Please change the sky130 default decap cell to be sky130_ef_sc_hd__decap_40_12

[DavidRLindley]

The historical default sky130 decap cell has been sky130_ef_sc_hd__decap_12. Last year Skywater reduced the sky130 poly density range requirements and most PNR blocks started failing poly pattern density. As a band aid I think we changed out the decap cell to a smaller one there there were issues with that solution. In the latter half of 2024 we added new decap cells to the sky130_fd_sc_hd library as a permanent fix.

sky130_ef_sc_hd__decap_20_12
sky130_ef_sc_hd__decap_40_12
sky130_ef_sc_hd__decap_60_12
sky130_ef_sc_hd__decap_80_12

These cells are identical to sky130_ef_sc_hd__decap_12 except for the amount of poly in the cell (and a few licons that don't affect anything) . EG sky130_ef_sc_hd__decap_20_12 has 20% of the poly as does sky130_ef_sc_hd__decap_12. Based on experiments I determined that using the sky130_ef_sc_hd__decap__40_12 decap cell reduces the poly density into the high end of the acceptable range. Of course this is dependent on the actual circuit but will result in layout that will more likely pass poly density. Please change the sky130 default decap cell to be sky130_ef_sc_hd__decap_40_12.

[RTimothyEdwards]

@DavidRLindley : It sounds like you want a change to be made to the LibreLane configuration? You might want to consult with Donn or Leo and get a pull request made.

[mole99]

Yep, that's what he did: librelane/librelane#751

A PR would be appreciated, as it might take a while until we get to it since there's a lot going on currently.