Digital Micromirror Devices (DMD) ECE 5320 – Mechatronics Utah State University Brett Rogers [email protected]

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


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


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


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


Mirror Affected by Hinge Memory

Front mirrors are perfectly horizontal, while rear mirrors maintain a residual tile due to hinge memory.


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

Documents

Digital Micromirror Devices (DMD) ECE 5320 – Mechatronics Utah State University Brett Rogers [email protected]