From smart phones to tablets to GPS systems, touchscreen devices are everywhere. Consumers now expect an intuitive touch experience from every new device that hits the market. Since the introduction of Apple’s iPhone in 2007, the touchscreen sensor and IC market has exploded. In fact, according to NPD DisplaySearch, this market crossed $10 billion in 2011 and is expected to double again by 2014.
Touchscreens are set to become even more pervasive with the introduction of Windows 8, which integrates touch functionality into the world’s most widely used operating system. As such, the computer industry is gearing up to integrate touchscreens into thin touch-enabled laptops dubbed “ultrabooks” by Intel, in addition to all-in-one computers. Microsoft and Intel have also gone well beyond just developing their core products and are using hundreds of millions of dollars in marketing funds to ensure there is ample capacity for touchscreens for the new devices that use their products.
Already OEMs are creating very large touchscreen prototypes similar to those in the 2002 movie Minority Report, while others are completely transforming touchscreen functionality by making devices flexible and foldable. Unfortunately, the traditional transparent conductive materials are hindering production and keeping these innovations from reaching an eager group of consumers.
ITO: An Outdated Approach
The emerging markets for projected capacitive large area and flexible touchscreens require transparent conductor materials that combine low material and processing costs with flexibility, high conductivity, and excellent optical performance.
The vast majority of today’s touchscreen devices, such as smart phones and tablets, run on one such transparent conductive material: indium tin oxide (ITO) deposited on either plastic films or glass.
ITO is a ceramic material processed using vacuum deposition at high temperatures, making production very expensive. Developers have understandably turned to ITO on glass for larger area touchscreens since it offers low resistance. However, this option is far from ideal in several respects. In addition to being expensive, glass substrates are fragile and are thick and heavy.
For flexible or curved screens that require thin plastic substrates, electrical and optical performance diminishes significantly as the substrate materials limit the ITO deposition temperature. Also, ITO cannot withstand repeated bending or rolling as it is brittle and prone to cracking, limiting truly flexible devices.
In addition to concerns about its limited capabilities, there is an ongoing global push to replace ITO because of sustainability and price concerns. ITO is mostly indium, a rare, volatile, and geopolitically sensitive material. Most of the world’s indium is a byproduct of zinc mined in China, which has shown a willingness to use its mineral wealth as a competitive advantage for its own industries. According to Indium Corp., commissioning a new mine to produce zinc and indium takes seven years, and a sudden increase in demand is always followed by a period of shortage coupled with high prices. To meet the huge sudden increase in demand for touchscreens, an alternate transparent conducting material is not only desirable, but a necessity.
Forging Ahead With Alternative Materials
Some may view the transition away from ITO as a challenge, but several new conductive materials are poised to take over and enable exciting new devices.
One such material is graphene, a two-dimensional sheet of carbon that is a single atom thick with excellent strength, flexibility, transparency, and electrical conductivity. This new wonder material is a hot field for research. However, it is expected to take several years before there is a mature production process and compatible supply chain place.
Roll-to-roll metal mesh technology offers another alternative to ITO as low resistance can be achieved even on plastics substrates. Suggested applications of this technology include “edgeless” touchscreen devices without bezels or designs in which the touch interface wraps around the sides of the device. The widespread adoption of this technology is dependent on making metal lines finer to make them invisible and eliminate moiré patterns when coupled with displays.
Silver nanowires are another exciting and promising prospect. A percolated network of single crystal silver nanowires results in highly conductive layers with excellent transparency and unmatched flexibility. Transparent conductive films based on silver nanowires promise to enable widespread use of touch by achieving much lower cost than ITO sensors.
First, silver is 50 to 100 times more conductive than ITO, resulting in much lower material costs. Second, unlike ITO, silver nanowires are deposited from water-based inks in a high-throughput roll-to-roll process, enabling low-cost film production. In addition, the low processing temperatures enable very high conductivity even on flexible plastic substrates.
Unlike graphene, silver nanowires are commercially available on thin, flexible plastic substrates from multiple suppliers. These silver nanowire films fit into current production lines designed for ITO sensor manufacturing and. In fact, they’re already being used in several touchscreen devices on the market.
For example, thin, light, and shatter-proof large area touchscreens for ultrabooks, all-in-one computers, and monitors enabled by low-resistance silver nanowire films are scheduled to be on the market later this year. This material presents immense opportunities for developers exploring new designs, including flexible displays and curved surfaces.
With the emergence of new, superior transparent conductive materials, the projected capacitive touch device market is on the verge of a metamorphosis. ITO will be replaced by lighter, bendable films that deliver enhanced optical quality at lower production cost.
Smart phones, tablets, ultrabooks, and other existing devices will be thinner, lighter, and more responsive. Moreover, better, cheaper transparent conductive materials will drive technological experimentation and progress, opening the door for cutting-edge designs and enabling a bright future for touchscreens.