PORTLAND, Ore. — Indium tin oxide (ITO) is the mainstay of the touchscreen industry, providing a transparent conductor behind the glass cover whose capacitance changes when touched. Unfortunately, indium is becoming rarer, increasing its price and setting off a worldwide search for alternatives.
Many possibilities have been offered -- from carbon nanotube coatings to inherently conductive polymers. However, none of these alternatives claims to offer 10 times the conductivity of ITO plus the ability to work on flexible surfaces. That's what Cima NanoTech of St. Paul, Minn., claims for its proprietary SANTE (self-assembling nanoparticle technology for electronics). In partnership with Saudi Basic Industries Corp. (SABIC), they developed the industry's first transparent conductive polycarbonate film using Cima Nanotech's SANTE nanoparticle technology and SABIC's transparent LEXAN film.
"Our ITO alternate is about 10x more conductive and can be deposited on a lot more substrates than ITO -- including transparent polycarbonate," Jon Brodd, CEO of Cima Nanotech, tells EE Times. "And because our resistivity is about 15 ohms per square, whereas ITO is 150 ohms per square, we can also handle much larger touch screens than ITO. For instance, our prototype is a 42-inch touchscreen that is running at about twice the speed of an iPad."
The bezel-less, 42-inch, 150 Hz, 10-point multi-touchscreen was created for the demo in partnership with Amdolla Group of Shenzhen, China -- whose customers have included Apple, Intel, Lenovo, Huawei, TCL, and many others. Amdolla is currently working on 55-inch and larger formats for Cima/SABIC. Cima/SABIC is also going after other applications ITO is used for today.
Silver web covers polymer in connected lines about five microns wide and three microns thick.
(Source: Cima NanoTech)
"We are also looking at transparent 'no-line' anti-fogging capabilities for automotive windows, better EMI shielding effectiveness for electronics, and transparent WiFi/Bluetooth antennas for mobile devices like smartphones, tablets, laptops, and all-in-one computers," says Brodd. Other applications include OLED lighting, electrochromic, and other flexible applications.
SANTE was created as a self-assembly method for micron-thin silver conductive networks, but also works with gold and other alloys. The trick to the technique is first to put the metal, here silver nanoparticles, in an emulsion -- a water-based solvent liquid, which is deposited over the whole surface of SABIC's Lexan polycarbonate.
Here comes the trick: Since the solvent evaporates faster than the water, the silver particles assemble around the evaporating droplets of water. So in about 20 seconds a continuous network is formed around the water droplets, leaving a moiré-less random honeycomb-like network of silver about 5 microns wide and 3 microns thick. A conventional oven then sinters the nano particles into the transparent polycarbonate.
Closeup of silver web of self-assembling nanowire web
on flexible, transparent substrate.
(Source: Cima NanoTech)
The resulting conductive polycarbonate films can be processed using an inexpensive roll-to-roll process that consumes only about a gram of silver per square meter. The finished Lexan polycarbonate is tolerant of flexing, stretching, torsion, and tension, making it suitable for self-service kiosks, interactive tabletops, widescreen interactive digital signage, interactive flat panel displays, and other applications that require large touch screens that respond quickly. The substrate can also be thermoformed into various curved and 3D form factors. Because the films are about 10x faster than ITO, Cima plans to sell the films as high-performance materials rather than low-cost materials.
"Our pricing will be competitive with ITO," Matt Gray, director of consumer electronics marketing for SABIC Innovative Plastics, told EE Times.
Cima NanoTech has development centers in the US, Singapore, Israel, Japan, Korea, Taiwan, and China.
— R. Colin Johnson, Advanced Technology Editor, EE Times