12 May 1995 Silicon micromachined piezoelectric ZnO bimorphs as micromirrors for display applications
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Abstract
Cantilever beams of piezoelectric heterogeneous bimorphs (ZnO-on-Si3N4 bimorphs) have been designed and fabricated on silicon wafers for applications as micro-mirrors. The bimorph is a composite beam comprised of a bottom layer of Si3N4 and a top layer of ZnO which has been metallized with Au/Cr film on both surfaces. A metallized rectangular pad near the tip of the bimorph has been designed to serve as a deflecting micro-mirror. The fabrication procedures of the bimorphs using surface-machining method with ZnO as the sacrificial layers are presented in the paper. Measurement of the deflection of the bimorph as a function of dc voltages showed two different regimes of voltage dependence. For voltage magnitude less than 1 volt, small and linear deflection was obtained which was consistent with the theoretical prediction. At voltage magnitude larger than 1 volt, large deflection was obtained with quadratic dependence on the magnitude of the applied voltage. The large deflection can be attributed to joule heating effect due to current conduction in the semiconducting ZnO. The fundamental resonance frequency of the bimorph has been measured and is in close agreement with the predicted value obtained from the Euler-Bernoulli beam equation. Because of the quadratic dependence on the voltage, resonance can be obtained even though the frequency of the driving signal was only at half of the true resonance frequency. Air damping was observed which led to a reduction of the Q-factor. To test the bimorph for micro-mirror display applications, a HE-Ne laser beam has been directed at a metallized pad at the tip of the bimorph. A sinusoidal signal superimposed with a dc bias has been applied to the bimorph. The scanning range of the reflected laser beam is reported and discussed in the presentation.
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Johannes G. Smits, Wai-Shing Choi, M. Edward Motamedi, Angus P. Andrews, "Silicon micromachined piezoelectric ZnO bimorphs as micromirrors for display applications", Proc. SPIE 2383, Micro-Optics/Micromechanics and Laser Scanning and Shaping, (12 May 1995); doi: 10.1117/12.209045; https://doi.org/10.1117/12.209045
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