Lecture 20 Optical MEMS (2)

Transcription

1 EEL6935 Advanced MEMS (Spring 2005) Instructor: Dr. Huikai Xie Lecture 20 Optical MEMS (2) Agenda: MOEMS Introduction Micromirrors EEL6935 Advanced MEMS 2005 H. Xie 3/30/ Optical MEMS Topics Introduction to MOEMS Optical bench on chip; Smart dust; Optical communications Optical MEMS Devices Reflective Micromirrors Refractive Microlenses Microprisms Diffractive Microgratings Microlenses (Fresnel) Waveguides Interference-based Filters Tunable VCSELs Microspectrometers Uncooled Infrared Detectors Photonic crystals MEMS-based Optical Imaging EEL6935 Advanced MEMS 2005 H. Xie 2

2 Today s Topic Introduction to MOEMS Optical bench on chip Smart dust Optical communications Electrostatic mirrors Parallel-plate Vertical comb drives Lateral comb drive with a vertical lever Fabrication Processes Thin-film Bulk silicon Assembly Integrated EEL6935 Advanced MEMS 2005 H. Xie 3 Optical Bench On Chip Developed by Prof. M. Wu s group at UCLA EEL6935 Advanced MEMS 2005 H. Xie 4

3 Optical Bench On Chip LG Electronics Institute of Technology EEL6935 Advanced MEMS 2005 H. Xie 5 Tunable Optical Transmitter Hybrid Integration EEL6935 Advanced MEMS 2005 H. Xie 6

4 Smart Dust mirror Sensor Detector/Receiver Solar Cell 1.2mm K. Pister s group (UC-Berkeley) EEL6935 Advanced MEMS 2005 H. Xie 7 Smart Dust A self-contained, millimeter-scale sensing and communication platform for a massively distributed sensor network. This device will be around the size of a grain of sand and will contain sensors, computational ability, bi-directional wireless communications, and a power supply, while being inexpensive enough to deploy by the hundreds. Potential Applications: Weather/seismological monitoring on Mars Internal spacecraft monitoring Land/space comm. networks Chemical/biological sensors Weapons stockpile monitoring Defense-related sensor networks Product quality monitoring P. B. Chu et al., MEMS 1997 EEL6935 Advanced MEMS 2005 H. Xie 8

5 Wireless Sensor Network Wireless Sensor Node (Sensor + Mote) Cell Phone or Wi-Fi Storage Base Station Environmental Sensors Radio Mesh Networks Crossbow Technology, Inc. Indoor/Outdoor Environmental Monitoring Security and Tracking Health and Wellness Monitoring Power Monitoring Inventory Location Awareness Factory and Process Automation Seismic and Structural Monitoring Training and Systems Integration EEL6935 Advanced MEMS 2005 H. Xie 9 Micromirrors: Electrostatic Electrostatic Micromirrors Parallel-plate Vertical comb drive Lateral comb drive with vertical conversion Fabrication Processes Thin-film Bulk silicon Assembly Integrated EEL6935 Advanced MEMS 2005 H. Xie 10

6 Parallel-Plate Electrostatic Micromirrors Texas Instruments Digital Micromirror Devices (DMD) Lucent Technologies 2D Micromirror Easy Implementation Tradeoffs: Rotation angle; size; drive voltage EEL6935 Advanced MEMS 2005 H. Xie 11 Electrostatic Micromirrors Vertical comb drives Comb fingers with multiple conductor layers Carnegie Mellon Univ. Curled-hinge comb drives Carnegie Mellon Univ. Univ. of Florida SOI-based staggered comb drives UC-Berkeley Stanford Univ. UC-Davis Photoresist reflow UCLA Others EEL6935 Advanced MEMS 2005 H. Xie 12

7 Vertical Comb Drive-1 Curled-Hinge Comb Drive: Concept H. Xie and G.K. Fedder, ASME International Mechanical Engineering Congress and Exposition, New York, NY, Nov , 2001 EEL6935 Advanced MEMS 2005 H. Xie 13 Curled-Hinge Comb Drive: Mirror Design Vertical Comb Drive-1 EEL6935 Advanced MEMS 2005 H. Xie 14

8 Vertical Comb Drive-1 Curled-Hinge Comb Drive: Analytical Analysis F z N dc 2 N 1 = V = 2 dz 2 l cos α dc 2 V dα A( α ) = zol = z + z + z z 2 tan ( ) ( ) ( θ α 2 tan θ α )2 C ( α ) ε0 A = g ( α ) H. Xie et al, Journal of MEMS, EEL6935 Advanced MEMS 2005 H. Xie 15 Vertical Comb Drive-1 Curled-Hinge Comb Drive: Analytical Analysis The rotation saturates after certain drive voltage But maximum angular rotation can be increased by using thicker comb fingers Placing the comb drives closer to the rotational axis can increase the maximum rotation angles. EEL6935 Advanced MEMS 2005 H. Xie 16

9 Vertical Comb Drive-1 Curled-Hinge Comb Drive: Fabricated Mirror anchor + V - Z-actuator F 1A 1B 2B 2A 1A 1B 2B 2A F + V - anchor 1mm x 1mm mirror Radius of curvature: 50 mm Curled combs designed to obtain bi-directional rotation Comb pairs placed to achieve differential torque and cancel z displacement Z-actuators included to adjust z-motion EEL6935 Advanced MEMS 2005 H. Xie 17 Vertical Comb Drive-1 Curled Comb Drive Comb Finger Ends Metal-1 mesh Rotor fingers 5.0µm 40µm Stator fingers Static Response Frequency Response Tilt Angle (degree) Displacement (m) θ y z Voltage (V) Frequency (Hz) EEL6935 Advanced MEMS 2005 H. Xie 18

10 Staggered Comb Drive Vertical Comb Drive-2 Silicon wafer-to-wafer bonding Single-crystal silicon based micromirror Flat Large size: 550µm diameter Large angular deflection: Optical scan angle of 24.9º at its 34 khz resonant frequency R. Conant et al. (UC-Berkeley), Hilton Head 2000 EEL6935 Advanced MEMS 2005 H. Xie 19 Vertical Comb Drive-3 Angular Comb Drive Actuator Photoresist reflow Patterson et al (UCLA), OFC 2002 EEL6935 Advanced MEMS 2005 H. Xie 20

11 Post-MUMPs DRIE process Vertical Comb Drive-4 Post-MUMPs process Backside DRIE etch Wet etch (BHF) for release Single-crystal silicon structures Manually assemble the tilt fingers using latches Mirror diameter: 1mm Mirror radius of curvature: 40cm +/-6 at 55 V d.c. Piyawattammetha et al (UCLA), OFC 2003 EEL6935 Advanced MEMS 2005 H. Xie 21 Buckled Comb Drive Vertical Comb Drive-5 Vertically buckled bridge Wet etch SiO2 Poly-Si as HF etching mask Sasaki et al (Tohoku U.), JMEMS, vol.13 (2004) EEL6935 Advanced MEMS 2005 H. Xie 22

12 Electrostatic Micromirrors Lateral Comb Drives Hinges Sandia UC-Berkeley UCLA Vertical levers UC-Berkeley EEL6935 Advanced MEMS 2005 H. Xie 23 Lateral Comb Drive -1 Hinged Thin-film Micromirror (Sandia National Lab.) Micromirror and Drive Mechanism Gear Speed Reduction Unit EEL6935 Advanced MEMS 2005 H. Xie 24

13 Lateral Comb Drive -2 SOI Micromirror SOI wafer DRIE Si etch LPCVD Si3N4 for anchors Light-weight SOI MEMS Mirror LPCVD poly-si Oxidize poly-si CMP LPCVD poly-si Si DRIE RTA 750~900 C to form tensile stress HF release Supercritical drying J.T. Nee et al (UC-Berkeley, MEMS 2000 EEL6935 Advanced MEMS 2005 H. Xie 25 Lateral Comb Drive-3 Multilevel Beam Microstructures Torsional Mirror Concept Vertical Comb- Drive Mirror Lixia Zhou et al V. Milanovic et al, JMEMS, vol.13 (2004) EEL6935 Advanced MEMS 2005 H. Xie 26

14 Multilevel Beam Fabrication Torsional Micromirror Lateral Comb Drive-3 Flat Lightweight High speed Low power Electrostatic actuation V. Milanovic et al, JMEMS, vol.13 (2004) EEL6935 Advanced MEMS 2005 H. Xie 27 Summary Brief introduction of MOEMS Discussed different types of electrostatic micromirrors Parallel-plate Small sizes/small angles Vertical comb drives Large angle; large size; good flatness But more complicated fabrication Lateral comb drives Large angle; large size; good flatness Complicated fabrication EEL6935 Advanced MEMS 2005 H. Xie 28