1. Digital Micromirror Devices (DMD)
ECE 5320 – Mechatronics
Utah State University
Brett Rogers

2. Outline Major applications Basic Working Principle Illustrated
A Typical Sample Configuration in Application
Specifications
Limitations
History
Links and Other Resources
Reference list

3. Major Applications Digital Light Processing (DLP) projectors[5]
Volumetric Displays[7]
Print Setting[7]
Printed Circuit Board (PCB) Manufacturing[7]
Semiconductor Patterning[7]
Holographic Data Storage[7]

4. Functional Overview Array of tiny mirrors (up to 2 million)
Each mirror is 16µm x 16µm
Each mirror pivots about a fixed axis1
Each mirror acts as a digital light switch
ON: Light is reflected to desired target
OFF: Light is deflected away from target
Pulse Width Modulation (PWM) techniques are used to perform digital light modulation
MEMS: fabrication process similar to CMOS

5. Conventional DMD Construction
Source: Jeffery B. Sampsell; “An Overview of the Performance Envelope of Digital Micromirror Device (DMD) Based Project Display Systems”; Texas Instruments
Source: Larry J. Hornbeck; “Current Status of the Digital Micromirror Device (DMD) for Project Television Systems;” Texas Instruments

6. Mirror Mounting Mechanism
Each mirror is mounted on Hinge Support Posts
Each mirror rotates about the posts
Torsion hinge restores the mirror to its default horizontal state when no power is applied to the circuit
Source: Larry J. Hornbeck; “Current Status of the Digital Micromirror Device (DMD) for Project Television Systems”; Texas Instruments

7. Mirror Rotation
Each mirror rotates +/- 10° for total rotational angle of 20°
Landing Electrode provides stop pad for the mirror and allows precise rotational angles
Source: Larry J. Hornbeck; “Current Status of the Digital Micromirror Device (DMD) for Project Television Systems”; Texas Instruments

8. Bias Bus & Address Electrodes
Bias/Reset Bus provides stop pad and connects all mirrors to allow for a bias/reset voltage waveform to be applied to the mirrors
Address electrodes are connected to an underlying SRAM cell’s complimentary outputs
Source: Larry J. Hornbeck; “Current Status of the Digital Micromirror Device (DMD) for Project Television Systems”; Texas Instruments

9. SRAM Cell
Complimentary SRAM cell outputs connected to the address electrodes actuate the mirrors by electrostatically attracting/repelling the free corners of the voltage-biased mirrors
Source: Larry J. Hornbeck; “Current Status of the Digital Micromirror Device (DMD) for Project Television Systems”; Texas Instruments

10. Modern DMD Construction
Source: Larry J. Hornbeck; “Current Status of the Digital Micromirror Device (DMD) for Project Television Systems”; Texas Instruments
Source: Gary A. Feather; “The Digital Micromirror Device for Project Display”; Texas Instruments

11. 3-D Model
Source: Begon Martin, Ciapala Richard, Deaki Zoltan; “Reliability of MEMS: Case Study”; Ecole Polytechnique Federale De Lausanne

12. DMD As An Actuator/Sensor
DMDs have these actuating components
Rotation caused by torsion spring
Rotation caused by electromagnetic forces
DMDs have these sensing components:
Bias/Reset bus electrode
Address bus electrode
Electromagnetic properties of the mirror
SRAM cell

13. Application of DMD in DLP
DMD is the technology of Digital Light Processing (DLP) projectors
DMD reflects incident light toward or away from optical lens
Optical lens projects image on screen
Each mirror of DMD corresponds to one pixel of projected image

14. Three-Pixel DLP Projector Example
Source: Lars A. Yoder; “An Introduction to the Digital Light Processing (DLP) Technology”; Texas Instruments

15. Full DLP System Pictorial Overview
Source: Larry J. Hornbeck; Digital Light Processing: A New MEMS-Based Display Technology; Texas Instruments

16. DLP Integrated Circuit
Source:

17. DMD Specifications Mirror Size = 16µm x 16µm (17µm centers) [3]
Resonant Frequency = 50kHz [3]
Switching Time < 10µSec [4]
Total Rotational Angle = 20°[3]
Total Efficiency of Light Use > 60%[6]
Fill Factor per Mirror = 90%[6]

18. Potential Energy of Mirror
Potential Energy of Mirror as a Function of Angle and Voltage Bias (address voltage = 0)
Source: Larry J. Hornbeck; “Digital Light Processing: A New MEMS-Based Display Technology”; Texas Instruments

19. Switching Response
Three variables are plotted as a function of time: the bias/reset voltage, the cross-over transition from +10 degrees to -10 degrees, and the same-side transition for a mirror that is to remain at +10 degrees. Shortly before the reset pulse is applied, all the SRAM memory cells in the DMD array are updated. The mirrors have not responded to the new memory states because the bias voltage keeps them electromechanically attached.[5]
Source: Larry J. Hornbeck; “Digital Light Processing: A New MEMS-Based Display Technology”; Texas Instruments

20. DMD Limitations: Hinge Memory[8]
Hinge memory is largest failure of DMD
Occurs when mirror remain in one position for extended period of time
Torsion hinge no longer restores mirror to perfectly horizontal position
Bias voltage must increase to compensate

21. Bias Voltage Compensation
Source: Begon Martin, Ciapala Richard, Deaki Zoltan; “Reliability of MEMS: Case Study”; Ecole Polytechnique Federale De Lausanne

22. Mirror Affected by Hinge Memory
Front mirrors are perfectly horizontal, while rear mirrors maintain a residual tile due to hinge memory.
Source: Begon Martin, Ciapala Richard, Deaki Zoltan; “Reliability of MEMS: Case Study”; Ecole Polytechnique Federale De Lausanne

23. Hinge Memory Lifetime
Source: Michael R. Douglas; “DMD reliability: a MEMS success story”; Texas Instruments

24. History Developed by Texas Instruments (TI) [2]
DOD initially funded TI to develop a light modulator [2]
Project Team Leader: Dr. Larry Hornbeck [2]

25. History: From Analog to Digital I[2]
Deformable Mirror Device [2]
Analog Version of Digital Micromirror Device
Work began in 1977
Analog voltage across air gap deformed mirror to produce different light intensities
Idea was scrapped in 1986

26. History: From Analog to Digital II[2]
Digital Micromirror Device [2]
Digital approach to light modulation
Use pulse width modulation (PWM) principles to turn the mirror “on” and “off”
First DMD was built and tested in 1987
Unlike the Deformable Mirror Device, DMD does not change light intensity. But human eye integrates the Pulse Width Modulated signal to form different shades of color

27. Web Links and Other Information
Texas Instrument’s Official DLP Site:
Flash Demo of DLP:

28. Quote
“If you’re afraid to fail, then your actions may not be as bold, aggressive or creative as you need them to be in order to accomplish your goal. You may play it so conservative you never get there.”2 - Dr. Larry Hornbeck

29. References
What is DLP?,;
“The Digital Micromirror Device, A Historical Landmark”; Texas Instruments and The American Society of Mechanical Engineers (ASME); 1996;
Gary A. Feather, David W. Monk; “The Digital Micromirror Device for Project Display”; 1995 International Conference on Wafer Scale Integration
Larry J. Hornbeck; “Current Status of Digital Micromirror Device (DMD) for Projection Television Applications”, 1993
Larry J. Hornbeck; “Digital Light Processing: A New MEMS-Based Display Technology”; Texas Instruments
Lars A. Yoder; “An Introduction to the Digital Light Processing (DLP) Technology”; Texas Instruments
Dana Dudley, Walter Duncan, John Slaughter; “Emerging Digital Micromirror Device (DMD) Applications”; Texas Instruments
Begon Martin, Ciapala Richard, Deaki Zoltan; “Reliability of MEMS: Case Study”; Ecole Polytechnique Federale De Lausanne
Michael R. Douglas; “DMD reliability: a MEMS success story”; Texas Instruments