| In recent years,due to the advantages of high speed and low power consumption of magnon devices,the research on the propagation characteristics of spin waves?SW?have received extensive attention in the academic community.The band gap frequency and depth of the magnon crystal can be modulated by changing the frequency and intensity of the surface acoustic wave?SAW?,so that SAW can be introduced to study the propagation characteristics of the SW.However,research on the high frequency propagation characteristics of spin waves based on surface acoustic waves will be the trend of future development.In order to study the high frequency characteristics of SW,it is very important to excite high frequency SAW.However,the key to exciting high frequency SAW is to fabricate high quality piezoelectric materials.ZnO thin film is an ideal piezoelectric material with high electromechanical coupling coefficient and low dielectric constant.Based on the above background,this paper proposed to prepare high quality ZnO thin films on yttrium iron garnet?YIG?for exciting high frequency SAW.In view of the relatively expensive YIG substrate,the yttrium gallium garnet?GGG?substrates with the same garnet structure and similar properties as YIG were used to investigate the preparation process of ZnO thin films,thereby reducing the experimental cost.The main works of this thesis are as follows:ZnO thin films were deposited on Si substrates by radio frequency magnetron sputtering.The effects of sputtering power,oxygen flow rate and annealing temperature on ZnO thin films were investigated.The experimental operation flow of the whole process of preparing ZnO thin films was familiarized.The preparation for exploring the preparation of ZnO thin films on GGG substrates was made.The optimum process parameters for preparing ZnO thin films on Si substrates were obtained as follows:the base vacuum pressure is 1.5×10-4 Pa,the sputtering pressure is 0.88 Pa?80sccm?,the sputtering power is 80W,the oxygen flow rate 6 sccm,the distance between the target and the substrate is 7.8 cm,annealing for 1 h in oxygen atmosphere,and annealing temperature 400?,the average growth rate of the films is 0.1292 nm/s.Finally,ZnO films with high c-axis orientation,low residual stress and uniform smoothness were obtained on the Si substrates.ZnO thin films were deposited on GGG substrates by radio frequency magnetron sputtering.The effects of sputtering power,oxygen flow rate and annealing temperature on ZnO thin films were investigated.The optimum process parameters for preparing ZnO thin films on GGG substrates were obtained as follows:the base vacuum pressure is 1.5×10-4 Pa,the sputtering pressure is 0.88 Pa?80sccm?,the sputtering power is 80W,the oxygen flow rate 4 sccm,the distance between the target and the substrate is 7.8 cm,annealing for 1 h in oxygen atmosphere,and annealing temperature 450?,the average growth rate of the films is 0.173 nm/s.Finally,the high c-axis preferred orientation growth,low residual stress,and uniform smooth ZnO thin films were obtained on the GGG substrate.In order to fabricate SAW resonator,the fabrication process of interdigital transducer was explored.The lithography interdigital transducer was fabricated on ZnO/Si and ZnO/GGG,and the interdigital width of the transducers was 4 microns.Due to the difference of substrate structure,the pre-exposure time of the two structure lithography processes is obviously different.The pre-exposure time of the ZnO/Si structure is 6.2s,and that of the ZnO/GGG structure is 3.5s.The metal aluminum film was plated by magnetron sputtering,stripping of electrodes in AZ400T degumming solution at 70?to complete the preparation of the SAW single-port resonator.The SAW single-port resonator was tested by using a vector network analyzer.The center frequency of the ZnO/Si structure single-port resonator is 298 MHz,the corresponding phase velocity is4768 m/s,and the electromechanical coupling coefficient is 3.92%.The center frequency of the ZnO/GGG structure single-port resonator is 201MHz,the corresponding phase velocity is 3216m/s,and the electromechanical coupling coefficient is 0.22%.It is proved that the prepared ZnO thin films have the potential for high frequency SAW modulation SW excitation and propagation characteristics. |
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