Properties and Applications

Indium tin oxide (ITO) is a mixture of indium oxide In₂O₃ and tin oxide SnO₂ with the total formula In_2-xSn_xO₃. Its share of tin may amount to up to 20 percent. Being semiconductive, it has a high electrical conductivity. Moreover, thin layers of about 200 nm are transparent in the area of visible light while infrared light is reflected. Indium tin oxide has a density of approximately 7 g/cm³ and a white to yellowish color. According to composition, it can take on other colors (blue, green, yellow, etc.). ITO is almost insoluble in water.

Indium tin oxide is one of the most important transparent, electrically conductive materials. In the optoelectronic industry, it is mainly used to coat semiconductor sensor wirings and manufacture diverse electro-optical components and devices such as liquid-crystal screens, organic light-emitting diodes (OLEDs), and touchscreens. In addition, it is used as transparent heating glass in de-icing systems, heatable object slides or hot states. Indium tin oxide is found in invisible antennae and thin-film solar cells. Indium tin oxide layers protect image sensors of high-quality digital cameras. Due to its transparency and electrical conductivity, ITO is used for coating non-conductive materials such as plastics to prevent electrostatic charging.

To increase the conductivity and IR reflectivity of the materials, indium tin oxide is added to transparent varnishes, adhesives, plastic films, and fibers in the form of fine to nanoscale particles (powders) of different compositions. Besides, one finds ITO powder coatings, and transparent ITO-based conductors that have been manufactured by means of special printing techniques.

It is due to the limited availability and high prices of indium that intensive efforts are made worldwide to replace indium tin oxide by other transparent and conductive materials.

Occurrence and Production

Indium tin oxide is a technical product. It can be applied to substrates, mainly to glass and plastic films, by means of different coating methods. High-vacuum sputtering is the most commonly used method. Although it reduces the coating area, it can ensure a high homogeneity of the coating layers. Larger surfaces can be coated through reactive thermal evaporation in air at temperatures above 300 °C or by means of the sol-gel technique.
Fine-grained to nanocrystalline powders are preferably obtained by co-precipitation from aqueous solutions: Soluble indium or tin components are precipitated through an increase in pH values. To obtain the desired properties, a thermal aftertreatment is carried out at temperatures above 300 °C.


Literature

1. Wikipedia „Indiumzinnoxid“ ( as of 22.03.2011)
2. Gunar Kaune: Röntgenografische Charakterisierung von Indium-Zinn-Oxid-Dünnschichten, Diplomarbeit, Fakultät für Naturwissenschaften, TU Chemnitz, 2005
3. Patents on the use and manufacturing of ITO powders: DE69818404T2 of 01.07.2004; Degussa DE102004041747A1 of 02.03.2006; Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V. DE10261541A1 of 01.07.2004