Nanowire and Nanotube Touch Sensors

By Raverstead

Nanowire and carbon nanotube transparent conductive film (TCF) touch sensors were also on the agenda at the event. Sri Peruvemba, representing Cambrios, presented on the firm’s silver nanowire ink products of which Geoff Walker had remarked in his Touch Tutorial, “Cambrios is the first-mover and clear leader“ and “other suppliers (of silver nanowires) include Carestream, Blue Nano, Poly IC, etc”.

Sri Peruvemba began his presentation with a discussion of the various types of ITO-alternative materials that can be employed as transparent conductors and compared their characteristics, strengths and weaknesses before going on to focus on the properties of silver nanowires for TCFs. Peruvemba next discussed touch sensor trends and their applications in products including monitors, all-in-one computers, smartphones, tablets and eReaders. In October 2014 Cambrios announced its fifth generation silver nanowire ink products that can provide decreased sheet resistance and decreased optical haze.

Peruvemba ended his presentation with the conclusion that silver nanowire TCFs will lead in flexible and wearable product applications, owing in part to their ability to withstand more than 100K bend cycles at a 3 mm bend radius and because the firm’s latest generation silver nanowire ink can deliver lower sheet resistance and reduced haze.

Bob Senior of Canatu presented at TGM 2014 on High Contrast Flexible and Formable Touch. He concentrated the first part of his talk on the current market interest in wearable consumer electronic products. He pointed out that flexible displays and flexible touch sensors are not yet ready for mass production and application, but that for near term future products, touch is needed on 3D shapes and on flexible bands and displays.

During Senior’s presentation and at the Canatu TGM 2014 tabletop demo, he showed a 3D-shaped transparent sensor demonstrator incorporating the firm’s carbon nanobud (CNB) flexible TCF. The demonstrator was fabricated with complex shapes using industry standard film insert mold processes in a test mold with sharp edges, deep stretch to a depth of 7 mm at a diameter of 38 mm, and with 90 degree bending at a bending radius as small as 1 mm.

The most interesting property of the Canatu 3D-shaped demonstrator was the fact that the CNB film could be stretched locally by as much as 120% while still retaining its conductive properties. In speaking to Senior, he told me that the CNB TCF could be stretched because the individual CNB strands “slide” over each other and retain electrical continuity when the material is stretched during molding and forming. Another interesting characteristic of the CNB TCF is that the optical haze value does not increase as film sheet resistance is reduced to as low as about 60 ohms per square. As these developments in nanowire and nanotube TCFs reported at TGM2014 illustrate, incumbent indium tin oxide suppliers are very likely to experience continuing competitive challenges from developers of new alternatives. – Phil Wright