Fabrication of piezoelectric AlN thin film for FBARs |
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Authors: | Wei-Kuo Liu Kok-Wan Tay Sin-Cha Kuo and Menq-Jion Wu |
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Institution: | (1) Department of Mechatronics Engineering, National Changhua University of Education, Changhua, 500, Taiwan, China;(2) Department of Electrical Engineering, Wu Feng Institute of Technology, Chiayi, 62153, Taiwan, China;(3) Department of Electronics Engineering, Far East University, Tainan, 744, Taiwan, China |
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Abstract: | This paper focuses on the fabrication of film bulk acoustic-wave resonator (FBAR) comprising an aluminum nitride (AlN) piezoelectric
thin film sandwiched between two metal electrodes and located on a silicon substrate with a low-stress silicon nitride (Si3N4) support membrane for high frequency wireless applications, and analyzes the optimization of the thin AlN film deposition
parameters on Mo electrodes using the reactive RF magnetron sputter system. Several critical parameters of the sputtering
process such as RF power and Ar/N2 flow rate ratio were studied to clarify their effects on different electrodes characteristics of the AlN films. The experiment
indicated that the process for Mo electrode was easier compared with that of the Pt/Ti or Au/Cr bi-layer electrode as it entailed
only one photo resist and metal deposition step. Besides, Pt/Ti or Au/Cr electrodes reduced the resonance frequency due to
their high mass density and low bulk acoustic velocity. Compared with the case of the Al bottom electrode, there is no evident
amorphous layer between the Mo bottom electrode and the deposited AlN film. The characteristics of the FBAR devices depend
not only upon the thickness and quality of the AlN film, but also upon the thickness of the top electrode and the materials
used. The results indicate that decreasing the thickness of either the AlN film or the top electrode increases the resonance
frequency. This suggests the potential of tuning the performance of the FBAR device by carefully controlling AlN film thickness.
Besides, increasing either the thickness of the AlN film or higher RF power has improved a stronger c-axis orientation and tended to promote a narrower rocking curve full-width at half-maximum (FWHM), but increased both the
grain size and the surface roughness. An FBAR device fabricated under optimal AlN deposition parameters has demonstrated the
effective electromechanical coupling coefficient (k
eff2) and the quality factor (Q
f
x
) are about 1.5% and 332, respectively. |
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Keywords: | sputtering thin film piezoelectric |
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