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.
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.