Study On Surface Acoustic Wave Devices Based On Piezoelectric Thin Films With Novel Structure

Surface acoustic wave?SAW?devices have been widely used in commercial field for decades,because of the advantages of strong alternative,miniaturization and high sensitivity,and so on.With the development of modern technology,the demand for SAW devices,which have the properties of high operating frequency,low insertion loss and high temperature stability,becomes more and more urgent.In this paper,the characteristics of SAW devices with ZnO films or AlN films on different substrates are analyzed by finite element method?FEM?,which provides the theoretical basis for the fabrication of SAW devices with excellent characteristics,such as high frequency and high electromechanical coupling coefficient?k²?.The main contents are described briefly as follows:?1?The propagation properties of Love waves,which are excited by the SAW delay lines based on the multi-layered structure of?110?ZnO films and?110?AlN films on diamond substrate,are investigated by COMSOL multi-physics software.The admittance,phase velocities?v_p?,electromechanical coupling coefficients?k²?,and temperature coefficient of delay?TCD?of Love wave are numerically analyzed.Furthermore,the characteristics of 0th Love wave excited by the periodic multi-layered structure of IDT/[?110?ZnO/?110?AlN]_N/Diamond are calculated.The results show that the 0th Love wave has the largest k² of 4.32%in IDT/?110?ZnO/?110?AlN/Diamond structure associated with a phase velocity of 3848 m/s and TCD of 22.1 ppm/?as h_ZnO=3.4?m and h _AlN/?=0.19.Meanwhile,the k² values of Love wave in IDT/[?110?ZnO/?110?AlN]_N/Diamond structure increase with the increasing of the layer period N;however,due to the different temperature properties of ZnO films and AlN films,the value of TCD decreases with the increasing of layer period N for RH=0.2,and the temperature compensation is not realized for RH=5.?2??110?ScAlN/R-sapphire substrate structure is promising for high frequency acoustic wave devices.The characteristics of SAW devices based on IDT/?110?ScAlN/R-sapphire structure are analyzed by FEM,such as the mass sensitivity?S_m?,reflection coefficient?r?and impedance,as well as the effects of propagation direction of acoustic waves,the layer of mass perturbation,and the electrode on the SAW characteristics.The results show that the Rayleigh wave and Love wave are excited along[001]direction and[100]direction of?110?ScAlN films,respectively.The k²_max of 0th Rayleigh wave is 3.57%at h/?=1,corresponding to v_p and S_m of 3676 m/s and 23.6 m²/kg,respectively.The k²_max of 0th Love wave is 6.39%at h/?=0.33,associated with v_p of 4644 m/s and S_m of 38.3 m²/kg.?3?Novel SAW devices,combined IDT/?110?ZnO/SiO₂ layered structure with 2D phononic crystals?PCs?,are modeled.And the characteristics of SAWs are investigated by 3D-FEM,in which the PCs with various sizes are embedded in different positions of SAW delay lines.The results show that the properties of SAWs are mostly influenced by the PCs embedded in ZnO films and on the propagation path of acoustic wave,such as the insertion loss and the energy accumulation of SAWs.