Analysis Of High Frequency Vibrations Of Piezoelectric Bulk Acoustic Devices Driven By Lateral Electric Fields

Different from traditional thickness field excitation(TFE),Lateral field excitation(LFE)is a new type of resonator,which employs two electrodes on the same surface of the crystal plate.Compared to TFE,LFE has a number of advantages.There is no electrode on the region of maximum displacement,which results in higher Q values,better frequency stability,and reduced aging of the device.For LFE devices,the lack of the vibration analysis methods has influenced directly the determination of the optimal design parameters.In this paper,the LFE resonators operating with slow-shear mode with nonideal electrodes are investigated.The following works are finished.Based on the Mindlin plates theory,plate equations of the LFE devices are deduced.First-order equations of LFE quartz crystal plate considering energy dissipation are obtained by truncating equations and ignoring higher-order displacement and electric potential.Using the first-order plate equations of LFE,the free vibrations of crystal plates are analyzed and the dispersion relations of the electroded and unelectroded areas are obtained.Considering the coupled thickness-twist and face-shear vibrations,the frequency spectrums of the quartz crystal plates,namely the relationship between the frequencies and the ratios of the length to the thickness of the plates.Forced vibrations analysis are carried out on LFE quartz crystal plates and the relationship between the dynamic capacitances and the frequencies are obtained.Resonance modes with good energy trapping characteristics are achieved by analyzing the coupled thickness-twist and face-shear vibrations.Finally,the influences of the parameters of the devices on the vibration characteristics are analyzed,such as the electrode gap,the size of the electrode and the electrode/plate mass ratio R.LFE devices are designed and fabricated.Theoretical results are verified by testing the impedance characteristics of the devices.The research results can provide theoretical bases for the design of LFE piezoelectric bulk acoustic wave devices,and have positive promoting effect on the developing of high-performance LFE resonators and sensors.