Vibration mode observation of piezoelectric disk‐type resonator by high‐frequency laser Doppler vibrometer

For future mobile phones based on cognitive radio technology, a compact multiband RF front‐end architecture is strongly required, and an integrated multiband RF filter bank is a key component in it. Contour‐mode resonators are receiving increased attention for a multiband filter solution, because their resonance frequency is mainly determined by their size and shape, which are defined by lithography. However, spurious responses, including flexural vibration, are also excited due to the thin structure of the devices. To improve resonator performance and suppress spurious modes, visual observation with a laser probe system is very effective. In this paper, we prototyped a mechanically coupled disk‐array filter, which consists of a silicon disk and two disk‐type resonators of higher‐order wineglass mode, and observed its vibration modes using a high‐frequency laser Doppler vibrometer (UHF‐120, Polytec, Inc.). It was confirmed that the higher‐order wineglass mode vibration included a compound displacement, and that its out‐of‐plane vibration amplitude was much smaller than that of other flexural spurious modes. The observed vibration modes were compared with FEM (Finite Element Method) simulation results. In addition, it was also confirmed that fabrication error (e.g., misalignment) induced asymmetric vibration. © 2012 Wiley Periodicals, Inc. Electron Comm Jpn, 95(5): 33–41, 2012; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/ecj.10406