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A MEMS Design Project Debby Chang, Randall Evans, Caleb Knoernschild under Jungsang Kim, Ph.D.

A MEMS Design Project Debby Chang, Randall Evans, Caleb Knoernschild under Jungsang Kim, Ph.D. December 10, 2005 Duke University. Overview. Design overview First Test: manual movement of the gear Design of gears Test setup for gears Test requirements for gears Test results for gears

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A MEMS Design Project Debby Chang, Randall Evans, Caleb Knoernschild under Jungsang Kim, Ph.D.

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  1. A MEMS Design Project Debby Chang, Randall Evans, Caleb Knoernschild under Jungsang Kim, Ph.D. December 10, 2005 Duke University

  2. Overview • Design overview • First Test: manual movement of the gear • Design of gears • Test setup for gears • Test requirements for gears • Test results for gears • Second Test: manual actuation of the mirror • Design of the mirror • Test setup for mirror • Test requirements for mirror • Test results for mirror • Final Test: actuation of comb drives • Design of comb drive • Test setup for comb drive • Test requirements for comb drive • Test results for comb drive

  3. Design Overview

  4. Design Overview

  5. Design Overview Backside View

  6. Design Overview y x

  7. Systems • 3 Subsystems • Linear Actuator • Gears and Ratchet • Mirror and Mirror Arm

  8. Overview • Design overview • First Test: manual movement of the gear • Design of gears • Test setup for gears • Test requirements for gears • Test results for gears • Second Test: manual actuation of the mirror • Design of the mirror • Test setup for mirror • Test requirements for mirror • Test results for mirror • Final Test: actuation of comb drives • Design of comb drive • Test setup for comb drive • Test requirements for comb drive • Test results for comb drive

  9. Error 1 • The large gear is not anchored! Missing Anchor Anchor “Where are the big gears??”

  10. Gear Test • Does the gear perform its function when manually stimulated. • Procedure: stimulate the gear by placing a probe against one of the teeth, then pushing tangentially

  11. Testing-Materials • Micromanipulator with a glass pipette probe mounted vertically • 100x+ camera capable of recording video • light source mounted vertically

  12. Gear Test Result

  13. Overview • Design overview • First Test: manual movement of the gear • Design of gears • Test setup for gears • Test requirements for gears • Test results for gears • Second Test: manual actuation of the mirror • Design of the mirror • Test setup for mirror • Test requirements for mirror • Test results for mirror • Final Test: actuation of comb drives • Design of comb drive • Test setup for comb drive • Test requirements for comb drive • Test results for comb drive

  14. Mirror and Mirror Arm y x

  15. Mirror Design • SEM Image + Coventor Design

  16. Test Procedure • First test: Measure angle change based upon translation

  17. Top “stop” .5 um gap Bottom “stop” Error? • Mirror flaw in the connection of the mirror arm to mirror. The top stopper has a .5um gap. • Still Connected! (most of the time)

  18. Error 2 • No release holes were designed into a large planar mirror, so the first three chips, released in HF for 4 minutes, may not have fully released the mirrors • To overcome this, we released 2 extra devices for a total of 15mins in HF to ensure complete release • One device that was released flipped over onto the gel (see backside picture)

  19. First Release Results

  20. Second Release Results

  21. Mirror Fracture Strength • Fracture Strength of Polysilicon =1.55 GPa (LaVan et. al ) • Cross sectional area of one mirror arm A = WxD= 3um * 1.5 um = 4.5 e-12 m^2 • Force required to break the mirror arms F=Fracture Strength/2*Area F= 0.014N • Mirror Weight = 1.1 e-9 kg = 1.1e-8N A =Cross Sectional Area “Size and Frequency of Defects in ” LaVan et. Al.

  22. Broken Arms

  23. Mobile mirror release problems

  24. Overview • Design overview • First Test: manual movement of the gear • Design of gears • Test setup for gears • Test requirements for gears • Test results for gears • Second Test: manual actuation of the mirror • Design of the mirror • Test setup for mirror • Test requirements for mirror • Test results for mirror • Final Test: actuation of comb drives • Design of comb drive • Test setup for comb drive • Test requirements for comb drive • Test results for comb drive

  25. y x Design of Comb Drive

  26. Design of Comb Drive • Expectations • Designed to move 20 um at 40 Volts, BUT … • Flaw only allows ~ 14 um movement • Hope to see 14 um movement ~14um

  27. Test setup for Comb Drive • DC Characteristics • Apply a DC voltage and observe movement under microscope or camera • Use feature sizes of components on device to estimate the comb drive movement • AC Characteristic • Test varying voltages and frequencies • view under microscope or camera to observe motion • Look for movement of drive – resonance frequency occurs at largest drive displacement response

  28. Comb Movement and Elasticity

  29. Test Requirements for Comb Drive • Microprobe tip • For DC Characterization • 120 Volt, 2.5 Amps Power supply • Microscope • CCD viewing equipment • For AC Characterization • 5 Vpp max function generator • 10x amplifier • Microscope • CCD viewing equipment

  30. Test Results for Comb Drive • Tests were not successful due to several design errors • Contact Pad Flaw • Comb Tooth Motion due to Poly 0 ?

  31. Error 3 • Ground Electrode electronically isolated from poly 0 wire • Poly 1 pattern placed inside Anchor 1 Probe

  32. Contact Pad Substrate Poly 0 Poly 0 Substrate

  33. Contact Pad Substrate Poly 0 Oxide 1 Oxide 1 Poly 0 Substrate

  34. Contact Pad Substrate Poly 0 Oxide 1 Poly 0 Substrate

  35. Contact Pad Substrate Poly 0 Oxide 1 Poly 1 Poly 1 Poly 0 Substrate

  36. Contact Pad Substrate Poly 0 Oxide 1 Poly 1 Poly 1 Poly 0 Substrate

  37. Contact Pad Substrate Poly 0 Oxide 1 Poly 1 Oxide 2 Oxide 2 Poly 1 Poly 0 Substrate

  38. Contact Pad Substrate Poly 0 Oxide 1 Poly 1 Oxide 2 Poly 1 Poly 0 Substrate

  39. Contact Pad Substrate Poly 0 Oxide 1 Poly 1 Oxide 2 Poly 2 Poly 2 Poly 1 Poly 0 Substrate

  40. Contact Pad Substrate Poly 0 Oxide 1 Poly 1 Oxide 2 Poly 2 Poly 2 Poly 1 Poly 0 Substrate

  41. Contact Pad Substrate Top View Poly 0 Oxide 1 Poly 1 Oxide 2 Poly 2 Poly 2 Poly 1 Poly 0 Substrate

  42. Error 4 • Free comb seems to be driven to substrate instead of driven to engage more with corresponding teeth. • Movable inner comb does not move horizontally very much

  43. Comb Teeth Design Flaw • Comb drive does not move as designed because of Poly 0 • Poly 0 layer leaks charge to nitride layer which forces movable teeth into the substrate C1 C1 C2 C1 C1 C1 C1 But there are twice as many C2 capacitances C2 C2 ++++++++++++++++++++++++++++++++++++++++++++++++

  44. Comb Teeth Design Flaw L L is intersecting teeth length w2 Ground h w1 do

  45. Comb Teeth Design Flaw L is intersecting teeth length w2 Ground h-Δ w1 do-Δ

  46. Comb Teeth Design Flaw • Possible temporary solution – reduce built up charge by grounding substrate through package and silicon paste

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