Taipei, Taiwan -- Motorola Inc. is known for slim phones, but its latest product announcement takes the unusual step of tapping a new display technology to meet its design goals. The 9-mm-thick Motofone, which targets emerging markets like India and Brazil, uses an electrophoretic display, or EPD--an ultrathin, low-power display often referred to as electronic paper.
This is the first time that an EPD has been used in a mobile phone. The design-in will be a boost for the technology, assuming the Motofone ships in high volume when it is released toward the end of this year.
The use of an EPD in the Motofone caught some analysts and industry players by surprise. They suspect that it will be a loss leader for E Ink Corp. (Cambridge, Mass.)--which is supplying the technology--because of the typically low yield rates of EPDs. The upside, however, is that higher volumes will help engineers tinker with ways to improve yields.
To date, most EPDs have been experimental. Over the long term, companies like E Ink, SiPix Imaging Inc. and a handful of others hope to see these displays more commonly used in applications with flexibility or low-power requirements, such as electronic shelf labels, watches and smart cards. Sony uses an EPD in its Librié e-book, and Lexar uses one as a capacity indicator on a Universal Serial Bus flash drive.
Motorola chose the display for its high contrast, thin profile and power-saving characteristics. Although the Motofone is limited to black and white, that isn't much of a downside in the low-end emerging-markets segment, where a fair amount of monochrome displays are already in use. And its high contrast ratio is very suitable for its target users.
"It will be perfectly viewable in very strong artificial [light] or strong sunlight, which you don't get in an LCD," said David Taylor, who oversees high-growth markets for Motorola. "Most of the emerging markets tend to be in hot countries, where there is a lot of sun, so this is very important."
EPD substrates are made up of tiny pockets containing charged particles suspended in an opaque liquid. When a charge is applied to an electrode, the particles are driven to the top of the pocket, displacing the liquid and appearing at the display's surface. When an opposite charge is applied to a second electrode, the particles are driven to the bottom of the pocket, away from the screen's surface. When the charge is removed, the particles will remain in the same position--hence their low-power advantage.
Electrophoretic displays have been around since the late 1960s. They are highly reflective, so they don't require a backlight--a major source of power drain in a mobile system. Displays already account for about one-third of a typical mobile phone's power budget, and are creeping higher as phones morph into mini-TVs and data terminals that require the screen to be on more often.
If EPD technology could be made to work in a wider variety of mobile systems, battery life would improve.
Although the Motorola design-in is a boost for EPD backers, no one expects to see EPDs displace other emerging displays anytime soon. It's still probable that manufacturers will turn to organic light-emitting diodes (OLEDs) for high-end cell phones, whereas EPDs or other bistable displays will be in the low end.
"EPD technology is not appropriate for cell phones in any other market," said Kimberly Allen, director of display technology at iSuppli Corp. "The switching speed is quite slow--hundreds of milliseconds--which means no video and perhaps noticeable screen-refresh delays. It wouldn't fly in Japan, for instance, so this [Motorola phone] is a very interesting experiment."
Video typically needs a refresh rate of about 15 ms. Active-matrix thin-film-transistor LCDs can deliver 10 to 50 ms, and OLEDs are even speedier at about 100 microseconds. EPDs typically hover between 200 and 500 ms, Allen said, and future generations might achieve 100-ms refresh rates.
Full color also remains a huge limiter. Companies are experimenting with color-filter stacking and multiple colored particles. For instance, E Ink is working with Toppan Printing Co. Ltd. to create color filters that would overlay the displays, but analysts still see the inherent two-color scheme of EPDs as a tough nut to crack, thus limiting usage.
Others are more optimistic, and think the Motorola launch will provide needed momentum for speeding up research. W.M. Lo, business operations director at Solomon Systech Ltd., the Hong Kong company supplying EPD drivers for the Motofone, believes the technology is finally moving into a phase of higher growth.
"Today you see monochrome, with a response relatively slower than LCDs," he said. "But I see the technology moving very fast--going from passive to active, and then from monochrome to color, so that more and more sophisticated applications will be able to use it."
Other concerns for system designers include the long-term reliability of EPDs. So far, they are suitable for consumer or retail applications with a two- to three-year life span, but use in automotive applications would be a gamble, Lo said.
Also, EPDs have a way to go before they can match the manufacturability of OLEDs and, especially, LCDs, said Manoj Thanigasalam, business unit manager for display systems at Dialog Semiconductor Plc., which designs EPD drivers. Still, he saw the use of an EPD in a cell phone as a huge step forward in being able to optimize yield for EPDs, helping to make them more viable.
Indeed, "Once Moto proves it, others will certainly jump in," said analyst Jon Peddie. He expects other vendors will closely watch to see whether making EPDs in quantity will be economical.
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