need to have a precise estimation of the parasitic capacitances of my MOSFETs, used as switches. I was thinking, for the measure of capacitances to impose a voltage source with voltage Vs increasing linearly with time and measuring the current (proportional to the capacitances). So Vs=K*t. For example connecting the generator to the gate, and the other terminals to ground, I could measure the Cgd and Cgs. Is it a good method?

Thanks a lot,

Stefano

Parents

  • Hi there,

    I have the same problem. I have search all over the web, thesis, forum, etc and I just can't reach a conclusion. I read that one coud use the print OP and use those values, I read that one should use transient/AC analysis to get a more accurate value however this was contested by some user in the forum that I read that, and so on.

    The feeling that I have is that:

    1st. People doesn't want to share how this is done;

    2nd. No one knows and they are just commenting in forums;

    I need to design a chain of inverters (drivers) to drive my power devices and I don't have any starting point.

    Regarding the negative capacitances, that is related to the way the spectre/bsim model does the math. My problem is to know if we can ignore that "minus" sign in order to use the capacitance that we get from print OP (if this is the way to get the capacitances).

    Taking the advantage of this post, I'd like to know if someone can tell me:

    1st. How can I get the Kn,p value? (I know that Kn,p = un,p Cox and for that;

    2nd. How can I estimate the Cox? From the technological documentation I have access to the extracted Tox from the foundr. I can use this value and the respective known equatio to get the Cox? This leads to;

    3rd. If I can do that, then I can estimate the capacitances using the Cox and the basic equations do compute the Cgs, Cgd, Cgb etc?

     

    Regards.

    Hope get some answers here....

Reply

  • Hi there,

    I have the same problem. I have search all over the web, thesis, forum, etc and I just can't reach a conclusion. I read that one coud use the print OP and use those values, I read that one should use transient/AC analysis to get a more accurate value however this was contested by some user in the forum that I read that, and so on.

    The feeling that I have is that:

    1st. People doesn't want to share how this is done;

    2nd. No one knows and they are just commenting in forums;

    I need to design a chain of inverters (drivers) to drive my power devices and I don't have any starting point.

    Regarding the negative capacitances, that is related to the way the spectre/bsim model does the math. My problem is to know if we can ignore that "minus" sign in order to use the capacitance that we get from print OP (if this is the way to get the capacitances).

    Taking the advantage of this post, I'd like to know if someone can tell me:

    1st. How can I get the Kn,p value? (I know that Kn,p = un,p Cox and for that;

    2nd. How can I estimate the Cox? From the technological documentation I have access to the extracted Tox from the foundr. I can use this value and the respective known equatio to get the Cox? This leads to;

    3rd. If I can do that, then I can estimate the capacitances using the Cox and the basic equations do compute the Cgs, Cgd, Cgb etc?

     

    Regards.

    Hope get some answers here....

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