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iVenky Senior Member Offline Posts: 101 Silicon Valley	Does the threshold voltage of MOS transistors vary with fingers? Mar 31^st, 2016, 10:26am Hi, I would like to know if the threshold voltage of MOS transistors vary with the number of fingers in these advanced technologies. I mean compared to multipliers, does the threshold vary? Thanks!
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loose-electron Senior Fellow Offline Best Design Tool = Capable Designers Posts: 1638 San Diego California	Re: Does the threshold voltage of MOS transistors vary with fingers? Reply #1 - Mar 31^st, 2016, 11:09am As a guess, probably not. Important that you get your foundry specific data to get a meaningful answer.
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davidshw Junior Member Offline Posts: 12 China	Re: Does the threshold voltage of MOS transistors vary with fingers? Reply #2 - Mar 31^st, 2016, 11:40pm yes, dut to LOD and WPE stree effect, the vth is different of different fingers, the matching MOS devices (such as current mirror) should have the same fingers in pre-simulation.
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raja.cedt

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Germany

Re: Does the threshold voltage of MOS transistors vary with fingers?
Reply #3 - Apr 1^st, 2016, 2:18am

Multipliers are separated by ST kind of isolation, so fingers adjacent to STI will have higher stress during manufacturing. Where as fingers are adjacent to another finger hence no stress. So Vth strongly depends on where they are.

Please refer LOD and STI effects in Google.

Best regards,
Raj.

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loose-electron Senior Fellow Offline Best Design Tool = Capable Designers Posts: 1638 San Diego California	Re: Does the threshold voltage of MOS transistors vary with fingers? Reply #4 - Apr 3^rd, 2016, 6:58pm Go get empirical data to validate. Too many times I have seen things like thins go in a different direction. Real world data from real world silicon.
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RobG

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Bozeman, MT

Re: Does the threshold voltage of MOS transistors vary with fingers?
Reply #5 - Apr 11^th, 2016, 12:58am

raja.cedt wrote on Apr 1^st, 2016, 2:18am:

Multipliers are separated by ST kind of isolation, so fingers adjacent to STI will have higher stress during manufacturing. Where as fingers are adjacent to another finger hence no stress. So Vth strongly depends on where they are.

Please refer LOD and STI effects in Google.

Best regards,
Raj.

This is true, but I haven't had to lay them out that way to pass LVS. For example, if the device was M=10, NF=2, you could lay it out as M=1, NF=20 and pass LVS. Extracted simulations are real important to model this sort of stuff.

Dummy devices should be used so the surroundings are the same no matter how many fingers you use. If you use them, it won't matter if you use M or NF.

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