Layout "CuPillarPad" from sg13g2_pr violates grid design rules

[RTimothyEdwards]

The layout "CuPillarPad" in libs.ref/sg13g2_pr/gds/sg13g2_pr.gds violates grid rules by having a circular pattern on TopMetal2 in contravention of the Grid Rule: "Following layers are only allowed on 90, 135, 180, 225, and 270 degree angles: GatPoly, Activ, Metal1, Metal2, Metal3, Metal4, Metal5, TopMetal1, TopMetal2".

The design rule document does not reference the "pillar" layer (GDS layer 41:35) and it is not clear that it is supported, although it appears in the example layouts in sg13g2_pr.gds. There are no DRC rules regarding the pillar layer.

Presumably it would be a valid layout to place a pillar in the middle of a (legal) octagonal TopMetal2 area. But if this is supposed to be a legal layout, then the grid rule is wrong.

[sergeiandreyev]

Hi @stefansimon42, could you please take a look?

[sergeiandreyev]

and regarding the CuPillarPad layout itself - we're now reviewing it, it seems an update is upcoming

[mole99]

Please see also issue #412, in which we came to the conclusion that I could use non-45° angles on TopMetal2 (in my case for the logo of Greyhound).

[RTimothyEdwards]

@mole99 : Yes, but that was basically a waiver. I prefer to have unrestricted angles on metal myself, but that's for the foundry to decide. If rounded or curved shapes are acceptable, then the rule should not exist. Otherwise, if it's only a "don't care" condition for logos and specific structures like CuPillarPad, then those can be specifically called out in the DRC. Some foundries have a "logo ID" layer that prevents non-essential DRC from being run on logo areas. In this case, though, my argument would be that the structure has been drawn unnecessarily with the outer TopMetal2 edge being circular. Only the (circular) pillar in the center is relevant to the CuPillarPad device. The TopMetal2 shape surrounding it could just as easily be a square or an octagon.

[mole99]

I'm not sure if it was a waiver or if the rule should not exist. I haven't got a definite answer in my issue. I would prefer unrestricted angles too. Besides, I think they are necessary for RF designs, aren't they?

I understand now what you refer to in this issue. Only the copper pillar has to be circular.
Attaching this image for reference:

[sergeiandreyev]

for any circular shape inside one of our standard PDK devices the angle and offgrid rule checks should not exist / run - and this has to be fixed in our DRC decks (both opensource and proprietary), additionally we have to update DRM to have this written explicitly and as clear as possible (and any device-specific waivers, if applicable, should be listed in full)
how it should work for the user developed designs (+ all layers, combinations), remains to be discussed

[sergeiandreyev]

The TopMetal2 shape surrounding it could just as easily be a square or an octagon.

yes, we have these combinations parameterized in advanced pad Pcell (which is not yet part of the OpenPDK though)