Experimental study and numerical analysis of aging of piezoelectric resonators.

摘要

Aging of piezoelectric (quartz crystal) resonator has been identified as one of the most important quality control problems of quartz crystal products. Aging is defined as frequency change with time. Aging in quartz resonators can be due to several sources such as mass transfer due to contamination inside the resonator enclosure, stress-strain in the resonator blank, quartz defect, etc. In this study, the stress-strain effect, which has been believed so many years as a dominant factor contributing to aging, was studied. These effects are caused mainly by the long-term properties of bonding adhesive that attach quartz crystal plate to the ceramic base package in addition to the thermal mismatch between quartz crystal and adhesive. With the available accelerating testing method such as temperature-controlled chamber, the stress-strain induced aging in the quartz crystal resonators can be investigated. Because of the miniaturized size of the resonator, a digital image analysis method called Image Intensity Matching Technique was applied to obtain deformation patterns in the quartz blank due to thermal load. Our preliminary results have shown that the un-symmetric plane deformations may be a dominant contributing factor to aging induced frequency shift. For simulation purposes, finite element analysis was used to investigate the deformation patterns (i.e., stress-strain distributions) and corresponding natural frequency shift in the piezoelectric resonators. The viscoelastic behavior of mounting adhesives were incorporated into analysis to show the dominant effect of long term behavior of stress-strain developed in the crystal resonators. For this purpose, creep test was conducted to obtain viscoelastic parameter of conductive adhesive. Some geometrical aspects, such as uneven mounting supports due to distances, volumes and heights of the adhesives were simulated in the model. Also, contamination effect due to mass loading in the electrode's region was studied to investigate which regions have significant contribution to aging.