Alternative to ITO
August 17, 2011, Emerging Display Technologies Conference, San Jose, CA—Rahul Gupta from Cambios talked about transparent conductors for displays. The drive for higher performance and resolution is driving the industry towards alternatives to ITO (indium tin oxide) for on-surface transparent conductors.
Transparent conductors are processed as a coating material, either some type of ink or applied on a film. One possible alternative to ITO is silver nano wires which exhibit very high conductivity of under 10 ohms per square. These conductors have high optical transmission of 98 percent at 30 ohms per square and neutral color with a B* of 0.7 and below. Resistance is a function of the nano wire density and there’s some interaction between resistance and the optical characteristics. In addition to higher transmission, the material is lower reflectivity than ITO as it is index matched to the substrate.
The conductors are can be solution processed at less than 120° C. The conductors can be transferred to the display cell and patterned with photolithography. One characteristic that is especially useful for flexible substrates is the material is not brittle like ITO, but has good flexibility. One result of all these characteristics is a higher contrast ratio for the display.
Current production capacity is 20 m of film per minute, which is about an order of magnitude faster than ITO. Total capacity is about 26 million square meters per year, approximately the world’s current volume for ITO. Application of the materials can use existing spin or slot coating equipment onto a film substrate, or is available as a paste for direct application.
Technology improvements include reducing the resistivity, reducing color cast from the materials, and reducing haze—light scattering from the conductors at the surface—through better index matching of the carrier materials and adhesives. These materials can be applied in existing capacitive touch displays, OLED, photovoltaic panels, and any other functions where a transparent conductor is required.
