The spurious vibration analysis of ceramic resonator using 3rd overtone vibration

Various vibration modes used in ceramic resonators which have been commercialized recently, and they have been mainly used in generating frequencies greater than 10 MHz with the 3^rd overtone vibration (TE3 mode vibration) and 2^nd vibration (TE2 mode vibration) generated by laminating two layers. In the case of the TE2 mode vibration, it is known there is no problem of a spurious response generated in the TE3 mode vibration. In this study, the TE3 mode vibration and TE2 mode vibration of PbTiO₃-based ceramics were simulated by the FEMLAB program and compared the results, which simulation revealed that the TE2 mode generated vibration in a more local area than TE3 mode. We tried to investigate the origin of the spurious response in TE3 mode vibration by analyzing the influences of the ratio of electrode overlap length (L) per thickness (T) of resonators. It was found that the anti-resonant frequency of a TE3 vibration and the resonant frequency of a spurious vibration became closer to split impedance shape with increasing the electrode overlap length, and the resonant impedance of TE3 vibration became unstable in short overlap length. It was expected that the TE3 mode would be less influenced by spurious vibrations in a L/T ratio of 2.0 ~3.0 in a manufactured resonator.