Research Of Ultraviolet Detector Based Surface Acoustic Wave

Most of the energy of surface acoustic wave is limited to the near surface area,resulting in its high sensitivity to any slight disturbance on the surface of piezoelectric materials,suitable for a variety of physical and chemical signal sensing.It is of great significance to study the high sensitivity UV detector based on surface acoustic wave technology.In this paper,zinc oxide(ZnO)piezoelectric thin films are deposited on silicon wafers by rf magnetron sputtering.Based on this,a single-port SAW resonator with the characteristic size of 8?m,100 pairs of cross finger electrodes and 80?aperture has been designed.COMSOL software was used for the finite element simulation analysis of the above devices.The simulation results show that the center frequency of the device is140.29 MHz,and the surface acoustic wave velocity is 4489.76 m/s.The device was fabricated by photolithography and stripping process,and the test result of the real device was 136 MHz,which was close to the simulation result.The device can achieve a frequency offset of 102.60 k Hz and a sensitivity of 0.80 ppm/(?W/cm~2)under ultraviolet irradiation of 900?W/cm~2 at 365nm wavelength.In order to improve the performance of ZnO thin film surface acoustic wave devices,the effects of Li Nb O₃,sapphire and PZT substrates on the performance of ZnO thin film and SAW devices were investigated.The test results show that the center frequency of Li Nb O₃/ZnO based device is 126.54 MHz,and the surface acoustic wave velocity is4049.28 m/s,and the center frequency of Si/PZT/ZnO based device is 127 MHz,and the surface acoustic wave velocity is 4064 m/s.The actual test results are basically consistent with the simulation results.Among them,Li Nb O₃ substrate can improve the photoresponse performance of the detector.Li Nb O₃/ZnO device can achieve 127.5 k Hz frequency offset and 1.43 ppm/(?W/cm~2)sensitivity under the irradiation of 365nm wavelength light.In order to further optimize the piezoelectric properties of ZnO thin films and the optical response of devices,ZnO thin films were doped with 0.5at%Bi,5at%Mg and2at%Mn,respectively,to study the effect of doping on the structure and device performance of ZnO thin films.X-ray diffraction(XRD)and atomic force microscopy(AFM)were used to characterize the microstructure of ZnO doped films.The results show that the(002)diffraction peak of 0.5 at%Bi doped ZnO films has a minimum half-width of 0.269°,and the grain distribution uniformity is good.The photoresponse performance of the uv detector based on 0.5at%Bi doped ZnO film is improved obviously.The center frequency shift is 290 k Hz and the sensitivity is 3.47 ppm/(?W/cm~2)at 365nm wavelength and the optical power density is 900?W/cm~2.