NTera's technology adds another twist: The metal oxide display material is transparent when not charged, laying a foundation for transparent displays. "An overlay on top of a window could be realized," similar to what moviegoers saw in Minority Report, says Briancon. But NTera's current products are still built on glass.
Kent Displays, is developing a bistable LCD based on cholesteric technology. The supertwisted nematic LCDs used today twist constituent liquid-crystal molecules about 270 degrees, says sales and marketing manager Tony Emanuele. Kent's technology twists the molecules 16 or 17 times. When twisted that tightly, the molecules don't readily unwind, making the display bistable.
In the lab, Kent has demonstrated its technology deployed on plastic, paper and even fabric substrates. "The chemical recipe for cholesteric lends itself more readily to plastic substrates," Emanuele says, because it has 1/1,000th the barrier requirement of standard LCDs. Kent's current displays use a relatively slow passive matrix and are best suited for applications such as e-books and signage. The technology includes two-color combinations of either yellow/black or blue/white. Early units are fairly small, at 2.5 by 1.5 in., and offer 100-dpi resolution. Kent is working on a faster, active-matrix display and expects to be able to manufacture its passive-matrix version on flexible substrates by year's end. "Two to three years from now, flexible displays on plastic will be commonplace," Emanuele predicts.
In addition to the technical challenges, flexible displays face several other hurdles before they can become commercially viable. "Making [displays] on glass is hard enough," says iSuppli's Allen. Jet printing requires an entirely different, if potentially cheaper, manufacturing process that is still in the early stages of development. Until volume production is possible, jet-printed displays will be expensive relative to alternative technologies. For example, in the e-paper market, simple paper shelf labels and signage can't be updated electronically, but they're far cheaper, Allen says.
The key, says Jeremy Burroughes, CTO at Cambridge Display Technology, is to find a profitable niche for early designs. "The hurdle is always to find early areas to get into first," he says, "and gradually build up the knowledge and revenue profile to go into more advanced areas."
The economies of printed electronics
Jet printing enables flexible displays, but what will drive manufacturers toward ink-jet- and polymer-based substrates are the potential manufacturing cost savings, says Jim Brug, imaging materials department manager at HP Laboratories. "One of the big things going on in material science is moving beyond the inorganic thin-film technologies [such as amorphous silicon] to solution-based materials where you can actually spray these things out of an ink jet," he says. Unlike inorganic substances like amorphous silicon, organic semiconductor materials can be applied in liquid form.
HP Labs has developed an ink-jet printing and lamination process that could replace the vacuum deposition and photolithography techniques used to make today's active-matrix LCDs.
Printing on thin polymer sheets allows for a more efficient, automated process than the discrete manufacturing techniques used to produce individual silicon chips on a production line. Electronics can be printed on continuous polymer sheets, a process called roll-to-roll printing. "These are primarily issues of cost," says Bob Street, senior research fellow at Palo Alto Research Center. "The idea is one can use printing presses rather than silicon fabs to make these devices."
"Printing a display using roll-to-roll processing will allow it to be a very low cost, even disposable type display," says Brug. HP Labs is researching two processes: ink jetting and imprint lithography, where fine circuit patterns are pressed onto a plastic substrate.Xerox Corp.is working on processes for both polymers and stainless-steel foil substrates.
"This world of digital fabrication will open up very low-cost manufacturing plants that don't cost an arm and a leg to build. Does that mean you don't need cleanrooms? That's right," says Brug.
While the potential manufacturing economies are large, don't expect to run down to your local Staples to purchase organic ink cartridges and polymer sheets for printing electronics on your ink-jet printer. "We're not going to be making displays on our desks anytime soon," Brug says.
From flexible displays to bendable PCs
If ink-jet printing technologies can be used to lay down transistors for flexible displays today, what's to prevent other electronics -- perhaps an entire computing device -- from being embedded in that same polymer sheet? Jim Brug at HP Labs thinks the development of flexible computing devices is just a matter of time, as laptops and wireless PDA phones converge. "Will there be a world where your wristwatch will be your PC? One can imagine it coming out," he says. It's also possible that as more electronics are printed on polymer, they could be absorbed into the phone display, allowing contoured or even flexible, wearable designs.
Vendors are already working on embedding display driver circuitry onto polymer substrates, something that's done with today's glass-based displays. In addition, battery vendors such as Solicore, have developed flexible batteries that can be embedded into items such as radio frequency identification (RFID) tags and displays for smart cards. "We're taking the materials that are used for flexible electronics and embedding those into our battery," says Michael Mahan, vice president of business development at Solicore. Such devices, however, aren't strong enough to power a cell phone.
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