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The digital micromirror device, or DMD, is the microoptoelectromechanical system (MOEMS) that is the core of the trademarked DLP projection technology from
Texas Instruments Texas Instruments Incorporated (TI) is an American technology company headquartered in Dallas, Texas, that designs and manufactures semiconductors and various integrated circuits, which it sells to electronics designers and manufacturers globa ...
(TI). Texas Instrument's DMD was created by solid-state physicist and TI Fellow Emeritus Dr. Larry Hornbeck in 1987. However, the technology goes back to 1973 with Harvey C. Nathanson's (inventor of MEMS c. 1965) use of millions of microscopically small moving mirrors to create a video display of the type now found in digital projectors.


History

The DMD project began as the deformable mirror device in 1977 using micromechanical analog light modulators. The first analog DMD product was the TI DMD2000 airline ticket printer that used a DMD instead of a laser scanner.


Construction and use

A DMD chip has on its surface several hundred thousand microscopic mirrors arranged in a rectangular
array An array is a systematic arrangement of similar objects, usually in rows and columns. Things called an array include: {{TOC right Music * In twelve-tone and serial composition, the presentation of simultaneous twelve-tone sets such that the ...
which correspond to the pixels in the image to be displayed. The mirrors can be individually rotated ±10-12°, to an on or off state. In the on state, light from the projector bulb is reflected into the lens making the pixel appear bright on the screen. In the off state, the light is directed elsewhere (usually onto a
heatsink A heat sink (also commonly spelled heatsink) is a passive heat exchanger that transfers the heat generated by an electronic or a mechanical device to a fluid medium, often air or a liquid coolant, where it is dissipated away from the device, ...
), making the pixel appear dark. To produce
greyscale In digital photography, computer-generated imagery, and colorimetry, a grayscale image is one in which the value of each pixel is a single sample representing only an ''amount'' of light; that is, it carries only intensity information. Gr ...
s, the mirror is toggled on and off very quickly, and the ratio of on time to off time determines the shade produced (binary
pulse-width modulation Pulse-width modulation (PWM), or pulse-duration modulation (PDM), is a method of reducing the average power delivered by an electrical signal, by effectively chopping it up into discrete parts. The average value of voltage (and current) fed ...
). Contemporary DMD chips can produce up to 1024 shades of gray (10 bits). See
Digital Light Processing Digital Light Processing (DLP) is a set of chipsets based on optical micro-electro-mechanical technology that uses a digital micromirror device. It was originally developed in 1987 by Larry Hornbeck of Texas Instruments. While the DLP imagin ...
for discussion of how color images are produced in DMD-based systems. The mirrors themselves are made of aluminum and are around 16 micrometers across. Each mirror is mounted on a yoke which in turn is connected to two support posts by compliant torsion hinges. In this type of hinge, the axle is fixed at both ends and twists in the middle. Because of the small scale, hinge
fatigue Fatigue describes a state of tiredness that does not resolve with rest or sleep. In general usage, fatigue is synonymous with extreme tiredness or exhaustion that normally follows prolonged physical or mental activity. When it does not resolve ...
is not a problem, and tests have shown that even 1 
trillion ''Trillion'' is a number with two distinct definitions: *1,000,000,000,000, i.e. one million million, or (ten to the twelfth power), as defined on the short scale. This is now the meaning in both American and British English. * 1,000,000,000,00 ...
(1012) operations do not cause noticeable damage. Tests have also shown that the hinges cannot be damaged by normal shock and vibration, since it is absorbed by the DMD superstructure. Two pairs of electrodes control the position of the mirror by electrostatic attraction. Each pair has one electrode on each side of the hinge, with one of the pairs positioned to act on the yoke and the other acting directly on the mirror. The majority of the time, equal bias charges are applied to both sides simultaneously. Instead of flipping to a central position as one might expect, this actually holds the mirror in its current position. This is because the attraction force on the side the mirror is already tilted towards is greater since that side is closer to the electrodes. To move the mirrors, the required state is first loaded into an SRAM cell located beneath each pixel, which is also connected to the electrodes. Once all the SRAM cells have been loaded, the bias voltage is removed, allowing the charges from the SRAM cell to prevail, moving the mirror. When the bias is restored, the mirror is once again held in position, and the next required movement can be loaded into the memory cell. The bias system is used because it reduces the voltage levels required to address the pixels such that they can be driven directly from the SRAM cell, and also because the bias voltage can be removed at the same time for the whole chip, so every mirror moves at the same instant. The advantages of the latter are more accurate timing and a more cinematic moving image. The described failure mode on these is caused by internal contamination usually due to seal failure corroding the mirror supports. A related failure was the glue used between 2007 and 2013, under which heat and light degrades and outgasses: this normally causes fogging inside the glass and eventually white/black pixels. This cannot usually be repaired, but defective DMD chips can sometimes be used for less critical projects not needing rapidly changing patterns if the existing bad pixels can be made part of the projected image or otherwise mapped out, including 3D scanning.


Applications

* Televisions and
HDTV High-definition television (HD or HDTV) describes a television system which provides a substantially higher image resolution than the previous generation of technologies. The term has been used since 1936; in more recent times, it refers to the g ...
s *
Holographic Versatile Disc The Holographic Versatile Disc (HVD) is an optical disc technology that was expected to store up to several terabytes of data on an optical disc 10 cm or 12 cm in diameter. Its development commenced in April 2004, but it never arrived ...
s *
Head-mounted display A head-mounted display (HMD) is a display device, worn on the head or as part of a helmet (see Helmet-mounted display for aviation applications), that has a small display optic in front of one ( monocular HMD) or each eye ( binocular HMD). An ...
s *
Digital cinema Digital cinema refers to adoption of digital technology within the film industry to distribute or project motion pictures as opposed to the historical use of reels of motion picture film, such as 35 mm film. Whereas film reels have to be sh ...
* DLP projectors * Optical Metrology * Laser Beam Machining * Phase space measurement with forward modelingLiu et al., 201
"3D imaging in volumetric scattering media using phase-space measurements"
/ref> * Spatial Light Modulation *
Multivariate optical computing Multivariate optical computing, also known as molecular factor computing, is an approach to the development of compressed sensing spectroscopic instruments, particularly for industrial applications such as process analytical support. "Convention ...
* Digital Holographic Tomography *
Optogenetics Optogenetics is a biological technique to control the activity of neurons or other cell types with light. This is achieved by expression of light-sensitive ion channels, pumps or enzymes specifically in the target cells. On the level of individ ...
{{cite web, url=https://www.mightexbio.com/products/patterned-illumination/polygon/#text-block-15, title=State-of-the-Art Illumination Technology, website=Polygon Cellular-Resolution Optogenetics & Photostimulation, publisher=Mightex Systems, access-date=2021-05-28 *
Flip-disc display The flip-disc display (or flip-dot display) is an electromechanical dot matrix display technology used for large outdoor signs, normally those that will be exposed to direct sunlight. Flip-disc technology has been used for destination signs in ...


References


External links


DLP White Paper Library


American inventions Transducers Semiconductor devices Optoelectronics Microtechnology