DEPOSITION

Building films atom by atom

PVD · CVD · ALD

Deposition tools lay down thin films. Sputtering and evaporation release material from a source onto the substrate. Chemical vapor deposition (CVD) grows films from reacting gases. Atomic layer deposition (ALD) adds one atomic layer per cycle. They make current collectors, oxide layers, and conformal coatings.

The same deposition tools as MEMS, aimed at energy storage.

WHAT EACH BRINGS

Choosing a deposition method

Sputtering, evaporation Metal current collectors and thin oxide or nitride films

CVD Graphene, nanotube forests, and diamond-like films

ALD Ultra-thin, even coatings on 3D structures, even inside pores

The catch Vacuum equipment, slow rates, and high cost per area

ALD and CVD can coat 3D scaffolds where line-of-sight methods can't.

LIFT-OFF

Patterning without etching

resist → metal → lift

For metals that are hard to etch, pattern the resist first, deposit metal over everything, then dissolve the resist. The metal sitting on the resist lifts away, and only the metal that touched the substrate remains. It's a common way to make thin-film current collectors, such as interleaved gold fingers.

Pattern the negative space, then let the resist carry the excess away.

ETCHING

Carving out surface area

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Wet etching

A chemical bath removes material. Cheap and simple, but it usually cuts sideways too

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Plasma etching (RIE)

Ions and reactive gas remove material with much more directional control

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Deep RIE (DRIE)

Cuts tall, near-vertical trenches and pillars deep into silicon

Etching can turn flat silicon into towers, trenches, or pores, which are then coated with storage material.

TEMPLATES

Let a template set the geometry

aluminum → nanopores

Anodizing aluminum in acid grows a regular honeycomb of nanoscale pores, called anodic aluminum oxide. Filling those pores with carbon or a conductor, or anodizing titanium into an array of nanotubes, gives ordered, high-area electrodes without lithography.

The template sets the geometry; the coating sets the chemistry.

UNIT 33 STUDY COMPLETE

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Ready for the Fab Challenge?

You've covered thin films, lift-off, deep etching, and anodized templates.