Analysis Nikkei Electronics Asia -- October 2009
Transparent Electrode Materials Replacing ITO

From liquid crystal display (LCD) panels and touch panels to electronic paper (e-paper), solar cells and more, indium tin oxide (ITO) is extensively used as the material for transparent electrodes. New transparent electrode materials are reaching the level of practical use now, though, and will replace ITO thanks to characteristics including improved bending, lower cost and higher transmittance. Already these new materials are entering use in touch panels, and e-paper will follow suit shortly. In the near future, the trend may spread to applications such as solar cells and LCD panels, too. 

ITO is widely used as the material for transparent electrodes in a diverse range of electronic devices including LCD panels, plasma display panels (PDP), touch panels, e-paper, solar cells and organic electroluminescent (EL) panels. In some of these applications, however, new transparent electrode materials are beginning to replace ITO. 

Bridgestone Corp of Japan, for example, has prototyped an e-paper using a conductive polymer for transparent electrodes instead of ITO, as announced in June 2009. A source at the firm explains they wanted to use printing technology to make a thin, light, flexible e-paper at low cost, but were unable to use ITO because of breakage when bent. It was also impossible to manufacture ITO electrodes using printing technology. In response, the firm tried making new transparent electrode films that could be applied using printing technology, and which could be bent. "Performance is still not satisfactory, but we expect it will reach the commercial level in two years. We want to commercialize it as soon as possible," commented the company.

Adoption in Touch Panels

While there have been no official announcements yet, new materials are already being adopted in transparent electrodes in some products. According to materials manufacturer TDK Corp of Japan, its "FLECLEAR" ITO film (a film applied by coating) has already been used in some touch panel products.

The replacement of ITO in touch panels seems likely to proceed rapidly. Major touch panel manufacturer Nissha Printing Co Ltd of Japan plans to use conductive transparent ink with minute Ag wires mixed in (Ag wire ink) as the transparent electrode material for projected capacitive type touch panels. The actual adoption data has not been disclosed, but the company has begun collaborative development of Ag wire ink with Cambrios Technologies Corp of the US, a tech start-up.

Nissha Printing has several reasons for switching to a new material: first, manufacturing a low-cost, colorless touch panel providing better color fidelity for the displayed image. The ITO film used on touch panels now is slightly yellow, while the new material is almost completely colorless. While conventional ITO requires a vacuum process for manufacturing, Ag wire ink films can be coated on, which could mean lower manufacturing costs.

Another reason is to make possible three-dimensional (3D) touch panels, which can be mounted on curved surfaces. Conventional ITO has poor flexibility, but Ag wire ink bends easily.

Alps Electric Co Ltd of Japan is also considering replacing ITO in its touch panels, with ZnO-based transparent electrodes, and is currently at the research and development (R&D) stage. ZnO offers excellent transmittance to short-wavelength light, unlike ITO, which improves image appearance. The company also appears to be interested in superior performance in bending and other characteristics, in the same way as Bridgestone, Nissha Printing and others.

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