DEPOSITION

Four ways to lay down metal

Sputtering An argon plasma knocks atoms off a target.

Evaporation Atoms fly in straight lines: needed for junctions.

Hot or reactive Heated wafers and nitrogen gas change the film.

The deposition method shapes a film's crystal and its loss.

THE METALS

Four superconducting films

Aluminium The junctions.

Niobium and tantalum Pads, resonators and wiring.

TiN Ultra-low-loss resonators.

A transmon is usually made of two metals.

OXIDES

Native oxide Grows within minutes in air.

TLS defects Flipping atoms that absorb qubit energy.

Fixes Metals with benign oxides, or capping in vacuum.

A film's top few nanometres can matter more than the rest.

THICKNESS

Rate × time Thickness follows the tool's calibration.

100 to 200 nm A typical qubit film.

Calibration Measured with profilometers and X-rays.

Every fab recipe is numbers that someone measured.

CRYSTAL PHASE

Alpha Body-centred cubic, 4.4 K, low loss.

Beta Tetragonal, under 1 K, lossy.

Heat Hot sapphire gives alpha films.

The same element can make a great qubit or a poor one.

UNIT 22 STUDY COMPLETE

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You've met the deposition tools, compared four films, protected a surface from its oxide, hit a thickness target and grown alpha tantalum.