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E-Reader Display Shows Vibrant Color Video

Mirasol’s reflective display is being tested by device manufacturers, and could appear on shelves next year.
November 15, 2011

Even as the processing power and download speeds of mobile devices surge, one component still lags behind: the screen. LCD panels use significantly more power than any other component of a phone or tablet because of their need to pump out bright light to form an image.

Image innovation: This tablet can play video or games, but has a display that uses microscopic mirrors to make an image from ambient light, enabling longer battery life.

The only practical alternative is e-ink, the technology used in the Amazon Kindle; it consumes orders of magnitude less power but sacrifices color and the ability to change images fast enough for video playback or smooth game play.

Now, after years of waiting, alternative technology that promises the best of both approaches is finally edging closer to commercialization. During a recent visit to mobile chipmaker Qualcomm’s headquarters in San Diego, Technology Review tried out a full-color, 5.7-inch Android tablet with a display that offers rich colors under bright light, close to those of an LCD and not unlike the pages of a magazine. The prototype screen was also responsive enough for video playback and for a game of Angry Birds; it can deliver up to 30 frames per second.

Because the device’s screen uses ambient light, like a printed page or e-ink display, the power consumption is a tenth or less of that of a comparable LCD, although the display also features a built-in light for use in the dark. Known as Mirasol, the technology was created by a startup company, Iridigm, acquired by Qualcomm in 2004.

“In the market today, you have the iPad at one end and things like e-ink at the other end. This is really meant to bridge both of those worlds,” says Clarence Chui, who leads the group at Qualcomm developing the new technology. “It is extremely low power, full color, and can be looked at wherever you go.”

The Mirasol display makes color in the same way as the wings of iridescent butterflies or peacock feathers—by being an imperfect mirror that tunes the color of incoming light before reflecting it back to the viewer.

In a Mirasol display, this is done by small cavities known as interferometric modulators, tens of microns across and a few hundred nanometers deep, beneath the display’s glass surface. “It’s the air gap between the back of that glass and a mirror membrane at the bottom of the modulator that sets the color,” says Chui. Each modulator’s mirror membrane can snap upward against the glass when a small voltage is applied, closing the cavity and displaying a black color to the viewer. Mirasol modulators are made using techniques similar to those used to pattern metals and deposit materials in computer chip manufacturing.

Modulators come in three types: for red, green, and blue. Each pixel in a Mirasol display is actually made up of several modulators that display the three basic colors at different brightness levels. Switching these modulators on and off in the right combination offers full color at different brightness. In dark conditions, light is directed onto the panel’s modulators from LED lights at the edge of the panel.

A study by Pike Research published last year estimated that a 5.7-inch Mirasol display like the one seen by Technology Review would allow for at least twice as much Web browsing as an equivalent device with an LCD screen. Qualcomm plans to sell the displays to the same device makers—including HTC, LG, and Samsung—that already buy its mobile chips.

Chui says displays will be made to serve both full-size tablets and phones and that demonstration tablets and display components have already been provided to various partners.

However, Qualcomm is far behind its own previous public predictions of when the technology would appear in products. Technology Review and others were shown an e-reader last year, and were told that devices would be on shelves in 2011. Chui said that the Mirasol technology needed significant modifications before it would make economic sense to manufacture it.

The device seen by Technology Review was made in a pilot factory in Taiwan that has mostly produced sample displays distributed to potential partners and customers, although a relatively small number of commerical displays will be made there. Chui says that a second, larger factory in Taiwan, big enough for production at a very large scale, is under construction and will come online in mid-2012. With the larger factory incomplete, truly mass-market devices with Mirasol displays can only appear in the second half of next year. Qualcomm is planning to invest up to $975 million in the new factory.

Jennifer Colegrove, who follows new display technologies for the analyst company DisplaySearch, says that despite the delays to mass production, the Mirasol technology lacks much serious competition. “It’s really a very unique kind of display,” she says, citing its ability to match LCD for experience at much less power.

One possible rival is an electrowetting display technology being developed by Samsung. It uses voltage to move colored liquids. However, demonstration displays of the technology have so far been less polished than those shown by Qualcomm, says Colegrove.

Colegrove guesses that Mirasol’s debut in products has been hampered by the challenge of ensuring a near-perfect “yield” of the modulators that make up a display. Because millions are required to make each display, even a very low error rate would be problematic. “The LCD industry went through this same problem with yield, and it took years to solve,” says Colegrove. 

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