Datatype

A datatype is a second small number carried with a sheet in some factory files, so two kinds of marks can share one sheet name.

Graphic Design System II (GDSII) writes the pair, because the first number alone is not always enough. One sheet named “metal 1” might hold the real conducting shapes on datatype 0 and a comment outline on datatype 20. A mask shop that reads only the first number will treat the comment as metal, which is an expensive mistake. In the file the pair looks like 31/0 or 31/20: same sheet 31, two jobs. A 0.5 micrometer square on 31/0 might be a real cut. The same square on 31/20 might be a note that must never reach the photomask. The named sheet itself is a layer. Together, layer and datatype are how a stream file points at a bucket of geometry. A process kit, often called a PDK, publishes which pairs mean metal, holes, text, or keep-away marks. Datatype is not a thickness. It is a label, and thickness lives in the process recipe, not in that second integer.

The upper strap carries an extra end mark. The lower strap is the same metal without that mark.

How the pair is written, what a layer is for, and how GDSII stores both numbers are covered in GDS layer and datatype, what a layer is for, and GDSII in plain language.