The Magnetic Surface Acoustic Wave Magnetic Field Sensor And Its Preparation Method

Magnetic filed detection is very important to our daily life, industry and nationaldefense. In the thesis, magnetic surface acoustic wave sensor (MSAW) has beenstudied and fabricated in order to overcome the intrinsic difficulties in the emergingmagnetic field sensor based magnetoelectric effect. The MSAW consists of apiezoelectric ZnO thin film, a magnetostrictive FeSiBC thin film and the interdigitalelectrodes. The ZnO thin film has the advantage of excellent c-axis oriented, highresistivity and low roughness. The magnetostrictive FeSiBC thin film with uniaxialanisotropy has the giant Young’s modulus effect. Therefore, all of these allow us toachieve the goal of miniaturized, integrated, broadband magnetic field sensor with veryhigh sensitivity. The main work of this thesis includes1) ZnO thin films were deposited on the Pt/Ti/SiO2/Si substrate by RF magnetronsputtering. The influence of sputtering pressure, the ratio of argon to oxygen, substratetemperature, sputtering power and annealing conditions on the properties of ZnO thinfilm were investigated in details, i.e. microstructure, electrical resistivity and surfacemorphology. The optimized sputtering parameters were determined as follows:pressure0.9Pa, the Ar/O2ratio2:1, deposition temperature450°C, sputtering power100w and annealing in O2at800°C for one hour. The full width at half maximum(FWHM) of ZnO (002) peak of4.185deg, high resistivity greater than109·cm andsurface roughness less than10nm are gained, which satisfies the requirements of theSAW devices.2) DC magnetron sputtering deposition was used for coating FeSiBC thin film onthe glass. The sputtering pressure and power were varied in order to obtain the bestproperty of the FeSiBC thin film. The magnetic hysteresis loop, phase structure andmagnetostrictive coefficient are presented in the thesis. In order to fulfill therequirement of MSAW on the magnetostrictive film thickness, I have also prepared(FeSiBC/Cu/FeSiBC) sandwiched structure and annealed the films in magnetic filed atdifferent temperature. The first technique clearly has positive effects on the property ofthe FeSiBC thin film, however the later showed litter influence. 3) Based on the theoretic analysis of structure parameters, a SAW resonator(SAWR) was fabricated using the lift-off method. The wavelength is8μm and thecenter frequency is343MHz and. COMSOL Multiphysics was used to simulate theSAWR. The center frequency, deformation, admittance and quality factor wereanalyzed. The influence of aperture was also modeled.4) Finally, ZnO layer and FeSiBC layer were integrated by adopting the sacrificialprocessing technology. The whole process to manufacture the MSAW sensor ispresented.