适用于宽带滤波器的I.H.P.SAW基底结构优化设计

Design Optimization of I.H.P.SAW Substrate Structure for Wideband Filter

超级高性能(I.H.P.)SAW器件因具有优异的品质因数(Q)值及温度稳定性而备受关注。为用于宽带滤波器的研发,对双层结构(Cu电极/Y旋转5°切LiNbO_(3)压电层/SiO_(2)功能层/Si衬底)的I.H.P.SAW基底结构设计进行了研究。考虑质量加载效应,结合电极与压电层界面上的应力与自由电荷分布特点,采用精确的有限元/边界元法(FEM/BEM)理论进行研究。利用多层结构的连续性边界条件,计算多层复合格林函数以及谐振器导纳值,寻求谐振点与反谐振点之间最大频率差以优化基底结构尺寸。计算结果表明,对金属化比为0.5,结构周期(λ/2)为2μm的器件,当功能层、压电层、电极层厚分别为0.15λ、0.2λ、0.0375λ时,谐振频率点为880 MHz,反谐振点为1018 MHz,由此可获得138 MHz的最大频率差。此结论为应用于宽带滤波器的I.H.P.SAW器件的设计提供了指导。

The Incredible High Performance(I.H.P.)SAW devices have attracted much attention due to their excellent Q characteristics and temperature stability.In order to develop the wideband filter,the design of a 2-layered I.H.P.SAW substrate structure(Cu electrode/5°Y-rotated LiNbO_(3)piezoelectric layer/SiO_(2)function layer/Si substrate)is studied in this paper.Considering the mass loading effects,and combining the distribution characteristics of stress and free charge on the interface between the electrode and the piezoelectric layer,the accurate Finite Element Method and Boundary Element Method(FEM/BEM)is used in the study.Using the continuity boundary condition of the multilayer structure,the composite Green’s function and the admittance of the resonator are calculated accurately.The maximum frequency difference between the resonance point and anti-resonance point is sought to optimize the substrate structure size.The calculation results show that the device with the metallization ratio of 0.5 and structure period(λ/2)of 2μm has a maximum frequency difference of 138 MHz between the resonant frequency point of 880 MHz and the anti-resonant frequency point of 1018 MHz when the thicknesses of the function layer,piezoelectric layer and the electrode layer are 0.15λ、0.2λ、0.0375λ,respectively.The conclusion provides guidance for the design of I.H.P.SAW devices for wideband filters.