Study On The Preparation And Characteristics Of ZnO Piezoelectric Thin Films And Related Surface Acoustic Wave Devices

SAW?Surface acoustic wave?device has been successfully used in many areas,such as radio and television,mobile communications,radar,navigation,electronic warfare,remote telemetry systems and so on,due to the characteristics of high operating frequency,large bandwidth,small size,good repeatability and stablility.ZnO has the advantages of piezoelectricity,transparent conductivity,gas sensitivity and ultraviolet light emission.Moreover,the ZnO piezoelectric thin films have large electro-mechanical coupling coefficient and small insertion loss,so the SAW device based on ZnO piezoelectric thin films has been obtained much more attention.In this paper,the preparation and characteristics of ZnO piezoelectric thin films and their acoustic surface devices are studied,the main contents are as follows:1)ZnO thin films are deposited by RF?Radio Frequency?magnetron sputtering on SiO₂substrate.And the SAW delay lines based on?002?ZnO/IDT/SiO₂ structures are fabricated,by which the Rayleigh waves are excited.The propagation characteristics of Rayleigh waves,such as frequency response,phase velocity?v_p?,electro-mechanical coupling coefficient?k²?,are characterized experimentally.Meanwhile,the properties of Rayleigh waves are theoretically investigated by 3D finite element method?FEM?.The experimental and theoretical results are in good agreement with each other.Furthermore,the effects of IDT position and ZnO crystal orientation on the characteristics of SAWs are also theoretically studied by COMSOL.The results indicate that Rayleigh wave excited by?002?ZnO/IDT/SiO₂ structure has the maximum k² of 3.63%at h_z/?=0.46;Love wave excited by IDT/?110?ZnO/SiO₂ structure has the maximum k² of 5.82%at h_z/?=0.31.2)SiO₂ thin films and ZnO thin films are deposited on Si substrates by RF magnetron sputtering method.The SAW delay lines based on?002?ZnO/IDT/SiO₂/Si structure are fabricated,and the acoustic properties of SAWs are analyzed experimentally and theoretically.In addition,the effect of IDT position and ZnO crystal orientation on the characteristics of SAWs are also investigated,the results show that Rayleigh wave in the structure of?002?ZnO/IDT/SiO₂/Si has the maximum k² of 3.85%with h_z=8?m and h_s/?=0.15;and Love wave in the structure of IDT/?110?ZnO/SiO₂/Si has the maximum k² of 6.31%with h_z=5?m and h_s/?=0.06.3)The FEM models of SAW delay lines based on the structure of SiO₂/?002?ZnO/IDT/SiO₂/Si,SiO₂/?110?ZnO/IDT/SiO₂/Si and SiO₂/IDT/?110?ZnO/SiO₂/Si are established by COMSOL,which are used to investigate the influence of SiO₂ waveguide layer on the characteristics of excited SAWs.The results indicate that the k² of Rayleigh wave excited by the structure of?002?ZnO/IDT/SiO₂/Si and?110?ZnO/IDT/SiO₂/Si are increased by the top layer of SiO₂.And the k² of Rayleigh wave excited by the structure of SiO₂/?002?ZnO/IDT/SiO₂/Si and SiO₂/?110?ZnO/IDT/SiO₂/Si are firstly increased and then stable with the bottom layer increasing.