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  1. #1
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    Short channel effects on Transconductance(gm).

    Hiii....

    i have plotted Gm vs Vgs graph,as shown below please help me to analyse that graph, why it rises suddenly, why it start to decrease, which parameter is responsible for this kind of behaviour ?
    please help to know what are the short channel effects affects the transconductance ?
    i know gm is affected by velocity saturation and some mobility degradation issues but i am focussing on shape of the cure.
    Click image for larger version. 

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  2. #2
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    Re: Short channel effects on Transconductance(gm).

    gm is the slope d(Id)/d(Vgs). Look at the basic ID-VG
    curve and you can see that there's a slope that's
    maximum and consistent, in the subthreshold region
    (thus maximizing gm) and it rolls over as the FET goes
    into strong saturation.

    This has not to do with short channel per se.

    Short channel brings you some non-classical device
    features (like halo implants and strong LDDs), which add
    source resistance and may lower the point where dId/dVgs
    rolls over - source degeneration matters when Id*Rs
    becomes a significant fraction of VT0.

    DIBL will move the gm peak depending on drain voltage,
    more than long channel devices (your peak gm does not
    stay put with common mode position varying).



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