What is a PDK (Process Design Kit)?

A Process Design Kit (PDK) is a collection of files, models, and design rules provided by a semiconductor foundry (like TSMC, SilTerra, Tower etc.) to enable photonics designers to design photonic or electronic circuits that can actually be fabricated in the foundry’s specific process.

In silicon photonics, a PDK ensures that your photonic devices — waveguides, couplers, modulators, detectors — are manufacturable using the foundry’s standardized fabrication processes.

What’s inside a Silicon Photonics PDK?

A good photonics PDK typically includes:

Component	Description
GDSII Layout Cells	Pre-made building blocks (like waveguides, grating couplers, MMI splitters) you can place in your design.
Design Rules (DRC)	Set of rules defining minimum spacing, width, layer usage — to ensure designs can be fabricated reliably.
Process Layer Stack	Defines all the material layers (Si, SiO2, SiN, metals) and their thicknesses, refractive indices, etc.
Compact Models (CML)	Behavioral models for simulators (like Lumerical INTERCONNECT) that represent device performance (loss, phase shift, etc.).
SPICE Models	Electrical models for photonic-electronic co-simulation (for photodetectors, heaters, etc.).
Example Designs	Pre-made photonic circuits (like MZI interferometers or ring resonators) to help you get started.
Scripting Interfaces	Python/Skill scripts for automating layout generation or analysis.

Why is a PDK Important?

• Guarantees Manufacturability: Ensures your design complies with the foundry’s process limits.
• Accelerates Design: You can focus on system design rather than building every component from scratch.
• Enables Simulation: You can simulate your circuit’s performance before tape-out using the pre-calibrated models.
• Reduces Risk: Foundry-validated building blocks improve first-pass success rates.

Example

If you’re designing a silicon photonic transceiver, the PDK might provide:

• Standard single-mode waveguides (500 nm wide)
• Bend radius limits to avoid excessive loss
• Pre-characterized grating couplers (for fiber-to-chip coupling)
• Power splitters
• Models for thermo-phase shifters
• Models for Mach-Zehnder modulators (MZM)

You just assemble these building blocks, run simulations, and your design is ready for tape-out.

Analogy

A PDK is like a LEGO set — it gives you all the bricks (devices), blueprints (rules), and tools (models) to build a functioning photonic chip.