Report presentation on project work involving the fabrication and characterization of a MEMS Bi/Multi-Stable Optical In-plane Switch, for the Micro-Elcectro Mechanical Systems (MEMS) course, in the Nanotechnology MSc program at the Information and Telecommunication (ICT) school KTH.

1. Bi/Multi-Stable Optical In-
Plane Switch
Hands-On Microelectromechanical Systems Engineering
Sumit Mohanty
Spandan Dey
Ahmed AlAskalany

2. Design and COMSOL Simulations
• Main actuator
• Restoration mechanism

3. Main Actuator Designs
Requirements:
• 30um of in-plane movement
• Maximum actuation voltage of
65V

4. Main Actuator Designs: Comb Drive
• 100 fingers
• Finger width is 4um
• Finger spacing is 3um
• Simulated force is 26uN
• Unidirectional 30um in-plane
movement

5. Main Actuator Designs: Double Comb Drive
• 100 fingers
• Finger width is 4um
• Finger spacing is 3um
• Simulated force is 26uN
• Bidirectional 15um in-plane
movement

6. Main Actuator Designs
• 25 fingers on each drive
• Finger width is 4um
• Finger spacing is 3um
• Simulated force is 15uN at 30V
• Bidirectional 15um in-plane
movement

7. Restoring Mechanisms: Folded Spring

8. Restoring Mechanisms: Folded Spring

9. Restoring Mechanisms: Folded Spring

10. Restoring Mechanisms: Folded Spring

11. Locking Mechanisms: Interdigitated
• Normally locked by spring
• Unlocked by actuated comb
drives
• Step=Locking finger width +
spacing

12. Locking Mechanisms: Graded
• Normally locked by spring
• Unlocked by actuated comb
drives
• Step=Minimum feature size

13. Locking Mechanisms: Parallel Plate
• Normally locked
• Unlocked by applying different
voltage to inner plates

14. Designs
• 4 variants

15. Characterization
• Design A
• Design B
• Design C
• Design D

16. Design A (Comb drive based lock)

17. Design A: Lateral instability
• Two actuators
• One restoring spring
Lateral instability
Stiction due improperly
released moving anchors

18. Design A: Locking mechanism
Small
displacements
 Lock open
Large
displacements
Stiffer spring
 Lateral collapse

19. Second development cycle
 Symmetrical design, two restoring springs
 Lateral stability
 Reduction in overall spring arm length
 Rotational stability
 Reduced or guided folds
 Too many contact pads for full operation!

20. Design B (Parallel plate lock)

21. Design B: Force versus displacement

22. Design B: low frequency oscillations

23. Second development cycle
 Improper parallel plate design
 Electrostatic force << Cantilever
 Trade-off in thickness of Si
 Rotational stability could be improved

24. Design C: (No lock mechanism)

25. Design C: Instant collapse

26. Second development cycle
 Symmetrically opposite spring very crucial
 Most vulnerable to lateral asymmetry
 Reduction in gap b/w the folds
 Adds to I term in the spring  stiffness
 Spring of shorter length could be achieved
 Multiple folds avoided for sensitive design
 Guided folds preferred as well

27. Design D: (Graded lock)

28. Design D: Improper release
Close to minimum feature size
Possibly lack of etch holes

29. Second development cycle
 Recommendations for design A applicable
 Same spring and actuator design
 Step-size in graded lock optimized
 Must follow the allowed feature size
 Etch holes for BHF to reach the point of release
 Multi-stable lock vs Feature size dilemma

30. General remarks toward next
development phase
Firstly improper device mapping (Few devices w/o lock)
Spring designs lacked rotational stability (Too large dimensions)
Spring implementation lacked lateral stability (Asymmetry)