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Silicon-on-Insulator Microassembly

Silicon-on-Insulator Microassembly. Matthew Last Dissertation Talk December, 2005. Smart Dust. Pister’s vision: Millimeter-scale robots Power Computation Communication Sensing Mobility. Previous Small System Assembly. Integrated SALT Laser Diode Ball Lens 2-axis Micromirror

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Silicon-on-Insulator Microassembly

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  1. Silicon-on-Insulator Microassembly Matthew Last Dissertation Talk December, 2005

  2. Smart Dust • Pister’s vision: Millimeter-scale robots • Power • Computation • Communication • Sensing • Mobility

  3. Previous Small System Assembly • Integrated SALT • Laser Diode • Ball Lens • 2-axis Micromirror • Milli-scale assembly • Micro-scale assembly • Performance • Poor alignment • Poor mirror specs … Thus began a 3-year-long wrong turn

  4. SOI Microassembly • Goal: Build Micromirrors and Micro-robots • Problem: Process complexity • Yield • Speed • Method: Simplify wafer-level processing • Simplest process: Single-mask, Deep Reactive Ion Etch (DRIE) in Silicon On Insulator (SOI) wafer

  5. Prepare surface, oxidize wafers • Wafers by the batch

  6. Bond wafers, anneal, inspect

  7. Grind/polish Device layer Buried Oxide Handle Wafer

  8. Litho • Wafer-level

  9. Etch

  10. Protect, Dice

  11. Clean, release oxide, CPD • Chip-level

  12. Anti-stiction treatment • Cr (6nm) + Au (30nm) • Self-Assembled Monolayer (FDTS) coating

  13. But I need more layers! • Out-of-plane motion • Z-axis • Rotation • Multiple layers of electrical/mechanical interconnect • Sliders, bearings, gears, hinges, etc • Answer: Assemble device from multiple parts

  14. Serial Pick and Place • Advantages • Quick • Fastest to date: 30hr design cycle • Simple • Manufacturable • Customizable • Disadvantages • Expensive • Linear scaling

  15. Other Microassembly • Micro-tweezers - Keller • Micro-assembly – Shimada, Fearing • Pick and Place assembly – Dechev, Mills • SOI Microassembly – Zyvex

  16. Pick and Place – Overview • Grasp part • Break tether • Rotate part 90o • Carry it to assembly location • Place it into socket • Let go of part

  17. Assembling parts – Handling parts 1

  18. Assembling parts – Handling parts 2 E. Shimada, J.A. Thompson, J. Yan, R.J. Wood and R.S. Fearing, "Prototyping Millirobots using Dextrous Microassembly and Folding," Proc. ASME IMECE/DSCD, Orlando Florida, November 5-10, 2000 • Ortho-Tweezers • Compliant Ortho-grippers

  19. Redesign: Sidewall Orthogrippers • Removes need for thick buried oxide part part part part part part (c) (a) (b) part part part part (d) (e)

  20. Assembling parts – Connectors • Purpose of connection • Electrical • Mechanical • Optical, fluidic, etc. • Connector goals • Sub-micron positioning of part • Overcoming part/assembly tolerances • Maximization of pullout forces • Minimization of insertion forces • Load-bearing ability • Electrical/thermal connectivity • Our work: Optimize mechanical and electrical connection

  21. Snap Lock Connector

  22. Single-axis out-of-plane rotator 1 Electrostatically-actuated rotation platform (4.2o to date)

  23. Single-axis out-of-plane rotator 2 Electrostatically-actuated rotation platform (17o to date)

  24. 2-axis rotation stage • Stationary end in snap lock • Moving end attached to XY stage Moving clamp

  25. Drawbacks of Snap Lock Connector • Pull-out force • Play

  26. Clamp Connector

  27. Pull-out Force Tests

  28. Contact Resistance of Clamp Connection Contact resistance varies from 20-60 (gold-coated structures and contacts)

  29. Optimized 2-axis Rotation Stage • Designed for large DC deflection • Minimization of assembly steps • Rotator separate from reflector

  30. Operating Principle • Use torsion and bending modes of beams • Conversion of in-plane motion to out-of-plane motion via moment arm connecting beams

  31. Angle vs Force • Large deflections, small forces • Negligible cross-axis coupling

  32. Drawback: Bounce mode • Lowest-frequency mode is a z-axis bounce mode. • Does not couple into rotation at zero deflection • Worst-case scenario: 1 spot deflection at 6g acceleration (1mm diameter, 20um-thick mirror) From ANSYS:

  33. As fabricated Assembled

  34. Range of Motion • Part assembled, pushed with probe tip Total angle: 16.5 degrees Total angle: 12 degrees

  35. Actuated rotation stage • 4 single-axis actuators (+/- X, +/- Y) • Fully-suspended clamps

  36. Test data • To date: One quadrant working (+x, +y) • Predicted max values: 28 degrees (flex), 26 degrees (tors) 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

  37. Summary • Radical simplification of process: • 1 mask, 1 etch, release • Design for microassembly • Part handling methodology (tethers, handles) • Sockets for electrical and mechanical interconnect • Tooling for microassembly • Key innovation: micromachined passive rotation stage • Capable devices • 1- and 2-axis rotation stages

  38. Future Research Areas • Automation • Simplicity, Speed, Reliability • Process extensions • More capable assembled parts • Device Optimization/Scaling • Better actuators, springs • Further performance gains • Reliability • Long-term stability of clamps

  39. Combination with Smart Dust • Walking/hopping robots • Steered micro-rockets W.Lindsay, et al. Thrust and Electrical Power from Solid Propellant Microrockets S Bergbreiter, Qualifying Exam

  40. Conclusion • Assembly extends range of devices one can build in a single-mask process • Serial Pick-and-place assembly • Fast • Flexible • Effective

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