KLayout Notes

Layer numbers: layer/datatype

A layer shown as poly.drawing - 66/20 has two parts:

• poly.drawing: a human-readable name.
• 66/20: the GDS layer number (66) and the datatype (20).

GDS files don't store layer names, only these integer pairs. Every shape in a GDS file carries a layer number and a datatype, and the PDK defines what each pair means.

• Layer number: which mask layer the shape belongs to (66 = poly, 67 = li1, 68 = met1, …).
• Datatype: what kind of shape it is on that layer. This is the part after the dot in the name.

Datatypes (purposes)

The same physical layer carries several kinds of shapes. For met1 (layer 68):

Name	Pair	Meaning
met1.drawing	68/20	The metal geometry that is actually manufactured
met1.pin	68/16	Marks pin locations, for LVS and routing
met1.label	68/5	Text labels naming nets
met1.net	68/23	Net-highlighting shapes
met1.res	68/13	Marks a metal resistor
met1.blockage	68/10	"Don't route here" areas for place-and-route
met1.boundary	68/4	Cell boundary on this layer

So met1.drawing and met1.pin are both metal 1. The first becomes metal on the chip; the second is bookkeeping for the design tools.

Where the names come from

The names come from a layer properties file (.lyp), an XML file that maps each pair to a name, color, and fill pattern:

<properties>
  <fill-color>#ff0000</fill-color>
  <name>poly.drawing - 66/20</name>
  <source>66/20@1</source>
</properties>

<source> is the pair to match (@1 means the first loaded layout) and <name> is the label shown in the layer panel. Without a .lyp, KLayout shows only the raw pairs (66/20).

For sky130 the file ships with the PDK at $PDK_ROOT/sky130A/libs.tech/klayout/tech/sky130A.lyp; this site uses a copy in gds/. To rename layers or change colors, edit the XML or adjust the layer panel in KLayout and use File → Save Layer Properties.

sky130 drawing layers

From sky130A.lyp, bottom of the stack to top:

Layer	Pair	What it is
nwell	64/20	N-well (body of PMOS devices)
diff	65/20	Active area: transistor source/drain
tap	65/44	Active area for well/substrate ties
nsdm	93/44	N+ source/drain implant
psdm	94/20	P+ source/drain implant
poly	66/20	Polysilicon (gates)
npc	95/20	Nitride poly cut (under poly contacts)
licon1	66/44	Contact: diff/tap/poly to li1
li1	67/20	Local interconnect
mcon	67/44	Contact: li1 to met1
met1	68/20	Metal 1
via	68/44	Via: met1 to met2
met2	69/20	Metal 2
via2	69/44	Via: met2 to met3
met3	70/20	Metal 3
capm	89/44	MiM capacitor plate (over met3)
via3	70/44	Via: met3 to met4
met4	71/20	Metal 4
via4	71/44	Via: met4 to met5
met5	72/20	Metal 5
pad	76/20	Passivation opening over bond pads

sky130 conventions worth knowing

• Contacts and vias share the number of the layer they sit on, with datatype 44: licon1 is 66/44 (poly is 66/20), mcon is 67/44 (li1 is 67/20), via is 68/44 (met1 is 68/20). The datatype is what tells them apart.
• "drawing" isn't always datatype 20. Contacts, vias, tap (65/44), and nsdm (93/44) use 44 for their drawn shapes.
• Don't confuse layer numbers across PDKs. 66/20 is poly in sky130 but can mean something else entirely in another process; always go through the PDK's .lyp or layer map.