micromirrors for biomedical imaging and display systems actuated by curved multimorphs
Video: A 1mm wide circular mirror actuated by a semicircular multimorph.
Motivation:
- The combined bending and twisting deformation of curved multimorphs can be utilized to achieve low mirror center shift during scanning.
Figure 1: (a) Schematic with straight bimorph shows shift in mirror plate center during actuation (b) Schematic of a 50 μm wide mirror plate with a Al-SiO2 semicircular actuator (R= 35 μm, w=10 μm) (c) FE Simulation shows that the mirror-plate tilts by 13.5° for -200 K temperature change. The mirror-plate center shifts by 0.4 μm only.
- Twisting deformation of curved multimorphs implies a high resonant frequency. Micromirrors actuated by curved piezoelectric multimorphs can be used for display systems.
- Since a high resonant frequency may be achieved using a single curved multimorph, power consumption is much less than comparable designs actuated by straight multimorphs.
- Two dimensional scanning can be achieved using a single curved multimorph.
Figure 2: Scanning resonant modes of an elliptical micromirror with 50 μm semi-minor axis and 100 μm semi-major axis. The 5 μm wide elliptical bimorph beam consists of 1 μm thick Al and 0.4 microns thick W layers. (a) Scanning about x-axis (2.5 kHz). (b) Scanning about y-axis (4.4 kHz).
Approach:
- Micromirrors actuated by circular and elliptical curved multimorphs were fabricated on SOI wafer.
Figure 3: SEMs of mirrors actuated by curved Al-W multimorphs (a)Elliptical mirror with 140 μm major axis, 90 μm minor axis (b) Elliptical mirror with 190 μm major axis, 90 μm minor axis (c)1mm wide circular mirror (d) 400 μm wide circular mirror
- The multimorph layers are Al-SiO2-W-SiO2. SiO2 encapsulates the W layer and electrically isolates it from the Al layer. Actuation can mainly be attributed to difference in thermal expansion coefficients between the Al and W layers.
- W acts as a resistive heater and as an active layer of the multimorph.
Results:
Figure 4: Static characteristic of mirror shown in Fig. 3(c)
Figure 5: Frequency response of mirror shown in Fig. 3(c)
Figure 6: Two-dimensional scan pattern generated by the mirror shown in Fig. 3(c)
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.