Research On Temperature Compensated Acoustic Wave Device

The development of modern communication technology has put forward higher requirements on the performance of RF filters and duplexers,such as higher operating frequency and higher stability.As widely used core devices,the operating frequency and temperature stability of surface acoustic wave?SAW?devices and bulk acoustic wave?BAW?devices have become important measures of device quality.In this thesis,the characteristics of temperature compensated SAW devices and temperature compensated BAW devices based on ZnO thin films or Al N thin films are simulated and analyzed by finite element method.The purpose is to provide a design and implementation scheme for the development of SAW and BAW devices with high temperature stability and high frequency.The main contents are described briefly as follows:?1?Using the finite element simulation tool COMSOL,the simulation models of IDT/?110?ZnO/?111?Diamond and IDT/?110?Al N/?111?Diamond were established,and the propagation characteristic and temperature characteristic of Love waves on these structures are discussed in detail.Furthermore,a finite element model of IDT/?110?Al N/?110?ZnO/?111?Diamond temperature compensation structure is established.The temperature coefficient of frequency?TCF?,electromechanical coupling coefficient?k²?and phase velocity?vp?of the first-order and second-order Love modes in the structure are systematically investigated.The results show that TCF of the first-order Love wave is close to zero associated with a vp of 7478 m/s and a k² of 1.8% as h ZnO=0.5um and h_AlN =0.608um;and the TCF of the second-order Love wave is close to zero as h ZnO=1um and h_AlN=1.4um,corresponding to vp and k² of 10243 m/s and 0.68% respectively.It means that this structure can be used to develop high-quality SAW devices.Finally,the effects of electrode materials and electrode thickness on the IDT/?110?Al N/?110?ZnO/?111?Diamond temperature compensation structure were analyzed.The results show that proper selection of electrode materials and electrode thickness can improve the performance of SAW devices.?2?This thesis also carried out the research of temperature compensated BAW resonator based on PI flexible substrate.Based on the analysis of the effects of PI flexible substrate on BAW resonator,a finite element model of a temperature compensated BAW resonator with a Mo-ZnO-Mo-SiO₂-PI structure was established.The temperature coefficient of frequency and electromechanical coupling coefficient of the first-order and second-order BAW modes of the structure are systematically investigated.Furthermore,a finite element model of the temperature compensated BAW resonator with the Mo-Al N-Mo-SiO₂-PI structure is established,and the influence of temperature compensation layer on the structure was analyzed by finite element method.The results show that the TCF of second-order mode in Mo-ZnO-Mo-SiO₂-PI structure is close to zero associated with k² of 6.3% as h_ZnO=4um and h_SiO2=3.2um;and the TCF of the first-order mode in Mo-Al N-Mo-SiO₂-PI structure is close to zero associated with k² of 4.7% as h_AlN=4um and h_SiO2=0.78 um.It means that these structures can be used to develop high-quality BAW devices.