Material · Engineered

Indium tin oxide

A coating that conducts electricity and lets light through — the reason a touchscreen can be looked at as well as touched.

Electrical conductor Optical medium

Conducting electricity and transmitting visible light are close to mutually exclusive. Conduction needs free electrons, and free electrons absorb and reflect light — which is why metals are opaque and mirrors are metal. Indium tin oxide is one of a small number of materials that manage both, by being a wide-band-gap semiconductor doped heavily enough to conduct while its gap remains too wide for visible photons to excite.

Every capacitive touchscreen has a patterned layer of it. So does every LCD panel and most flat-panel displays, and the transparent electrode is the part of the device that makes the rest possible.

Economic significance

ITO is where most of the world's indium goes, and indium is a by-product of zinc — dispersed, never mined for itself, and produced in a few hundred tonnes a year worldwide. A display industry that ships billions of units a year therefore rests on a metal whose supply cannot respond to its demand.

That has driven a long search for a replacement — silver nanowire meshes, carbon nanotubes, graphene, conductive polymers — and none has displaced it. The recurring problem is not conductivity or transparency individually but achieving both while being manufacturable at square kilometres a year.

It is also brittle, which is the specific obstacle to genuinely foldable displays: a ceramic film cracks where a plastic substrate bends.

Medium confidence Weak evidence

How we know: checked recently · only one source, so there is nothing to cross-check it against · stated directly by the source.

How this connects

Where a connection has been confirmed by an outside reference, that reference is named beside it.

contains

Indium — element · the bulk of it, and where most of the world's indium goes Wikidata
Tin — element · the dopant, at perhaps a tenth of the indium — it is what supplies the free electrons that make the film conduct Wikidata
Oxygen — element · the other half of both oxides, and the reason the material is transparent at all: it is a wide-band-gap oxide, doped until it conducts Wikidata

is used in

Semiconductor manufacturing — industry · as the transparent electrode of every flat panel display and capacitive touchscreen
Electronics manufacture — industry · the transparent conductor of every touchscreen, and one of the clearest single-material supply dependencies there is
Smartphone — object · the transparent electrode of the touchscreen, which has to conduct and be invisible at the same time — a combination almost nothing offers

is produced by

Vapour deposition — process · sputtered onto glass in sheets, which is the only way to make a transparent electrode over square metres

Sources

Wikidata
Wikimedia Foundation · Creative Commons CC0 1.0 Universal (public domain dedication)
Material World
Our own writing

Where it comes from, and what it becomes

Follow Indium tin oxide back to what it starts as, and forward into what it becomes. Each step is a documented one — a real route material takes, not a chain of inference.

Upstream — what it comes from

Indium tin oxide → is produced by (sputtered onto glass in sheets, which is the only way to make a transparent electrode over square metres) → Vapour deposition

Downstream — what it becomes

Indium tin oxide → is used in (the transparent electrode of the touchscreen, which has to conduct and be invisible at the same time — a combination almost nothing offers) → Smartphone → is used in (and it is where four separate raw-material arguments meet — the 3TG conflict minerals, cobalt, the rare earths, and everything too dispersed to recover) → Electronics manufacture → is associated with (and the supply chain it produced is the deepest and most concentrated in the world economy) → The semiconductor era complete chain
Indium tin oxide → is used in (the transparent conductor of every touchscreen, and one of the clearest single-material supply dependencies there is) → Electronics manufacture → is associated with (and the supply chain it produced is the deepest and most concentrated in the world economy) → The semiconductor era complete chain
Indium tin oxide → is used in (as the transparent electrode of every flat panel display and capacitive touchscreen) → Semiconductor manufacturing
Indium tin oxide → is used in (the transparent electrode of the touchscreen, which has to conduct and be invisible at the same time — a combination almost nothing offers) → Smartphone → is associated with (the object the whole period arrives at, and the one that put roughly sixty elements into a pocket) → The semiconductor era complete chain
Indium tin oxide → is used in (the transparent electrode of the touchscreen, which has to conduct and be invisible at the same time — a combination almost nothing offers) → Smartphone → is used as (and the radio front end alone reaches gallium arsenide, gallium nitride and a dozen filters made of piezoelectric ceramic) → Telecommunications