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Factory Functions

A factory in kfactory is a function that returns another function — a cell-making function bound to a specific KCLayout. Factories are the recommended way to build production PDKs because they:

• Tie cells to a specific layout — every cell built by the factory lives in the same KCLayout, so layer indices are consistent.
• Cache automatically — the returned function is decorated with @kcl.cell, so repeated calls with the same arguments return the same cell object.
• Carry typed protocols — each factory returns a typed Protocol callable, so IDEs and type-checkers can validate arguments at the call site.
• Enable routing — the built-in routers (route_bundle, place_manhattan) require factory functions, not raw cells, so they can create bend/straight geometry on demand.

Available factories

Factories and routing

The built-in optical router (kf.routing.optical.route_bundle) requires factory callables — it uses them to instantiate bends and straights while building a route. Passing cells directly is not supported.

routes = kf.routing.optical.route_bundle(
    c,
    start_ports=[...],
    end_ports=[...],
    bend90_cell=bend_euler,      # factory callable
    straight_factory=straight,   # factory callable
)

Because each factory is bound to a KCLayout, all route geometry automatically lands in the correct layout and uses the correct layer indices.

Bundling factories in a PDK module

The recommended pattern for a production PDK is to define all factories in one place and import them wherever routing or assembly is needed:

# my_pdk/factories.py
import kfactory as kf
from kfactory.factories.straight import straight_dbu_factory
from kfactory.factories.euler import bend_euler_factory
from kfactory.factories.taper import taper_factory
from my_pdk.layers import LAYER

pdk = kf.KCLayout("MY_PDK", infos=LAYER)

straight = straight_dbu_factory(pdk)
bend_euler = bend_euler_factory(pdk)
taper = taper_factory(pdk)

__all__ = ["pdk", "straight", "bend_euler", "taper"]

Key rules

• straight_dbu_factory / taper_factory — arguments in DBU
• bend_euler_factory / bend_circular_factory — width and radius in µm
• Always bind the factory to the same KCLayout that owns the cells being routed

See Also