Study On FeGaB Thin Film Properties And Its Application In SAW Devices

Modern industry has an increasing demand for high-performance and high-precision magnetic materials.As an important part of magnetic materials,magnetostrictive films are widely used in information storage,magnetic sensing,power conversion and other fields.FeGaB,as a new type of magnetostrictive thin film,has the characteristics of high stability,high magnetostriction coefficient and easy preparation,which has become a research hotspot in the field of magnetostriction.However,there is a big gap in the preparation process of FeGaB film in domestic compared with foreign,which limits the development of related research in domestic.In this thesis,the FeGaB single-layer film with excellent soft magnetic properties was successfully prepared by optimizing the preparation process conditions.In order to make the film can be applied in the high frequency field,the FeGaB/Al₂O₃ multilayer thin film with high electrical resistivity and excellent soft magnetic properties was prepared,and the application of FeGaB film in surface acoustic wave（SAW）devices was further studied.A magnetic field sensor based on SAW is prepared,which provides a new idea for realizing a new type of high-precision magnetic field detection.First,FeGaB thin films were prepared by target co-sputtering technique.The optimal preparation conditions of single-layer FeGaB thin films were studied,including the sputtering power of Fe Ga and B,sputtering pressure,sputtering substrate temperature and the size of the applied magnetic field.By altering the process conditions,a range of FeGaB films with varying soft magnetic properties were synthesized.The hysteresis curve measurement and magnetostriction coefficient test of these films were conducted.It was found that when the sputtering power of Fe Ga was 40 W,the sputtering power of B was 70 W,the sputtering pressure was 1.6 Pa,the sputtering substrate temperature was 75℃,and the applied horizontal magnetic field was 120 Oe,the prepared FeGaB films exhibited the best soft magnetic properties,with a coercive force of 1.7 Oe and a magnetostriction coefficient of 66 ppm,which was a notable improvement compared to the known FeGaB films in domestic.In order to address the significant eddy current loss of single-layer FeGaB films in high frequency applications,an Al₂O₃ insulating layer was incorporated into the FeGaB film to enhance its electrical resistivity and reduce eddy current loss.The effects of the number of layers,annealing temperature,and annealing time on the properties of FeGaB/Al₂O₃ multilayer thin films were further investigated.Multilayer thin films with varying layers were prepared and their properties were analyzed.After conducting a comprehensive analysis,the[FeGaB（63 nm）/Al₂O₃（5 nm）]×8 multilayer thin film was selected as the research object.The coercive force of the multilayer thin film was 11.2 Oe,the magnetostriction coefficient was 59 ppm,and the electrical resistivity was improved by two orders of magnitude in comparison to that of the single-layer FeGaB film.The multilayer thin film was then annealed at various temperatures and times,and its coercive force,magnetostriction coefficient,and other performance indicators were analyzed.Finally,the optimal annealing parameters were determined to be annealing at 100℃for 10 minutes.Under this annealing condition,the coercive force of the multilayer thin film was 6.8 Oe,the magnetostriction coefficient was 63 ppm,and the magnetic properties were significantly enhanced.Finally,an innovative FeGaB/Al₂O₃ multilayer thin film was prepared in the middle of the SAW device as a magnetic field sensor,and the process flow of the sensor was studied,including pretreatment,homogenization,exposure,development,magnetron sputtering,and stripping.The FeGaB/Al₂O₃ multilayer thin film with a width of 600μm was engraved in the center of the SAW device.The sensitivity of the prepared sensor to magnetic fields was assessed using a network analyzer.The experimental results demonstrate that the device has a sensitivity of approximately 0.3,2.4,0.81,and 0.09 degrees per minute in the range of 0-20 Oe,20-25 Oe,25-90 Oe,and 95-150 Oe,respectively,exhibiting phase change with magnetic field and good linearity.Subsequent experiments were conducted to evaluate the stability of the sensor,which revealed that it had superior stability and potential for application.This thesis provides a useful reference and guidance for the optimal preparation of magnetic materials and the advancement of magnetic field sensing technology.Future research should consider the utilization of other processes to further enhance the performance of FeGaB films and FeGaB/Al₂O₃ multilayer thin films,and explore potential application scenarios of FeGaB films to make greater contributions to the advancement of magnetic films.