Preparation And Research Of High Frequency SAW Devices Based On AlN/ZnO Multilayer Structure

In the 5G information age,with the rapid development of communication technology,the demand for high frequency surface acoustic wave(SAW)devices has increased sharply.Reducing the insertion loss on the basis of improving the frequency characteristics of SAW devices is a research hotspot at present.In view of the contradiction between low loss and high frequency of SAW devices,this thesis mainly explores the optimization of piezoelectric composite structure and SAW device structure,which has certain scientific significance and application value for the low loss characteristics of high frequency SAW devices urgently needed in the 5G information age.In this thesis,the effects of annealing temperature on the properties of ZnO thin films,sputtering power and ZnO buffer layer thickness on the properties of AlN thin films on silicon-based substrates were systematically studied.Through the test analysis of XRD,AFM and PFM characterization methods,the optimum process conditions were obtained: when the annealing temperature of ZnO thin film was 650?;the sputtering power of AlN thin film was 220 W;and the thickness of ZnO buffer layer was 60 nm,the AlN thin film had the best(002)orientation,minimum FWHM value and maximum total piezoelectric amplitude(144 pm),and the optimal AlN/ZnO composite structure was prepared.Then,SAW resonators with different IDT structures(with or without center grating at 100 nm interdigital linewidth,single or double IDT structures at 300 nm interdigital linewidth)were prepared on silicon-based substrates based on the optimal piezoelectric composite structure.The frequency response test results showed that the addition of the center grating reduced the insertion loss slightly on the basis of maintaining the original device frequency;the double IDT structure reduced the insertion loss significantly;and the decrease of the interdigital linewidth increased the frequency significantly.Finally,the AlN thin film with or without ZnO buffer layer was deposited on the diamond substrates to prepare the SAW resonators and its properties were investigated.The results showed that the addition of ZnO buffer layer improved the crystal quality and piezoelectric properties of AlN thin film on the diamond substrates,and the quality factor of the SAW resonator was increased from 412.53 to 761.26 at the frequency of 7.49 GHz after adding ZnO buffer layer.The innovative works achieved in this thesis are as follows:(1)the optimized ZnO buffer layer thickness for the preparation of high performance AlN thin films is obtained on silicon-based substrates;(2)By comparing SAW resonators with or without center grating,and single or double IDT structures,it's concluded that the insertion loss of the device is effectively reduce by the optimal composite structure piezoelectric thin films and the double IDT structure on silicon-based substrates;(3)the addition of ZnO buffer layer on the diamond substrates effectively improves the piezoelectric performance of the AlN thin films and the quality factor of the SAW resonators.This thesis proposes a method of using ZnO buffer layer to improve the performance of AlN thin films,which improves the performance of SAW resonators to some extent,and provides a certain theoretical and experimental basis for preparing high frequency SAW resonators.