Research Of Magnetoelectric Saw Resonator With Negative Poisson's Ratio Magnetostrictive Structure

In recent years,people have devoted themselves to the combination of layered magnetoelectric materials and surface acoustic wave technology to realize magnetic field detection.It is of great academic significance and application value to study magneto-acoustic surface waves in the field of magnetic sensing.In this thesis,an integrated magnetoacoustic surface wave resonator based on ScAlN/FeGa multilayer structure is proposed,which can be used for high sensitivity detection of DC and broadband magnetic fields.The main work of this thesis is as follows:Firstly,from the elastic modulus in any direction of anisotropic media,the three-dimensional anisotropy image of Young's modulus of FeGa crystal is obtained,and the stress and magnetic negative Poisson's ratio effect and mechanism are combed.Then the elastic wave in the anisotropic medium is calculated to obtain the in-plane and diagonal slowness curves of different FeGa alloys.The effect of negative Poisson's ratio on the slowness curve is discussed.Secondly,numerical analysis and finite element simulation software are used to calculate the dispersion curve,electromechanical coupling coefficient and cutoff frequency of Rayleigh wave propagation in different directions in the semi-infinite heterostructure of ScAlN/FeGa.The calculation results show that when the Rayleigh wave propagates in the direction of Fe_81.3Ga_18.7?001?[100],the cutoff value of the resonance frequency and the thickness of the piezoelectric film fh is only 0.3 GHz·?m,and the phase velocity v_p varies from 2175 to 2250 m/s,the electromechanical coupling coefficient K² varies from 0 to 0.4%;When the Fe_81.3Ga_18.7?001?[110]direction with negative Poisson's ratio is propagated,the cutoff value of fh is increased to 1.58GHz·?m,the v_p range is 3000?3300 m/s,and the range of K² is 0.2?1.2%.The vibration mode and admittance characteristics of the above-mentioned different directions are simulated by COMSOL,and the important influence of the FeGa negative Poisson's ratio effect on the Rayleigh wave propagation characteristics is obtained.Next,the highly c-axis oriented ScAlN film was prepared by RF magnetron sputtering on a FeGa alloy substrate.The half-height width of the rocking curve was only3.68°,the thickness was 1.2?2?m,the surface roughness was 5nm,and the film-based adhesion was 22N.All performance indicators are in line with the preparation requirements of SAW resonators.Finally,an interdigital transducer was fabricated on the ScAlN/FeGa structure by lift-off process with line width and wavelength of 4?m and 16?m,respectively.Single-port magnetoelectric SAW resonators were tested using a vector network analyzer and a microwave probe station.The test results show that the resonant frequency f_r of the Sc_21.3Al_78.7N/Fe_81.3Ga_18.7 structure SAW resonator is 176MHz,and the electromechanical coupling coefficient K² is 0.7%.A variety of modes appear in the Sc_21.3Al_78.7N/Fe_72.8Ga_27.2structure SAW resonator,where the Rayleigh wave has a f_r of 259 MHz and a K² of 1%.The sensitivity analysis of the magnetic field of the resonator shows that when the frequency resolution is 100 Hz,the magnetic field sensitivity of the resonator can reach 4.2×10^-9 Tesla,which can realize high sensitive magnetic field detection.