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#analog-design
Title
# analog-design
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Boris Murmann

05/06/2021, 4:34 PM
@User Do you know what substrate type the Google runs use (epi versus non-epi)? It makes a difference for the analog folks in terms of guard ring strategy. From the SkyWater website, it seems that they offer all options, but I don't know which one is used for the upcoming runs. https://www.skywatertechnology.com/technology/mixed-signal-asic/
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Tim Edwards

05/06/2021, 4:41 PM
I'm unable to find any information in the SkyWater documenatation stating whether the wafer is epi or non-epi. Would there be a parameter (i.e., SPICE model parameter) that would make this obvious? Otherwise I'll just ask somebody at SkyWater.
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Boris Murmann

05/06/2021, 4:54 PM
The spice models are not affected by this, so it would be great if you can ask. Thanks!
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Amro Tork

05/06/2021, 9:47 PM
Dr. Murmann, I was wondering what is deriving this question, Quality of the silicon layer an possible variation on the device parameters?
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Boris Murmann

05/06/2021, 10:24 PM
As I wrote, it has to do with how one deploys guard rings. For an epi-substrate, it is counterproductive to densely sprinkle p+ substrate tabs everywhere, while these are desired in the non-epi case for substrate noise suppression. This is covered in the literature, see e.g. https://ieeexplore.ieee.org/stamp/stamp.jsp?arnumber=210024
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Amro Tork

05/06/2021, 10:32 PM
Dr. @Boris Murmann, Aren’t you worried sir about the Latchup even in the case of epi? I didn’t check the DRC if it includes LU checks.
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Boris Murmann

05/06/2021, 10:33 PM
No.
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1
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Amro Tork

05/06/2021, 10:35 PM
Seems there is no rules.
For LU
Thanks Sir
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Tim Edwards

05/07/2021, 12:49 AM
@Amro Tork: There is a latchup rule set; the latchup rules are 15um distance between tap contact and edge of related diffusion, with a secondary rule of 6um distance if the area is within 50um of the padframe cells.
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Amro Tork

05/07/2021, 10:40 AM
@Tim Edwards I searched the Skywaters Readthedocs. But my basic search didn’t get that one. Could you please share the rule name/number?
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Boris Murmann

05/13/2021, 3:26 AM
@Tim Edwards Just wondering if you've been able to find out about the substrate type from SkyWater (non-ep versus epi)? Thanks!