The basic elements of an IMOD-based display are microscopic devices that act essentially as mirrors that can be switched on or off individually. Each of these elements reflects only one exact wavelength of light, such as a specific hue of red, green or blue, when turned on, and absorbs light when off. Elements are organised into a rectangular array in order to produce a display screen. An array of elements that all reflect the same color when turned on produces a monochromatic display, for example black and red. As each element reflects only a certain amount of light, grouping several elements of the same color together as subpixels allows different brightness levels for a pixel based on how many elements are reflective at a particular time. Multiple color displays are created by using subpixels, each designed to reflect a specific different color. Multiple elements of each color are generally used to both give more combinations of displayable color and to balance the overall brightness of the pixel. Because elements only use power in order to switch between on and off states, IMOD-based displays potentially use much less power than displays that generate light and/or need constant power to keep pixels in a particular state. Being a reflective display, they require an external light source to be readable, just like paper or other electronic paper technologies.
Details
A pixel in an IMOD-based display consists of one or more subpixels that are individual microscopic interferometric cavities similar in operation to Fabry–Pérot interferometers, 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 semi-transparent thin film stack. 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. In contrast, a back-lit LCD suffers from incident light. For a practical RGB color model 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.
Development
The IMOD technology was invented by Mark W. Miles, a MEMS researcher and founder of Etalon, Inc., and of Iridigm Display Corporation. Qualcomm took over the development of this technology after its acquisition of Iridigm in 2004, and subsequently formed Qualcomm MEMS Technologies. Qualcomm has allowed commercialization of the technology under the trademark name "mirasol". This energy-efficient, biomimetic technology sees application and use in portable electronics such as e-book readers and mobile phones. It has some commercial use Future IMOD panels manufacturers include, Qualcomm in conjunction with Foxlink, having established a joint-venture with Sollink in 2009 with a future facility dedicated to manufacturing IMOD panels. Production for this began in Jan 2011, with the fabricated panels intended for devices such as e-readers. The IMOD Mirasol display laboratory in Longtan, Taiwan, formerly run by Qualcomm, is now apparently run by Apple.
Uses
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, the Hisense C108, 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 two-color "bi-chromic" displays. A multi-color IMOD display is used in the Qualcomm Toq smartwatch.
