Indium tin oxide

Indium tin oxide, usually called ITO, solves an odd problem: how do you put a wire right where light needs to pass? Metals are opaque, and most clear materials don't conduct. ITO does both. A thin film lets through roughly 85 to 90% of visible light while carrying current well.

It's a mix of about 90% indium oxide and 10% tin dioxide by weight. The two powders are blended, pressed and fired into dense ceramic tiles called sputtering targets. In a vacuum chamber, a plasma knocks atoms off the target, and they land as a thin, even film on the glass or chip below, often around 100 nanometers thick. Each tin atom that takes an indium atom's place in the crystal gives up a spare electron, and missing oxygen atoms add more. Those free electrons carry the current, while the oxide's wide band gap lets visible light pass straight through.

In the thin-film transistor array, ITO forms the clear electrode in every subpixel. On the color filter, it's a shared electrode across the front. In a blue LED chip, it spreads current across the top without blocking the light. Displays and touchscreens use roughly half of the world's indium this way.