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Full Version: Digital Micro mirror Device (DMD)
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For the past six years, Digital Light Processing technology from Texas Instruments has made significant inroads in the projection display market. With products enabling the world?s smallest data and video projectors, HDTV?s, and digital cinema, DLP technology is extremely powerful and flexible. With success of the DMD as a spatial light modulator for projector applications, dozens of new applications are now being enabled by general- use DMD products that are recently available to developers. The same light switching speed and ?on-off? (contrast) ratio that have resulted in superior projector performance, along with the capability of operation outside the visible spectrum, make the DMD very attractive for many applications, including volumetric display, holographic data storage, lithography, scientific instrumentation, and medical imaging. Texas Instruments DLP display technology digitally manipulates (or processes) light to produce film-like, all-digital images. DLP integrates a projection lamp and an electronic video signal from a source such as a VCR or computer, and the processed light produces an all-digital picture. The key to this complete digital process is the Texas Instruments Digital Micro mirror Device (DMD), a thumbnail-size semiconductor light switch. The DMD consists of an array of thousands of micro-scopic size mirrors, each mounted on a hinge structure so that it can be individually tilted back and forth. When a lamp and a projection lens are positioned in the right places in the system, DLP processes the input video signal and tilts the mirrors to generate a digital image.
Digital Micromirror Device

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Applications

Mainly projection systems (Digital Light Processing)
Other emerging applications such as 3D metrology, confocal microscopy,digital TV

Hinge fatigue

Fatigue: slow growth of a crack driven by repeated plastic deformation
Mirror in normal operating mode switches every 200 microseconds
5 years use with 1000 operating hours a year  mirrors switch 90x109 times
First approach: anaylsis using bulk properties of the hinge material  showed that fatigue would be a big problem
However… accelerated tests proved that wrong, samples easily exceeding 100x109 switches showing no fatigue.
Explanation: hinge so thin  governed by thin film properties!

Hinge memory

Most significant mode of failure
Occurs when a mirror operates in the same direction for a long period of time
Main factors are the duty cycle and the operating temperature
Duty cycle: percentage of time a mirror is addressed to one side.(95/5)
Temperature is the dominant factor for hinge memory lifetime

Stiction

Induced by an excessive adhesive force between the landing tip and its landing site
Adhesive forces can be induced by:
Surface contamination
Capillary condensation
CMOS defects
Van der Walls forces

Reliability testing can be done to measure the distribution of surface adhesion across the device to determine the number of operating devices under different switching voltages

Environment robustness

Based on standard semiconductor tests requirement
Capillarity force
Humidity everywhere
UV light exposure
Thermal testing
Surface contamination
During production process

Size vs Robustness

Small size enable robustness to mechanical shocks
Lowest resonant frequency in KHz
Test :1500G and 20G in vibration with no mirror breaking
Weaknesses on the package identified and annihilated

Summary of DMD reliability

Hinge memory lifetime
>100’000 hours at normal operating conditions
Random defects
>650’000 hours MTBF (<1500 FIT)
Hinge fatigue lifetime
>3.67 trillion cycle or >250’000 hours
Environmentally robust

Conclusion

Misleading apparence
Experience plan must be done to find critical failure modes
Concern to reliability
The reliability of the DMD has been exemplary and should be considered as a reference for development of other MEMS