A study on raising the fundamental TS-mode resistance by energy trapping for 3rd overtone resonator performance enhancement

AT-cut quartz resonator is used widely as a frequency source in electric devices. The main mode of AT-cut quartz plate is thickness-shear mode, which the frequency is inverse proportion to the plate thickness. Due to the sandwich structure, only odd thickness-shear overtones exist in AT crystal resonators. Normally, the vibration amplitude of fundamental mode is larger than that of all overtones. And that means the effect-series-resistance of the fundamental mode is lowest. In this paper, different energy trapping effects of fundamental and 3rd overtone are used to control the resistance ratio of these two modes. Two kinds of 5.0*3.2mm size resonators, 50MHz and 54MHz 3rd overtone (the fundamental mode frequencies are 16.67MHz and 18MHz, respectively), with different beveled chips are made. Comparing to the 3rd overtone, the fundamental mode has longer wavelength and stronger penetration ability to sink energy through the mounted end. The experiment data show that a proper beveling could cut the energy flux of 3rd overtone off, but allow some energy flux of fundamental mode propagates outward. And then the resistance ratio of these two modes could be controlled.