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analysis and fabricatiON of curved multimorph actuators

Motivation:

• Straight bimorphs [1] and multimorphs [2] are well understood and have been widely used for achieving out-of-plane bending in thermal and piezoelectric MEMS devices.
  
• Unlike straight bimorphs that only undergo bending, curved bimorphs bend and twist during deformation.
  
• Analysis of curved bimorphs will greatly increase the design space available to MEMS engineers.

Figure 1: Bimorph actuator (a) Undeformed (b) deformed. The out-of-plane displacement and twist-angle and z and φ respectively.

Objectives:

• Analysis of curved bimorphs and multimorphs for small deformation
• Fabrication of curved multimorphs
• Validation of analysis using experiments and simulations
• Application of curved multimorphs
  

Approach:

• The three components of curved multimorph analysis are
• Strain produced in the thin-film layers by thermal/piezoelectric effects [2]
  
• Deformation equations for curved beams [3]
  
• Strain continuity at the interface between thin-films

• Curved bimorphs and multimorphs with in-plane radius of curvature in the range 25 -500 microns were fabricated. A laser beam reflected from a rigid mirror plate attached to the multimorph was used to track its deformation at different ambient temperatures.

Figure 2: Fabricated curved multimorph structures.

 Results:

 Figure 3: (a) Tip-deflection (b) Beam-twist of a 50 microns long, 6 microns wide, singly-clamped multimorph with the following layers — 0.15 microns SiO₂ - 0.6 microns W - 0.2 microns SiO₂ - 0.7 microns Al — for a temperature change of 100 K.

Figure 4: Experimental, analytical and simulation results for structure shown in Fig. 2. Discrepancies at large deformation may be attributed to the small-deformation assumptions used during analysis.

Qualitative study for large deformations:

Publications:

• S. Pal, H. Xie, "Analysis simulation and fabrication of curved multimorph microactuators ," submitted to Transducers 2011, Beijing, June 5-9, 2011.
• S. Pal, H. Xie, “Analysis and Simulation of Curved Bimorph Microactuators," Microtech Conference and Expo, Anaheim, CA, USA, June 21-24, 2010.
  

Patents Pending:

• S. Pal, H. Xie and K. Zawoy "MEMS Designs Based on Curved Multimorph Microactuators that Generate Combined Bending and Twisting", invention disclosure #UF13407.