Nanotubes and Nanoparticles
Photo courtesy of Oak Ridge National Laboratory.

It no longer takes much foresight to imagine the mobile world of the future, a world in which smart phones and other handhelds combine voice and data communications, with a considerable amount of computing capabilities. Video will be part of the mix, too. Different handheld devices will have different orientations, of course. There will be PDA-like devices which focus on data, iPOD-like devices that are video capable and advanced cell phones, which for all their additional functionality are in the end just voice machines. But despite these different strengths, the multifunctional handheld devices of the future are going to require much better displays than the small LCD displays that have been typical of handhelds in the past.

There are some good historical reasons to think that the contributions made by advanced materials are the key to the display needs of the handheld sector. It was the advent of good LCD screens that made mobile computing possible. LCD was also the main enabler of large flat-panel displays (FPDs) for television and then the arrival of plasma made those FPDs even better.

It is therefore not surprising that those looking for better displays in the handheld sector have focused on new materials platforms. Solutions that have been offered include MEMS, liquid-crystal-on-silicon, and field emission displays (FEDs). However, these have usually brought new problems in their wake -- high power usage, visual distortions and so on.

Here are some highlights from NanoMarkets' new report, The Market for Flexible Displays and Field Emission Displays: How Plastic Electronics and Carbon Nanotubes are Creating New Opportunities in the Display Business, in which we examine the impact of nanotube electronics and plastic electronics, two technology/materials platforms that we believe are on the verge of producing a new generation of displays that preserve the achievements of the current level of handheld display technology, while solving some of the problems that handheld displays now face.

Plastics, Displays and Printability

Plastic electronics is an emerging technology/materials platform in which circuitry is created with conductive molecules that are somehow layered onto a substrate. In the case of displays, the light is supplied by a layer of organic LEDs (OLEDs). However, there are outstanding materials and technology issues that have yet to be settled and which will ultimately shape this sector:

Vapor Deposition vs. Ink-Jet: In terms of manufacturing, the two options for plastic displays seem to be vapor deposition and ink-jet printing. Vapor deposition is a highly mature process and is, for example, being used by Kodak to create its plastic displays. The alternative is ink-jet printing, using industrial ink-jet printers. Based on our interviews, there still seems to be some controversy about just how mature ink-jet printing really is at the present time. However, there can be little doubt that ink-jet printing is the holy grail of plastic electronics, since it seems to change the economics of manufacturing in electronics from favoring very high production runs in massively expensive fabs to an environment in which modest runs are profitable and circuitry can be easily customized. This will impact not only the display business, but also RFIDs, membrane keyboards, computer memory and photovoltaics.

Manufacturing technology is in a state of flux. Whatever the current merits of ink-jet versus deposition approaches may be, both approaches are improving. Backers of ink-jet technology, point out that once plastic electronics takes off, specialist ink-jets for plastics electronics will appear and help improve yields. At the moment, general-purpose printing machines are being used. One design direction for specialist ink-jet printers aimed at the plastic electronics market would be designs with printheads optimally suited to polymer or metallic inks.

Materials technology is immature too. Universal Display Corp. is touting its display technology that uses small molecules to create phosphorescent OLEDs. It claims good color quality, but is using a vapor deposition process to create displays. Cambridge Display Technology uses polymers and the potentially revolutionary ink-jet process. But it is still working on long-lifetime blue OLEDs. A materials platform that can produce ink-jet printable displays with high color quality and that will also last a few years still seems like a thing of the future.

Plastics, Displays and Flexibility The future evolution of plastic display technology will also occur not just in the materials for OLEDs and the production technology, but in the materials for substrates, as well. Although many people use the term "printable displays" and "flexible displays" as interchangeable terms, they are actually different. OLED displays, even if they are printed, do not necessarily use a flexible substrate. Fujitsu is using a color OLED sub-display in one of its cell phones, but the substrate is glass.

Using a plastic substrate instead of glass reduces and weight and makes displays less likely to break when a mobile device is dropped. These are important reasons for moving to a plastic substrate. But what a plastic substrate also does is enable flexibility in addition to printability. Some firms, such as CDT, E Ink, Philips and Plastic Logic are working towards displays that employ a flexible substrate and hence can be rolled up just like paper. The term "electronic paper" has been coined for this type of product, which is paper-like not only in its flexibility and thinness, but in its ability to be read from many angles. Some R&D work is even being done to make "electronic paper," feel like paper.

Flexible displays that can be rolled up may be no more than a novelty in the general cell phone sector, but for a high-end smartphone with extensive computing capabilities or a miniature video player, the ability to roll-up a medium-sized display and unfurl it for use may have a lot of value. Trying to watch a movie or search a Website on a display that measures just a few square inches could never be a pleasant experience and the roll-up display means that a laptop-sized device no longer is essential if something other than a tiny screen is required. A roll-up display would enable a much larger display to be used than would be possible if a rigid display was being used, and would bring the viewing experience closer to what a consumer would be used to with a television screen.

A Role for CNTs?

NanoMarkets' research also suggests carbon nanotubes (CNTs) may have a role to play in displays for future mobile devices. This may occur either as part of the plastic display programs described above or as an alternative to such programs.

One possibility is to use a CNT composite as an alternative to the sputtered indium tin oxide (ITO) that is used to conduct electricity to cells in either glass or plastic displays. This has been proposed by Eikos, which claims the advantages of using its composite over ITO include improved flexibility, printability and color. Cost can also be reduced, according to Eikos, since vacuum processing is not required and the Eikos approach effectively replaces indium (a scarce commodity) with carbon (an almost ubiquitous element.) DuPont has also worked in this space and has developed a polyaniline/CNT composite that the company says is suitable for printable electronics in display backplanes.

And although plastic/flexible displays seem certain to be the next big thing in mobile displays, it is possible that they may be challenged by CNT-based FEDs by late in this decade. Just a few years back, FEDs were being seriously considered for the mobile sector. However, the FEDs of the time utilized a kind of microtechnology that ultimately floundered on technical problems. FEDs have now been reinvented using carbon nanotubes. They operate on a similar principle to CRTs, but they are lighter, less power consuming and flatter, and they also boast very high-quality video display.

This new generation of CNT-based FEDs is not being aimed at the mobile sector. Instead, they will first appear in the form of large television screens and advertising displays, which are segments of the display market that most manufacturers believe will be willing to swallow their relatively high R&D costs. However, given the high quality of the FED's video output -- which may well surpass what plastic electronics can offer -- coupled with low weight and power consumption, it would be no surprise to see FEDs return to the mobile segment eventually. At least one firm -- cDream -- says that it already has plans to enter that sector and others may follow once FEDs have moved down the cost curve.

Bottom Line

In a recent presentation to a nanotechnology business conference, an executive from Motorola told the audience that the most important problem that had to be solved before ubiquitous computing could become a reality was that better power sources had to be found, since the current generation of lithium-ion batteries were not up to the task. However, according to this source, the second most important problem for most ubiquitous computing was better displays, meaning ones that could more adequately show high-quality video and images as well as serve for note taking, etc.

In a multimedia mobile world, displays will be required to serve multiple purposes and provide effective information output. The emerging generation of displays that are being enabled by the latest developments in material science will go a long way to meeting such requirements.

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Editor's note: This article is from NanoMarkets' new report, The Market for Flexible Displays and Field Emission Displays: How Plastic Electronics and Carbon Nanotubes are Creating New Opportunities in the Display Business. For additional information see the NanoMarkets website at www.nanomarkets.net.