How indium tin oxide coatings are made

Mix the two powders

Indium oxide and tin oxide powders are blended, in patent examples at weight ratios of 95:5 and 90:10. Ball mills are one tool for the job. Getting the two oxides to react fully avoids unwanted phases that disturb coating later.

Press a green compact

The powder is press-molded into a plate at ordinary temperature. This fragile block, called a green compact, holds its shape until the furnace.

Sinter the plate hard

These oxides resist sintering. In ordinary air firing, the plate reaches only about 60 to 70% of theoretical density, and a low-density target sputters slowly and sheds dust. Hot pressing reaches about 94% but costs far more, and one patent uses pressurized oxygen instead.

1,250 to 1,650 °C

Grind and cut the target

In one patent's examples, a surface grinder flattens the sintered body and a diamond cutter trims its sides. The finished piece is the source of atoms for the coating machine.

Sputter onto glass

In a vacuum chamber, inert gas ions strike the target and knock material onto the glass as a thin film. Sputtering won out because it covers large areas and repeats well. Electron beam evaporation is another route.

Balance clarity and conductivity

Thicker films carry more current but pass less light, so every coating is a compromise. A thin film can transmit more than 80% of visible light.

Etch fine patterns

Photoresist masks the film, and etching cuts it into precise lines and pads. These become the transparent wiring of a display or touch panel. Precise etching is the main edge this material holds over aluminum-doped zinc oxide in LCDs.