RF sputtered piezoelectric zinc oxide thin film for transducer applications |
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Authors: | Yu-Hsiang Hsu John Lin William C Tang |
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Affiliation: | (1) Department of Biomedical Engineering, University of California, 3120 Natural Sciences II, Zot 2715, Irvine, CA 92697-2715, USA;(2) Department of Electrical Engineering and Computer Science, University of California, Irvine, CA, USA |
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Abstract: | This paper demonstrates the substrate dependency of the c-axis zinc oxide growth in radio-frequency sputtering system. Different deposition conditions were designed to study the influences
of Si, SiO2/Si, Au/Ti/Si, and Au/Ti/SiO2/Si substrates on the piezoelectric and crystalline qualities of the ZnO thin films. Experimental results showed that the
multilayer of Au/Ti/SiO2/Si-coated silicon substrate provided a surface that facilitated the growth of ZnO thin film with the most preferred crystalline
orientation. The 1.5 μm-thick thermally grown amorphous silicon dioxide layer effectively masked the crystalline surface of
the silicon substrate, thus allowing the depositions of high-quality 20 nm-thick titanium adhesion layer followed by 150 nm-thick
of gold thin film. The gold-coated surface allowed deposition of highly columnar ZnO polycrystalline structures. It was also
demonstrated that by lowering the deposition rate at the start of sputtering by lowering RF power to less than one-third of
the targeted RF power, a fine ZnO seed layer could be created for subsequent higher-rate deposition. This two-step deposition
method resulted in substantially enhanced ZnO film quality compared to single-step approach. The influence of stress relaxation
by annealing was also investigated and was found to be effective in releasing most of the residual stress in this layered
structure. |
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