Indium tin oxide

Indium tin oxide (ITO, or tin-doped indium oxide) is a mixture of indium(III) oxide (In₂O₃) and tin(IV) oxide (SnO₂), typically 90% In₂O₃, 10% SnO₂ by weight. It is transparent and colorless in thin layers. In bulk form, it is yellowish to grey.

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Indium tin oxide's main feature is the combination of electrical conductivity and optical transparency. However, a compromise has to be reached during film deposition, as high concentration of charge carriers will increase the material's conductivity, but decrease its transparency.

Thin films of indium tin oxide are most commonly deposited on surfaces by electron beam evaporation, physical vapor deposition, or a range of sputter deposition techniques.

Uses

ITO is mainly used to make transparent conductive coatings for liquid crystal displays, flat panel displays, plasma displays, touch panels, electronic ink applications, organic light-emitting diodes, and solar cells, and antistatic coatings and EMI shieldings. In organic light-emitting diodes, ITO is used as the anode (hole injection layer).

ITO has been used as a conductive material in the plastic electroluminescent lamp of toy Star Wars type lightsabers ^[1].

ITO is also used for various optical coatings, most notably infrared-reflecting coatings (hot mirrors) for architectural, automotive, and sodium vapor lamp glasses. Other uses include gas sensors, antireflection coatings, electrowetting on dielectrics, and Bragg reflectors for VCSEL lasers.

Reportedly, ITO is used as sensor coating in the Canon 400D/XTi and Sony Alpha DSLR-A100.

ITO thin film strain gauges can operate at temperatures up to 1400 °C and can be used in harsh environments, eg. gas turbines, jet engines, and rocket engines [1]

Alternatives

Due to high cost and limited supply of indium, the fragility and lack of flexibility of ITO layers, and the costly layer deposition requiring vacuum, alternatives are being sought. Carbon nanotube conductive coatings are a prospective replacement. These coatings are being developed by Eikos and Unidym as a lower cost, more mechanically robust alternative to ITO. PEDOT and PEDOT:PSS are manufactured by AGFA and H.C. Starck. PEDOT:PSS layers are in use (though they degrade when exposed to ultraviolet radiation and have other disadvantages). Other alternatives are eg. aluminium-doped zinc oxide. Cambrios, founded in 2002 by Drs. Angela Belcher of MIT and Evelyn Hu, has a wet-processable transparent conductive film alternative for ITO.

References