Digital Micromirror Devices (DMD) ECE 5320 – Mechatronics Utah State University Brett Rogers brett.rogers@aggiemail.usu.edu

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: 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

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 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

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 Information Texas Instrument’s Official DLP Site: http://www.dlp.com/ Flash Demo of DLP: http://www.dlp.com/includes/demo_flash.aspx http://en.wikipedia.org/wiki/Digital_micromirror_device 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

References What is DLP?,; http://focus.ti.com/dlpdmd/docs/dlplearningdetail.tsp?sectionId=62&tabId=2249 “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