Construction Of SAW Devices With Low-Loss Based On Structural Optimization Of Single-Phase Unidirectional Transducer

With the rapid development of communication technology,whether in science or industry,the demand for low-loss surface acoustic wave（SAW）devices for RF front-end fabrication has increased significantly.How to reduce the insertion loss of SAW devices while increasing their operating frequency has become a hot and difficult area of research.As one of the cores of SAW devices,the design and optimization of the structure of the interdigital transducer（IDT）directly affects the performance of SAW devices.This paper combines simulation analysis and experimental verification to explore and investigate the implementation of high frequency,low loss SAW devices.Firstly,a 2D model of a single-phase unidirectional transducer with controlled electrode width（EWC/SPUDT）based on lithium niobate（128°Y-X LiNbO₃）with a wavelength of 16μm and an operating frequency at 240 MHz was constructed using COMSOL to analyze the effects on the reflectivity of different electrode materials and electrode thicknesses.The model of the EWC/SPUDT structure SAW device was constructed and the forward insertion loss of-12.50 d B and the reverse insertion loss of-14.65 d B were obtained,demonstrating the unidirectional transmission characteristics of the EWC/SPUDT structure.Due to the limit ofλ/8 transconductance electrode preparation process in the EWC/SPUDT structure limits its operating frequency,this paper introduces a high-frequency single-phase unidirectional transducer（SPUDT）structure,constructs a high-frequency SPUDT structure SAW device model,and increases the operating frequency to 490 MHz using its second harmonic characteristics,with forward insertion loss of-8.51 d B and reverse insertion loss of-19.40 d B,obtaining a unidirectional propagation of-11 d B.Then,SAW devices with an electrode width of 2μm in the EWC/SPUDT structure were prepared using a UV lithography process at 128°Y-X LiNbO3 according to the simulated structure,and the test devices operated at 235 MHz with a forward insertion loss of-19.47 d B and a backward insertion loss of-36.56 d B,achieving a unidirectionality of-17 d B.Under the same lithography process conditions,a SAW device with a high-frequency SPUDT structure was prepared and tested with an operating frequency of 486 MHz in the second harmonic mode with a forward insertion loss of-11.91 d B and a backward insertion loss of-31.89 d B,achieving-20 d B unidirectionality.Therefore,both structures use 128°Y-X LiNbO3 as the piezoelectric functional layer,and the high-frequency SPUDT structure increases the frequency of the device while reducing the loss of the device.Finally,in order to realize high-frequency,low-loss SAW devices,the high-frequency SPUDT structure is introduced into the high-sound velocity piezoelectric material ScAlN,and a simulation model is constructed to analyze the effects of piezoelectric material thickness,wavelength and electrode thickness on the second harmonic characteristics.On the basis of this,the conventional IDT and high-frequency SPUDT structure SAW devices were prepared and tested and analyzed by electron beam exposure（EBL）process,and the operating frequency of both devices was 1.4 GHz,and the insertion loss of the SPUDT structure SAW devices was reduced by 10 d B compared with the IDT structure.Therefore,the design of high frequency SPUDT structure can effectively reduce the insertion loss of SAW devices and thus improve the performance of the devices.