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					        Highly Adaptable MEMS-Based Display
              with Wide Projection Angle

Veljko Milanović, Kenneth Castelino, Daniel T. McCormick

               Adriatic Research Institute
     828 San Pablo Ave., Ste. 109, Berkeley, CA 94706

                  MEMS 07’ p 143~146




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Outline




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MEMS-BASED DISPLAY

     Two Basic MEMS-based projection display :
     Reflective displays,pioneered by Texas Instrument
     Diffractive display,pioneered by Silicon Light Machines
          large deflection angles
          large displacement




                                                         3
                                      Research Chart Analysis
                                                            Year
                         2000         2001      2002      2003      2004     2005      2006    2007
    DRIE Devices
    tunable field emission devices (FEDs).
Torsional Micromirrors Lateral Actuators
                Sunghoon , Two-Axis
                                [4]Single axis rotation
                                 [15] Two-Axis Scanners
                      [7] 2 DoF linkages to a central stage.
   [14] 3 DoF With Large Static Rotation and Piston Actuation
                            Fully-Functional (high-speed /low-power)
                                 Large rotation with contact to neighboring elements

                                                                   Display with Wide angle
                                         [18] Improve image quality/re-flesh rate/brightness
                                                                 High Temperature Operation
                                        Production Engineering
                                                                                                      4
                                                                           Veljko Milanovic´, Member, IEEE
                      A Brief History (1)
       Year Publish                           Contribution
 [1] 2000 (Journal ) DRIE Devices were fabricated on silicon-on-insulator (SOI) wafers

 [2] 2000 (Journal ) Integration of optimized microelectromechanical systems (MEMS) in RF systems on
                      substrates such as sapphire, GaAs, and even CMOS.

 [8] 2001 (Conf.)      Integration of a wide variety of SOI-MEMS sensors, actuators and micromirrors. 1-axis mirror

 [9 ] 2001 (Conf.)     The micromirror structures are laterally electrostatically actuated, torsionally suspended
                        micromirrors with static scanning deflection of over 40° peak-to-peak optical angle.

 [10] 2001 (Conf.)     Enabling additional independent degrees of freedom of operation: both upward and downward
                        vertical pistoning motion as well as bi-directional rotation.

 [3] 2001 (Journal ) Utilize MEMS actuators to laterally adjust electrode distances.

 [11] 2002 (Conf.)     Add vertical combdrives. + new beam structure which decreases lateral movement while
                        enabling rotation.

 [12] 2002 (Conf.)    Providing 1DoF and 2DoF rotation of micromirrors ; static optical deflection from –20° to +19°

 [4] 2003 (Journal ) Laterally electrostatically actuated, torsionally suspended (SOI) micromirrors with a static
                      optical deflection angle of over 40 peak-to-peak.

 [13] 2003 (conf.)     Allow larger static rotations of the micromirror from the combdrive-stroke limited rotation
                        The static optical deflection of the x-axis up to 9.6° and of the y-axis up to 7.2°, are achieved
                        for <275 Vdc ; lower-voltage operation exhibits static optical deflection about the x-axis to
                        10.8° and about the y-axis to 11.7°, for <85 Vdc.                                                 5
                                                                              Veljko Milanovic´, Member, IEEE
                      A Brief History (2)
      Year Publish                            Contribution
 [5] 2004 (Journal ) vertical comb drives micromachined from the back side and front side of a 50- μm silicon-
                      on- insulator device layer.

 [6] 2004 (Journal ) larger static rotations of the micromirror from the comb-drive

 [7] 2004 (Journal ) high aspect ratio silicon-on-insulator microelectromechanical systems (SOI-MEMS) by
                      enabling additional independent degrees of freedom of operation: both upward and
                      downward vertical pistoning motion as well as bi-directional rotation

[14] 2004 (conf.) Each actuator can rotate bi-directionally to raise or lower its linkage,giving the stage the required
                    (3 DoF. )

 [15] 2004 (conf.) Tip-Tilt-Piston Actuators for High Fill-Factor Micromirror Arrays, (3 DoF)

 [19] 2004 (joural) Tip-tilt-piston actuators for high fill-factor micromiror arrays
 [16] 2006 (conf.) 95% - chosen such that the mirrors would have sufficient space for large rotations without making
                     contact to neighboring elements.

 [17] 2007 (conf.) display system with a very wide projection angle of up to 120°.

 [18] 2007 (conf.) To improve image quality, reflesh rate, brightness . Horizonal axis resonant frequencies ranging
                    from 10 kHz to 21.5 kHz for mirror sizes ranging from 1.2mm to 0.8 mm




                                                                                                                           6
                         Basic Manufacture Process
                   Deep reactive ion etch (DRIE) [1]
The biggest obstacle in SOI-MEMS mirrors is the
                                                four-mask process layers with DRIE:
inherent lack of out-of-plane motion.,[2001]
                                                two for front-side and two for back-side
                                                 etching.
                                                 High layers(50 μm)      Three -level
                                                Lower layers(30 μm)      Vertical Comb
                                                Upper layers (30 μm)
                                                Backside opening
                                                  releases large areas for out-of plane
                                                   motion and rotation of micro mirrors.
                                                  up and down-actuating comb drives




                                                                                       7
                  Single axis rotation




                           Problem:
                           radius of curvature,
                                                          50V  100 angle
                           dynamic deflection,
Laterally actuated ,2001
                           Bucking

                                        providing 1DoF (or single-axis) rotation
                                        out-of-wafer-plane degrees of freedom
                                         (DoF).
                                        high aspect ratio

                           up-actuating comb drives
                                                               Rotor & Stator
Vertical actuated ,2003    down-actuating comb drives
                                                               2 x 2=4 Types

                                                                                    8
Problem:
radius of curvature
                                    Two axis rotation-Vertical,island
bending




                                                                                       x rotating

                                                             Y rotating




                                                                   vertical comb drives
                                                                    Isolation island
                                                                    upper-comb and Lower-Comb
                                                                    x rotating + Y rotating
          Type 1- vertical combdrives ,2002

        A High Aspect Ratio 2D Gimbaled Microscanner with Large Static Rotation,2002
                                                                                                    9
               Two axis rotation-Vertical,rotation transformer
                                                                    2 generation




                                                            Comb drive
                                                             single-axis+ single-axis
                                                             unidirectional rotation


                                                          Rotation transformer Mechanism



                                                                low voltage
    Type 2- vertical combdrives ,2004                           large displacement
Veljko Milanović, Int. Conf. on Microelectromechanical Systems, MEMS2004                   10
                             3 generation( Three axis rotation)
     3 DoF tip-tilt-piston actuators                     Stator                    Rotor




    Linkage + Rotation transformer




[19 ]D. T. McCormick, 2004 Solid State Sensor,Actuator and Microsystems Workshop           11
                            Micromirrors fully assembled
                            1.2mm




     Backside silicon micromirrors                   four vertical combdrive rotators




            fully assembled                         four elements being driven by the software
[16] D. T. McCormick ,2006 IEEE/LEOS Optical MEMS                                                12
Summary

 A. Specification Achieved :
  3-level selective DRIE process SOI Wafer
  low-inertia mirror-apertures 1 mm x 1 mm
  rotations of the micromirror from 20° of peak-to-peak optical deflection
  maximum displacement of -12 μm to 12 μm
  125 μm stand-off pedestal
  15 μm thickness( metalized with a 100 nm thick layer of Al)
 B. The important Milestone & Contribution history




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C. Key fabrication     process presented in this work
All combfingers are fabricated isolated and independently      DRIE

Vertical combdrive sets        large displacement

 Comb-fingers is controlled several μm of overlap

 Masks for etching of comb-fingers are self-aligned by a single mask

 The process requires selective, high aspect ratio multilevel etching,
    Etch time is very important




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                                              Referance(1)
[1] V. Milanović, L. Doherty, D. Teasdale, C. Zhang, V. Nguyen, M. Last, and K.Pister, "Deep Reactive Ion
Etching for Lateral Field Emission Devices," IEEE Electron Device Letters, vol. 21, no. 5, May. 2000.

[2] V. Milanović, M. Maharbiz, and K. Pister, "Batch Transfer Integration of RF Microrelays," IEEE Microwave
and Guided Wave Letters, vol. 10, no. 8, pp. 313-315, Aug. 2000.

[3] V. Milanović, L. Doherty, D. Teasdale, S. Parsa, C. Zhang, and K. Pister, "Micromachining Technology for Lateral Field
Emission Devices," IEEE Tran. On Electron Devices - special issue on vacuum electronics, vol. 48, no. 1, pp.166-173, Jan.
2001.

[4] V. Milanović, M. Last, K.S.J. Pister, "Laterally Actuated Torsional Micromirrors for Large Static Deflection," IEEE
Photonics Technology Letters, vol. 15, no. 2, pp. 245-247, Feb. 2003.

[5] V. Milanović, S. Kwon, L. P. Lee, "High Aspect Ratio Silicon Micromirrors with Large Static Rotation and Piston
Actuation," IEEE Photonics Technology Letters, vol. 16(8) , Aug. 2004, pp. 1891 - 1893.

[6 ]V. Milanović, D. T. McCormick, G. Matus, "Gimbal-less Monolithic Silicon Actuators For Tip-Tilt-Piston Micromirror
Applications," IEEE J. of Select Topics in Quantum Electronics,Volume: 10 , Issue: 3 , May-June 2004, Pages:462 – 471

[7 ]V. Milanović, "Multilevel-Beam SOI-MEMS Fabrication and Applications,“ IEEE/ASME Journal of
Microelectromechanical Systems, vol. 13, no. 1, pp. 19-30, Feb. 2004.

[8 ]V. Milanović, M. Last, K.S.J. Pister, "Torsional Micromirrors with Lateral Actuators,” Trasducers'01 - Eurosensors XV
conference, Muenchen, Germany, Jun. 2001.

[9 ]V. Milanović, M. Last, K.S.J. Pister, "Monolithic Silicon Micromirrors with Large Scanning Angle,” Optical MEMS 2001,
Okinawa, Japan, Sep. 2001.

[10] V. Milanović, “Multilevel-Beam SOI-MEMS for Optical Applications,” Proc. 9th IEEE Int. Conf. on Electronics, Circuits
and Systems - ICECS'02, Dubrovnik, Croatia, Sep. 2002. pp. 281-215

                                                                                                                             15
                                               Referance(2)
[11] V. Milanović, L. Doherty, “A Simple Process for Lateral Single Crystal Silicon Nanowires,” to be presented, Int.
Mechanical Eng. Conf. And Exhibit IMECE'02, New Orleans, LA, Nov. 2002.

[12]V. Milanović, S. Kwon, L. P. Lee, “Monolithic Vertical Combdrive Actuators for Adaptive Optics,” IEEE/LEOS Optical
MEMS 2002, Lugano, Switzerland, Aug. 2002.

[13] V. Milanović, G. Matus, T. Cheng, B. Cagdaser, “Monolithic High Aspect Ratio Two-axis Optical Scanner in SOI,” Int.
Conf. on Microelectromechanical Systems, MEMS2003, Kyoto, Japan, pp. 255-258, Jan. 2003.

[14] V. Milanović, G. Matus, D. T. McCormick, “Tip-Tilt-Piston Actuators for High Fill-Factor Micromirror Arrays," at the
Hilton Head 2004 Solid State Sensor, Actuator and Microsystems Workshop, Hilton Head, SC, Jun. 6-10, 2004.

[15] V. Milanović, K. Castelino, “Tip-Tilt-Piston Actuators for High Fill-Factor Micromirror Arrays,”
Solid State Sensor, Actuator and Microsystems Workshop, Hilton Head, SC, Jun. 6-10, 2004.


[16] Veljko Milanović, Kenneth Castelino, Daniel McCormick, “Fully-Functional Tip-Tilt-Piston Micromirror Array," 2006
IEEE/LEOS Optical MEMS and Their Applications Conf., Big Sky, Montana, Aug. 21, 2006.

[17]Veljko Milanović, Kenneth Castelino, Daniel McCormick, “Highly Adaptable MEMS-based Display with Wide Projection
Angle," 2007 IEEE Int. Conf. on Microelectromechanical Systems (MEMS'07), Kobe, Japan, Jan. 25, 2007.

[18] Veljko Milanović, “Improved Control of the Vertical Axis Scan for MEMS Projection Displays ," submitted to: 2007
IEEE/LEOS Optical MEMS and Their Applications Conf., Hualien, Taiwan, Aug. 12, 2007.




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Thank you for your attention!




                                17
                             Appendix

 MEMS Dewvices
 Fish eye wide-angle lens
 optical scan angle 128o




                                        18
                                Appendix
Adriatic Research Institute

ARI Services :
 Custom Microfabrication Services
  (1) 4” and 6” Wafers for CMOS and MEMS
  (2) Diffusion ,Oxidatin, Depostion
  (3) Etching
      a. DRIE
      b. RIE
      c. Plasma Etching
      d. XeF2 Etching
   (4) E-Gun for W, Al, Cr, Au
 Consulting
  CMOS and MEMS with 6 years experiences
 Contract Research and Development


  ARI Micromirror Development(MPG FilE) :


                                            19
                                     Transformer rotations




         The transformers allow larger static rotations of the micromirror



IEEE JOURNAL OF SELECTED TOPICS IN QUANTUM ELECTRONICS, VOL. 10, NO. 3, MAY/JUNE 2004

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