Digital Micromirror Devices (DMD)

1
Digital Micromirror Devices (DMD)

• ECE 5320 Mechatronics
• Utah State University
• Brett Rogers
• brett.rogers_at_aggiemail.usu.edu

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) projectors5
• Volumetric Displays7
• Print Setting7
• Printed Circuit Board (PCB) Manufacturing7
• Semiconductor Patterning7
• Holographic Data Storage7

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 cells 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

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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

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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 http//www.asme.org/Communities/History/La
ndmarks/53_Digital_Micromirror_Device.cfm
17
DMD Specifications

• Mirror Size 16µm x 16µm (17µm centers) 3
• Resonant Frequency 50kHz 3
• Switching Time lt 10µSec 4
• Total Rotational Angle 203
• Total Efficiency of Light Use gt 606
• Fill Factor per Mirror 906

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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 Memory8

• 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

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History From Analog to Digital I2

• 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

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History From Analog to Digital II2

• 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

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Web Links and Other Information

• Texas Instruments Official DLP Site
  http//www.dlp.com/
• Flash Demo of DLP http//www.dlp.com/includes/dem
  o_flash.aspx
• http//en.wikipedia.org/wiki/Digital_micromirror_d
  evice
• http//www.audioholics.com/education/display-forma
  ts-technology/display-technologies-guide-lcd-plasm
  a-dlp-lcos-d-ila-crt/display-technologies-guide-lc
  d-plasma-dlp-lcos-d-ila-crt-page-2

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Quote

• If youre 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

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References

• What is DLP?, http//focus.ti.com/dlpdmd/docs/dlp
  learningdetail.tsp?sectionId62tabId2249
• The Digital Micromirror Device, A Historical
  Landmark Texas Instruments and The American
  Society of Mechanical Engineers (ASME) 1996
  http//www.asme.org/Communities/History/Landmarks/
  53_Digital_Micromirror_Device.cfm
• 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