min_region_density

For each connected region of a base layer that’s big enough to matter, the fraction of its area covered by a feature layer must be at least value (%).

Semantics

Unlike min_density and min_windowed_density, which measure a chip-wide or per-window percentage, this measures density per connected region of the base layer — each qualifying region gets its own pass/fail, so a single starved region can’t be averaged out by well-covered neighbours elsewhere on the chip.

“Big enough to matter” means at least min_size µm across in every direction, found by a tiled erosion of radius min_size / 2 (MergedCache::plate_regions): a region that fully vanishes under that erosion has no spot wide enough to qualify and is skipped entirely, regardless of its total area (a long, thin sliver never trips this rule, no matter how large). Both the base and feature layers stay on the cache’s tiled representation throughout — a large metal plate is never globally unioned.

For each region that is wide enough, the check compares the feature layer’s enclosed area against the base region’s true filled area (not its bounding box) and reports a violation if the ratio falls short.

Layers

Two layers, positional:

1. Base layer — the region a percentage is measured over (e.g. a large metal plate).

2. Feature layer — the layer whose coverage inside each base region is measured (e.g. metal slits).

Parameters

min_size

The minimum span (µm) a base region’s widest spot must have to be checked at all. Defaults to 35.0.

Violation markers

One point marker per undersized region, at a point that always lands on the region’s “wide” spot (not just anywhere in its bounding box).

KLayout equivalent

Not a single built-in operator — mirrors a hand-rolled per-plate density measurement (as used for slit-density rules like IHP’s Slt.i): find wide plates via a sized/unsized erosion round-trip, then measure feature coverage inside each one individually rather than as one chip-wide ratio.

Example

- id: Slt.i
  check: min_region_density
  layers: [Metal1NoExempt, Metal1.slit]
  value: 6.00
  params:
    min_size: 35.0