Interferometric Modulator Display Information

Interferometric modulator display (IMOD, Mirasol)^[1] is a technology used in electronic displays that can create various colors through the interference of reflected light. The color is selected with an electrically switched light modulator comprising a microscopic cavity that is switched on and off using driver integrated circuits similar to those used to address LCD displays. An IMOD based reflective flat panel display includes hundreds of thousands of individually IMOD elements each a microelectromechanical systems (MEMS) based device.

In one state an IMOD subpixel reflects light at a specific wavelength, while in a second state it absorbs incident light and appears black to the viewer, using a diffraction grating effect.^[2] When not being addressed, an IMOD display consumes very little power. Unlike conventional back-lit LCD displays (and like other reflective display technologies), it is clearly visible in bright ambient light such as sunlight. IMOD prototypes are currently capable of 15 frames per second and are expected to reach 30, suitable for video playback.^[3]

Working principle

A pixel in an IMOD based display consists of one or more subpixels that are actually individual microscopic interferometric cavities similar in operation to Fabry-Pérot interferometers (etalons), and the scales in butterfly wings. While a simple etalon consists of two half-silvered mirrors, an IMOD comprises a reflective membrane which can move in relation to a semitransparent thin film stack.^[4] With an air gap defined within this cavity, the IMOD behaves like an optically resonant structure whose reflected color is determined by the size of the airgap. Application of a voltage to the IMOD creates electrostatic forces which bring the membrane into contact with the thin film stack. When this happens the behavior of the IMOD changes to that of an induced absorber. The consequence is that almost all incident light is absorbed and no colors are reflected. It is this binary operation that is the basis for the IMOD's application in reflective flat panel displays. Since the display utilizes light from ambient sources, the display's brightness increases in high ambient environments (i.e. sunlight). In contrast, a back-lit LCD display suffers from incident light.

For a practical RGB display, a single RGB pixel is built from several subpixels, because the brightness of a monochromatic pixel is not adjusted. A monochromatic array of subpixels represents different brightness levels for each color, and for each pixel, there are three such arrays: red, green and blue.^[5]

Development

The IMOD technology was invented by Mark W. Miles,^[6][2] a MEMS researcher and founder of Etalon, Inc., and (co-founder) of Iridigm Display Corporation.^[6] Qualcomm took over the development of this technology after its acquisition of Iridigm in 2004^[2], and subsequently formed Qualcomm MEMS Technologies (QMT).^[7] Qualcomm has allowed commercialization of the technology under the trademark name "Mirasol",^[8] and this energy-efficient, biomimetic technology sees application and use in e-readers and mobile phones,^[1] etc.

Commercial uses

Future IMOD panels manufacturers include, Qualcomm in conjunction with Foxlink, having established a joint-venture with Sollink (高強光電) in 2009 with a future facility dedicated to manufacturing IMOD panels. The factory production for this began in Jan 2011, with the fabricated panels for devices such as e-readers.

IMOD displays are now available in the commercial marketplace. QMT's displays, using IMOD technology, are found in the Acoustic Research ARWH1 Stereo Bluetooth headset device, the Showcare Monitoring system (Korea), the Hisense C108,^[9] and mp3 applications from Freestyle Audio and Skullcandy. In the mobile phone marketplace, Taiwanese manufacturers Inventec and Cal-Comp have announced phones with Mirasol displays, and LG claims to be developing 'one or more' handsets using Mirasol technology. These products all have only 2-color (black plus one other) "bi-chromic" displays.

Notes

1. ^ ^{a b} "Interferometric Modulator (IMOD) Technology Overview" (PDF). Qualcom. May 2008. http://www.qualcomm.com/common/documents/white_papers/QMT_Technology_Overview_12-07.pdf. Retrieved 2008-08-07.
2. ^ ^{a b c} Product design, nature's way money.cnn.com, June 12 2007: 2:04 PM EDT
3. ^ GeeksHive blog: Qualcomm Mirasol launch its color e-Reader. July 7, 2010.
4. ^ Miles, M.; Larson, E.; Chui, C.; Kothari, M.; Gally, B.; Batey, J. (2003), "Digital Paper for Reflective Displays", SID International Symposium, Boston, Massachusetts, pp. 209–215
5. ^ Waldrop 2007
6. ^ ^{a b} http://www.freepatentsonline.com/5835255.html free patents online.
7. ^ http://query.nytimes.com/gst/fullpage.html?res=9A02EFDD1530F933A2575AC0A9629C8B63 NYTimes.com.
8. ^ "Mirasol". Qualcomm. Feb 2009. http://www.mirasoldisplays.com.
9. ^ Ultra Low-power Handset to Begin Shipping in China in 2008 PRNewswire, BARCELONA, Spain, February 11

References

• M. Mitchell Waldrop (November 2007). "Brilliant Displays" (print). Scientific American (Scientific American, Inc.): pp. 94–97. "(subtitle) A new technology that mimics the way nature gives bright color to butterfly wings can make cell phone displays clearly legible, even in the sun's glare."

• Duncan Graham-Rowe (October 2007). "Epaper Displays Video" (print). Technology Review (Technology Review, Inc.). "(subtitle) A novel electronic-paper display developed by Qualcomm can deliver high-quality video images, making it more versatile than other e-paper technologies."

• "Uni-Pixel TMOS display". http://www.unipixel.com/tech.htm. Retrieved 20 October 2009.

Categories: Display technology | Emerging technology

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