foundry fabrication (300 mm / CMOS)

Foundry fabrication means building qubit chips on the same big, automated production lines that make the processors in laptops and phones, instead of in a small university cleanroom. A modern foundry works on round silicon wafers 300 millimeters across, about the size of a dinner plate, and patterns thousands of dies on each one with machines that repeat the same step identically all day long. The dream is simple: if the chip industry can already print billions of near-identical transistors with astonishing precision, maybe that same discipline can print qubits that actually come out the same as each other and in large numbers.

The advantage is process control and scale. A foundry holds temperature, film thickness, and feature size to tight, monitored tolerances, tracks every wafer through statistics, and runs the same recipe across a whole 300 mm wafer, so a good result on one chip is far more likely to repeat on the next. This uniformity matters most for spin qubits, which are tiny and built from silicon and silicon-germanium that foundries already handle. It also lets you make many test chips quickly and learn from data rather than from one hand-built device at a time, which is how the rest of the chip world improves so steadily.

The honest catch is that a standard CMOS line was tuned to make transistors switch fast, not to keep a quantum state alive. Many ordinary foundry materials and steps quietly leak qubit energy: the wrong metals, oxides, surface residues, or thermal steps that would never bother a logic chip can wreck coherence. So adapting a foundry means swapping in low-loss materials, cleaner interfaces, and gentler processing while keeping the line's discipline intact. It is real and progressing, with both spin-qubit and superconducting devices now coming out of 300 mm lines, but matching the best lab-made qubits at industrial uniformity is still an open, in-progress effort.