Research On IDT Structure Optimization And SAW Devices

Surface acoustic wave(SAW)devices have been used more and more widely in the fields of communication,sensing,and biomedicine.Especially in the 5G information era,the rapid development of mobile communication technology has put forward higher requirements for the performance of SAW devices.How to reduce insertion loss on the basis of improving the frequency of SAW devices has become the current research hotspot and difficulty.As one of the cores of SAW devices,the optimal design of interdigital transducer(IDT)greatly affects and determines the performance of the device.This paper combines modeling and simulation analysis with device preparation and testing to explore the realization of SAW devices with high frequency and low insertion loss.In this paper,the simulation software COMSOL was used to construct a two-dimensional model of uniform interdigital transducer(IDT)with a wavelength of 24?m based on lithium niobate(128°-YX LiNbO₃),The modal and admittance analysis was carried out.A SAW delay line model in an IDT structure with a operating frequency of166.3MHz was constructed,and the forward and reverse insertion losses were-9.02 d B and-9.65 d B,respectively,which proved the bidirectional transmission characteristics of IDT structure.By analyzing the influence of electrode material,electrode thickness and metallization rate of IDT on the performance of the device,the corresponding structural parameters were determined.In order to avoid the bidirectional transmission loss of the IDT structure,the floating electrode unidirectional transducer(FEUDT)structure was introduced for simulation analysis,the SAW delay line model of the FEUDT structure with the same wavelength of 24?m was constructed.The forward and reverse insertion losses were-5.43 d B and-9.19 d B,respectively,which proved the unidirectional transmission characteristics of the FEUDT structure can effectively reduce the insertion loss of the device.In the experiment,the SAW device was fabricated on a 128°-YX LiNbO₃substrate using integrated circuit technology such as ultraviolet lithography according to the simulation structure.The device's operating frequency was 160MHz,which was close to the simulation result of 166.28 MHz.The forward insertion loss of-25.68 d B was reduced by about 8 d B compared with the reverse insertion loss of-33.10 d B,indicating that it had unidirectional transmission characteristics.In short,the experimental results verified the accuracy of the simulation results.In order to realize the high frequency of SAW devices,a two-dimensional model of SAW device in the FEUDT structure with a wavelength of 3.6?m was constructed using COMSOL on an aluminum nitride(AlN)/silicon(Si)substrate with high phase velocity.The simulation results show that the operating frequency of the device can be increased to 1.38 GHz,and the FEUDT structure still maintains unidirectional transmission characteristics in high-frequency devices.According to the simulation structure,the FEUDT and IDT structure SAW devices with the same wavelength of 3.6?m were fabricated on Al N/Si piezoelectric substrate using electron beam exposure(EBL),and the operating frequency all reached 1.4 GHz,which was basically consistent with the simulation results,and the insertion loss of SAW device with FEUDT structure was about 11d B lower than that with the IDT structure.Therefore,applying the FEUDT structure of the unidirectional transducer to the high-frequency SAW device can effectively reduce the insertion loss and thereby improve the device performance.In addition,the influence of the number of interdigital electrode pairs on the transmission performance of SAW device was studied.The relative bandwidth of the main peak decreased with the increase of the interdigital electrodes number,which provided a solution for the bandwidth control of SAW devices.