1. Applications of Shape Memory Alloys to MEMS MAE 268 Greg Jarmer and Garrett Uyema

2. Outline of Presentation Shape Memory Alloys (SMA) Advantages of SMA’s for actuation of MEMS Devices Example of an Application: Microgripper Recommended Improvements of Microgripper Future Applications of SMA in MEMS

3. Shape Memory Alloys Principles of Shape Memory Alloys –Shape Memory Alloys (SMA) are alloys that exhibit the shape memory effect. –The shape memory effect is the process of restoring a deformed material back to an initial shape through a thermally induced crystalline transformation –The crystalline transformation occurs between a low temperature ductile martensitic phase and a high temperature high strength austenitic phase.

4. Shape Memory Alloys

5. Advantages of SMA’s in MEMS The main advantages of SMA’s for micro- actuation are: –SMA’s are capable of producing a large actuation force –SMA’s are capable of producing large displacements –SMA’s are activated through thermal heating

6. Disadvantages of SMA’s in MEMS The main disadvantages of SMA’s are: –Sensitivity of material properties in fabrication –Residual Stress’s developed in thin films –Nonlinearity of actuation force –Lower maximum frequency compared to other microactuator devices

7. Verification of Activation Force with FEA

8. Microgripper Theory of Operation 2 Main designs of microgrippers Location of TiNi thin film SMA actuation Transformation from martensite to austenite heating SMA thin film on the inside

9. Microgripper Fabrication of the Microgripper –2 identical cantilevers and a silicon spacer –Processes used: Deposit and etch Thin film sputtering Annealing Eutectic bonding

10. Recommended Improvements of Microgripper Be able to control hysteresis temperature range –Change composition of SMA Can shift hysteresis curve left or right –Alloy TiNi with another element such as Cu

11. Recommended Improvements of Microgripper Reduce residual stress in the thin film –Need to reduce thermal mismatch between NiTi and Si substrate –Add a layer of tungsten (W) Difference in the coefficients of thermal expansion is reduced

12. Recommended Improvements of Microgripper Increase the maximum frequency –Decrease the time it takes for phase transformation to occur –Increase surface area to volume ratio Heat can be dissipated faster

13. Future Applications of Microgrippers Grab tiny foreign objects for removal from the body –Facilitates access to intricate regions of the body Microassembly for MEMS devices Intravascular Therapy

14. Future Applications of SMA in MEMS MEMS and bioMEMS applications –Eliminate vibrations of read/write heads in hard disk drives –Microstents Promote flow in tubular passages Reinforce weak blood vessels –Microsurgery Cardiovascular applications Orthopedic applications

15. Future Applications of SMA in MEMS Simon filter Microstents SMA basket Microwrapper