N EARLY ALL DISPLAY DEVICES, including TFT-LCDs, OLEDs, and e-paper, contain one or more layers of a transparent conductive material, most commonly indium tin oxide (ITO). Currently, virtually all appli- cations of ITO for transparent conductors require deposition by a sputtering method in a vacuum chamber. Due to the significant growth of large-area displays, smart phones, and tablet devices that often incorporate projected-capacitive touch sensors, the market for the ITO sputtering targets has become several billion dollars as of 2011, with steady growth expected in the next 10 years. 1 If one considers not just the material cost of ITO, but also the deposition and patterning costs that are necessary to make display devices, it is reasonable to assume that the worldwide cost for creating a useful ITO layer is a significant multiple of the cost of the ITO sputtering targets. While the need for high-quality transparent conductive materials has grown dramatically, desirable alternatives to ITO have not emerged in the marketplace. Drawbacks of ITO and Potential Alternatives There are many factors driving the need for an ITO replacement material from the standpoint of raw-material supply, cost of ownership, and overall performance. Within the last 10 years, the price of ITO has been highly volatile, driven both by the increased consumption of the material as well as the geopolitically sensitive nature of the indium supply chain. 1 In addition to the high cost of the raw materials, capital investments for the vacuum-sputtering equipment necessary to deposit ITO are multiples of the cost of wet-coating tools with equivalent coating capacity. In addition, there are certain performance attributes of ITO that are undesirable, such as its brittle- ness and tendency to crack – a key factor with regard to making displays on flexible substrates. ITO also has a high refractive index that results in poor light transmission and the need for additional index-matching layers to achieve acceptable optical perfor- mance. Finally, high-temperature deposition conditions coupled with post-deposition annealing processes cause significant issues with achieving acceptable optical and electrical properties on plastic films. In addition to current applications that require high-quality transparent electrodes, emerging applications such as OLED lighting, thin-film photovoltaics, and new types of flexible displays require a higher-performing transparent electrode, driven by both cost and performance. Wet-processed alternatives such as carbon nanotubes and conductive polymers have not been competitive with the optical and electrical properties established by ITO. Graphene has been widely discussed as an alternative; however, its development is in its infancy. 2 In this article, the transparent conductive material produced by the author’s company, Cambrios Technologies Corporation, will be described as the first commercially available wet-processed alternative to ITO. Smart phones incorporating ClearOhm* materials have been mass produced since early 2011. 3.4 Silver Nanowire Technology ClearOhm conductive material consists of a wet-processable dispersion of high-aspect- ratio silver nanowires. Starting from silver salts, twinned-crystal silver nanowires are grown via the polyol process, a patented method 5 described by Xia. 6 By carefully controlling the process parameters, high- aspect-ratio silver nanowires can be synthe- sized at high yield, with an average diameter in the low tens of nanometers and an average length in excess of 10 μm. Independent control of nanowire length and diameter is possible, allowing the tailoring of morphology- dependent optical and electrical properties for specific applications. These nanostructures are then purified and formulated into a coatable suspension that is compatible with industry- standard coating methods such as roll-to-roll slot die coating or spin coating. The transparent conductive layer is created by coating the formulated suspension of nanowires on the surface of a substrate such Wet-Processable Transparent Conductive Materials A novel wet-processable transparent electrode material exhibits significant performance advantages over ITO. This material has recently achieved mass production in smart phones. by Michael Spaid Michael Spaid serves as Vice President of Product Development at Cambrios, where he is responsible for all product development and manufacturing development activities. Prior to joining Cambrios, he served as the Director of Microfluidics Engineering at Caliper Life Sciences, where he directed a core-technology R&D group responsible for conceiving and designing microfluidic chips used for bio- chemical, proteomic, and genomic analysis. He can be reached at mspaid@cambrios.com. 10 Information Display 1/12 0362-0972/01/2012-010$1.00 + .00 © SID 2012 frontline technology