Electronic Design

Flexible Displays: A Tantalizing Technology In Search Of A Killer Application

Imagine what you could do with a bendable, rollable, or floppy display panel. You could read your morning newspaper on your PDA and then roll it up when you’re finished. Or you can use your mobile phone to do the same thing. Some market research analysts foresee growing market opportunities for flexible displays, but only if certain issues can be solved.

According to iSuppli Corp., the market will grow by 83.5 percent per year, going from $5 million this year to $339 million by 2013 (Fig. 1). The market research firm expects the largest application for flexible displays to be in cards for financial payments, membership in stores, and gift certificates. These cards would display cardholder information like account balances and transactions. The next biggest application would include electronic shelf labels and point-of-purchase displays.

So where does the industry stand? Many prototypes have been developed and demonstrated. Yet they still remain laboratory curiosities, leaving flexible display manufacturers looking for a “killer” application. Judging from the U.S. Display Consortium’s (USDC) Flexible Display and Microelectronics Conference in March, gains are being made in materials and process issues, but more needs to be done. While progress on issues like barrier coatings and substrate materials has been made, other issues like interconnects, better yields as displays get larger, and the need for an improved supply chain of materials still remain challenging.

Examples of progress include Dow Corning’s announcement that it is moving closer to developing silicon-carbide (SiC) alloy barrier films on flexible substrates for low-moisture permeability applications. Vitex Systems said it was tooling up a manufacturing line to develop high-barrier plastic-film substrates produced in a rolled format for flexibility. And, Sigma Technologies International has reported on a technique to produce flexible organic and inorganic electroluminescent devices.

Last September, Philips’ subsidiary Polymer Vision NV showed off a 5-in. diagonal rollup display at a European consumer electronics show that demonstrates the technology’s viability. The company expects it to be ready for the market by next year. The e-reader Radius product is based on a display module that’s 100 µm thick and features QVGA resolution of 320 by 240 pixels. When it’s not in use, it can be rolled up with a radius of less than 7.5 mm. Rolled up, it measures just 100 by 60 by 20 mm. With four gray levels, the monochromatic display features a 10:1 contrast ratio.

The Polymer Vision Radius uses a bi-stable electrophoretic proprietary material made by E-Ink Corp., holder of many patents on flexible display inks. The material consists of millions of tiny microcapsules, each about the diameter of a human hair. In one incarnation, each microcapsule contains positively charged white particles and negatively charged black particles suspended in a clear fluid. When a negative electric field is applied, the white particles move to the top of the microcapsule, where they become visible to the user. This makes the surface appear white at that spot. At the same time, an opposite electric field pulls the black particles to the bottom of the microcapsule, where they are hidden. By reversing this process, the black particles appear at the top of the microcapsule, which makes the surface appear dark at that spot (Fig. 2).

Early this year, British Plastic Logic announced the development of the world’s largest plastic display, one with a 10-in. diagonal (Fig. 3). The display has a resolution of 100 pixels/in. and four gray levels. Many members of the flexible display industry say it represents the state of the art. It could be ready as a commercial product in three years, according to Plastic Logic, when it would be attached to small electronic devices such as mobile phones and then rolled up and tucked away when it’s not in use.

One firm very active in developing flexible displays is Universal Display Corp. (UDC). The company is in the forefront of developing flexible organic LEDs (FOLEDs) and has R&D contracts with industry giants like Samsung, Tohoku Pioneer, DuPont Displays, Toyota, and Toshiba. UDC recently received a $500,000 extension to a successfully completed Small Business Innovative Research (SBIR) Phase II contract from the U.S. Army’s Communications Electronics Research and Development Engineering Center (CEDEC). The extension builds on UDC’s work in developing full-color active-matrix OLEDs fabricated on flexible metal foils.

As things stand, it may well take a few more years before commercially viable flexible displays will find market applications. There’s no doubt about the technology’s capabilities, though. What remains is developing the right cost-effective applications.

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