Research On Resonator Based On Lithium Niobate And Lithium Tantalate Single Crystal Piezoelectric Thin Film

Under the fifth-generation mobile communication technology standard,the current radio frequency front-end filter faces two difficulties: frequency increase and bandwidth expansion.The piezoelectric resonator,as the basic unit of the impedance element filter,its performance indicators play a decisive role in the performance of the filter.In recent years,single crystal piezoelectric thin-film resonators based on ion slicing technology,have shown excellent performance in frequency increase and bandwidth expansion.The thesis researches the piezoelectric resonators based on two single crystal thin-film materials,lithium niobate and lithium tantalate.Detailed works are as follow:(1)By performing coordinate transformation on piezoelectric parameters,the material electromechanical coupling coefficients of rotating Y-cut lithium niobate and lithium tantalate are calculated,among them,the form of electric field excitation is single-sided interdigital electrodes and upper and lower electrodes.Then the work analyzes the performance advantages of 128?Y-cut lithium niobate and 42?Y-cut lithium tantalate.(2)This work researches the frequency response characteristics of the first-order antisymmetric lamb wave resonator based on 128?Y-cut lithium niobate.By establishing a two-dimensional resonant cavity model and theoretical derivation,the relationship between the resonance frequency and the ratio of the thickness of the piezoelectric film to the electrode period is obtained.Through finite element simulation,the relationship between the electromechanical coupling coefficient and the ratio of the thickness of the piezoelectric film to the electrode period is obtained.The influence of electrode parameters on the frequency response of the resonator is studied: using aluminum electrode and increasing the spacing between electrodes,the frequency response characteristic curve is smoother,adjusting the number of electrode pairs can meet the 50 ohm impedance matching requirement,and adjusting the electrode thickness parameter can improve the quality factor.Using ladder filter topology,series and parallel resonator meeting the filter parameters of n79 frequency band is designed.(3)Solidly mounted type and cavity type resonators based on 42?Y-cut lithium tantalate are studied.In solidly mounted type resonator,through finite element simulation and experimental verification,this work draws the following conclusions:increasing the number of electrode pairs can significantly improve the performance coefficient of the resonator;at the same time,the increase in the number of electrode pairs will also lead to the enhancement of the parasitic mode,using dummy-electrode structure can effectively suppress its response.Through finite element simulation,the electromechanical coupling coefficient of the resonator increases first and then decreases with the increase of the electrode period,and it has a theoretical maximum of 10.8% at the electrode period width of 1.8?m under the substrate parameters used in this experiment.In this work,a cavity type resonator was fabricated using deep silicon etching and electron beam exposure process.Actual tests and finite element simulations showed that there are many parasitic modes.