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Digital Micromirror Devices (DMD)
ECE 5320 – MechatronicsUtah State University
Brett [email protected]
Outline
• Major applications• Basic Working Principle Illustrated• A Typical Sample Configuration in
Application• Specifications• Limitations• History• Links and Other Resources• Reference list
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]
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
Conventional DMD Construction
Source: Larry J. Hornbeck; “Current Status of the Digital Micromirror Device (DMD) for Project Television Systems;” Texas Instruments
Source: Jeffery B. Sampsell; “An Overview of the Performance Envelope of Digital Micromirror Device (DMD) Based Project Display Systems”;
Texas Instruments
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
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
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
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
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
3-D Model
Source: Begon Martin, Ciapala Richard, Deaki Zoltan; “Reliability of MEMS: Case Study”; Ecole Polytechnique Federale De Lausanne
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
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
Three-Pixel DLP Projector Example
Source: Lars A. Yoder; “An Introduction to the Digital Light Processing (DLP) Technology”; Texas Instruments
Full DLP System Pictorial Overview
Source: Larry J. Hornbeck; Digital Light Processing: A New MEMS-Based Display Technology; Texas Instruments
DLP Integrated Circuit
Source: http://www.asme.org/Communities/History/Landmarks/53_Digital_Micromirror_Device.cfm
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]
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
Switching ResponseThree 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
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
Bias Voltage Compensation
Source: Begon Martin, Ciapala Richard, Deaki Zoltan; “Reliability of MEMS: Case Study”; Ecole Polytechnique Federale De Lausanne
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
Hinge Memory Lifetime
Source: Michael R. Douglas; “DMD reliability: a MEMS success story”; Texas Instruments
History
• Developed by Texas Instruments (TI) [2]
• DOD initially funded TI to develop a light modulator [2]
• Project Team Leader: Dr. Larry Hornbeck [2]
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
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
Web Links and Other Information1. Texas Instrument’s Official DLP Site: http://www.dlp.com/2. Flash Demo of DLP: http://www.dlp.com/includes/demo_flash.aspx3. http://en.wikipedia.org/wiki/Digital_micromirror_device4. http://www.audioholics.com/education/display-formats-technology/display-
technologies-guide-lcd-plasma-dlp-lcos-d-ila-crt/display-technologies-guide-lcd-plasma-dlp-lcos-d-ila-crt-page-2
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
References1. What is DLP?,; http://focus.ti.com/dlpdmd/docs/dlplearningdetail.tsp?sectionId=62&tabId=22492. “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.cfm3. Gary A. Feather, David W. Monk; “The Digital Micromirror Device for Project Display”; 1995 International Conference on
Wafer Scale Integration4. Larry J. Hornbeck; “Current Status of Digital Micromirror Device (DMD) for Projection Television Applications”, 19935. Larry J. Hornbeck; “Digital Light Processing: A New MEMS-Based Display Technology”; Texas Instruments6. Lars A. Yoder; “An Introduction to the Digital Light Processing (DLP) Technology”; Texas Instruments7. Dana Dudley, Walter Duncan, John Slaughter; “Emerging Digital Micromirror Device (DMD) Applications”; Texas
Instruments8. Begon Martin, Ciapala Richard, Deaki Zoltan; “Reliability of MEMS: Case Study”; Ecole Polytechnique
Federale De Lausanne
9. Michael R. Douglas; “DMD reliability: a MEMS success story”; Texas Instruments