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    Why is pmos and nmos put vertically and not side by side(horizontally)in ic layouts?

    Is it because of convention or because wires would be longer ?

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    Re: Why is pmos and nmos put vertically and not side by side(horizontally)in ic layou

    planar IC fabrication is "side by side", vertical MOS channels are not existing or at least not conventional, I have never saw it. Or what do you mean under they are put vertically?
    Go through a fabrication process I think, like this one: https://www.edgefx.in/understanding-...on-technology/
    "Try SCE to AUX." /John Aaron/



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    Re: Why is pmos and nmos put vertically and not side by side(horizontally)in ic layou

    Quote Originally Posted by 94d33m View Post
    Is it because of convention or because wires would be longer ?
    Some old technologies allowed you to build wells any way you wanted and you could put p and n side by side instead of on top of each other. it gets tougher with newer nodes, thus the restriction.
    Really, I am not Sam.



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    Re: Why is pmos and nmos put vertically and not side by side(horizontally)in ic layou

    I have yet to work in any technology that's so constrained, but
    I've sat through presentations about it.

    "Back in the day" it was all just about maximum logic cell density.
    And that is usually driven by layouts more complex than 1-,
    2-input logic gates. Routing just works out better with the
    gates vertical, power horizontal, maybe 3 channels in the middle
    for local interconnect (plus dropping out contacts here and there).

    I've had my eyes on and fingers in maybe a dozen different CMOS
    standard cell libraries and all pretty much the same across maybe
    6 fabs and 4 companies and several decades. But the leading edge
    bears less and less resemblance to the trailing edge, as we go.



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    Re: Why is pmos and nmos put vertically and not side by side(horizontally)in ic layou

    I have Worked on 22FDX and 28nm node Technology and there is no convention of placing nmos and pmos in a particular fashion you can either put pmos and nmos side by side or one down the other!!
    If we talk about channel:
    Well in planar IC you will never see a vertical channel ,the channel is always horizontal i.e it is recommended to place the poly in vertical direction(which makes channel horizontal) but in 55nm node it wasn't the case so as we go down the lower nodes it is recommended to keep the channel horizontal.
    I hope this helps
    Last edited by Vishu21_95; 3rd July 2019 at 06:57.



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    Re: Why is pmos and nmos put vertically and not side by side(horizontally)in ic layou

    Quote Originally Posted by dick_freebird View Post
    I have yet to work in any technology that's so constrained, but
    I've sat through presentations about it.
    I am not a process guy, but the information that was relayed to me is that the lower layers are so hard to print/dope that the machinery is optimized to work in only one direction. i.e., fins are always horizontal. think of a stepper machine. it probably is easier to make something that has only one degree of control in one axis instead of two.
    Really, I am not Sam.



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  7. #7
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    Re: Why is pmos and nmos put vertically and not side by side(horizontally)in ic layou

    Quote Originally Posted by ThisIsNotSam View Post
    I am not a process guy, but the information that was relayed to me is that the lower layers are so hard to print/dope that the machinery is optimized to work in only one direction. i.e., fins are always horizontal. think of a stepper machine. it probably is easier to make something that has only one degree of control in one axis instead of two.
    Yeah this can be the case!! More the advantage of keeping pmos and nmos vertically is that all the pmos can contained in a single well which will not be possible of you keep them side by side.



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