gds-generation

name	gds-generation
description	Use when creating GDS layout files programmatically using KLayout's Python API (pya module). Covers cell creation, shape insertion, and file output.

GDS File Generation with KLayout Python API

Running KLayout Python Scripts

klayout -b -rm script.py                    # Run script in batch mode
klayout -b -rm script.py -- --arg1 val1     # With arguments (after --)

Minimal GDS Generator Template

import pya
import argparse

DBU_UM = 0.001  # Database unit: 1 nm

def um_to_dbu(um_val):
    """Convert micrometers to database units."""
    return round(um_val / DBU_UM)

def main():
    ly = pya.Layout()
    ly.dbu = DBU_UM
    top = ly.create_cell("TOP")

    # Define layers
    li_met1 = ly.layer(pya.LayerInfo(68, 20))   # Metal 1
    li_via  = ly.layer(pya.LayerInfo(68, 44))    # Via

    # Insert shapes (coordinates in DBU = nm)
    x0, y0 = um_to_dbu(0), um_to_dbu(0)
    x1, y1 = um_to_dbu(10), um_to_dbu(5)
    top.shapes(li_met1).insert(pya.Box(x0, y0, x1, y1))

    # Write output
    ly.write("output.gds")

if __name__ == "__main__":
    main()

Key Concepts

• Database unit (DBU): GDS coordinates are integers in DBU. With dbu = 0.001, 1 DBU = 1 nm.
• um_to_dbu(): Always convert micrometer design values to integer DBU before creating shapes.
• Layer info: pya.LayerInfo(layer_number, datatype) — see SKY130 layer reference.
• Shapes: Use pya.Box(x1, y1, x2, y2) for rectangles, pya.Polygon for arbitrary polygons.

Shape Types

# Rectangle (Box)
top.shapes(layer).insert(pya.Box(x0, y0, x1, y1))

# Polygon (arbitrary shape)
pts = [pya.Point(x0, y0), pya.Point(x1, y0), pya.Point(x1, y1), pya.Point(x0, y1)]
top.shapes(layer).insert(pya.Polygon(pts))

# Path (wire)
pts = [pya.Point(x0, y0), pya.Point(x1, y1)]
top.shapes(layer).insert(pya.Path(pts, width_dbu))

Generating Pass/Fail DRC Test Cases

For DRC testing, generate two sets of GDS files:

• Pass cases: Geometries that satisfy all design rules (sufficient spacing, width, etc.)
• Fail cases: Geometries that intentionally violate specific rules

def generate_pass_case(ly, top, layer, min_width_um, min_space_um):
    """Two rectangles with sufficient width and spacing."""
    w = um_to_dbu(min_width_um * 1.5)  # 50% margin
    s = um_to_dbu(min_space_um * 1.5)
    h = um_to_dbu(2.0)
    top.shapes(layer).insert(pya.Box(0, 0, w, h))
    top.shapes(layer).insert(pya.Box(w + s, 0, 2*w + s, h))

def generate_fail_case(ly, top, layer, min_width_um, min_space_um):
    """Two rectangles with insufficient spacing."""
    w = um_to_dbu(min_width_um * 1.5)
    s = um_to_dbu(min_space_um * 0.5)  # 50% of minimum = violation
    h = um_to_dbu(2.0)
    top.shapes(layer).insert(pya.Box(0, 0, w, h))
    top.shapes(layer).insert(pya.Box(w + s, 0, 2*w + s, h))

Common Mistakes

Mistake	Fix
Float coordinates	Always convert to int DBU with um_to_dbu()
Forgetting ly.dbu = DBU_UM	Set DBU before creating shapes
Using wrong layer numbers	Check SKY130 layer reference
Shapes at origin overlapping	Offset shapes to avoid unintended intersections