5G通信技术的高速、大容量数据传输对射频滤波器提出了“大带宽、高频率、高带外抑制、小型化”等苛刻要求，传统的压电体材料声表面波（SAW）滤波器方案已经不能满足5G发展的需求。多层压电复合结构以其丰富的设计维度和高效的声电耦合成为重要的声表面波新材料，是近年来5G滤波器研发的重要方向，但该结构中复杂的杂散响应给滤波器设计提出巨大挑战。因此，本文从诠释多层压电复合结构声传播规律出发，通过构筑多层压电复合材料与优化电极结构，发展出SAW器件中各种杂散模式的抑制技术，增强SAW滤波器性能，满足5G通信应用需求。针对瑞利模式恶化滤波器通带平坦度的问题，本文通过研究不同LiNbO3切向下瑞利波的机电耦合系数随电极厚度的变化，分析瑞利波的传播特性，发现有别于传统体材料的15°Y切，多层压电复合结构在LiNbO3切角优化至19°~22°Y切时出现大的瑞利波抑制窗口，为大带宽滤波器制备提供了具有更大工艺容差的新型压电复合材料。基于此在20°Y-X LiNbO3/SiO2/Si结构中成功制备了带宽20.1%的滤波器，该器件在较大电极厚度范围内均展现出平坦的通带响应。针对高阶模式破坏滤波器带外抑制的问题，本文通过研究不同Si取向对32°Y-X LiNbO3/SiO2/poly-Si/Si结构中高阶模式的影响，揭示了高阶抑制的机理，即当Si剪切波声速小于高阶模式声速时，高阶模式会与Si剪切波耦合导致声能泄漏从而被抑制。传统Si(100)衬底无法实现高阶抑制，而Si(110)和Si(111)可以分别在面内取向角α为18°~60°和14°~36°时抑制高阶模式。构建了以α = 45°的Si(110)为衬底的压电复合结构滤波器，完全消除了带外杂散响应，带外抑制达28.3 dB。围绕滤波器小型化的需求，在32°Y-X LiNbO3/SiO2/SiC结构中发展出独立梯形结构的双通带滤波方案。利用高声速SiC的强声波反射特性增强了高阶水平剪切波的激发强度；通过调控电极结构，解决了瑞利波和西沙瓦波的干扰问题。成功通过单一拓扑结构制备出频率分别为3.1 GHz和4.8 GHz的无杂散双通带滤波器。为了解决5G通信Sub-6 GHz频段滤波器“高频率、大带宽”的设计难题，利用高声速SiC基片与高质量LiNbO3薄膜构建了兼具高声速与高声电耦合效率的新型双层压电复合材料。通过设计LiNbO3薄膜厚度、取向与电极结构调控声传播路径，抑制了瑞利、高阶和横向模式，成功制备了分别覆盖n77、n78和n79全频段的高性能滤波器，实现了SAW滤波器在5G通信Sub-6 GHz频段的突破。

The high-speed and large-capacity data transmission of 5G communication technology has put forward the stringent requirements of “large bandwidth, high frequency, high out-of-band rejection and small size” on the radio-frequency (RF) filters. Conventional surface acoustic wave (SAW) filtering schemes using bulk piezoelectric materials are difficult to meet the demands for 5G development. The multilayer piezoelectric composite structure has emerged as a crucial and novel SAW material owing to its multi-dimensional modulation possibilities and high eletromechanical coupling, which has been an important research direction of 5G filters in recent years. However, the spurious modes existing in the multilayer piezoelectric composite structure pose great challenges for filter design. Therefore, starting from illustrating the acoustic propagation mechanism of the multilayer piezoelectric composite structures, this article has developed the suppression technologies of various spurious modes in the SAW devices by constructing the multilayer piezoelectric composite structures and optimizing the electrode structures. The performance of SAW filters has been augmented to meet the application requirements of 5G communication.In order to solve the problem of Rayleigh mode deteriorating the flatness of the filter passband, this paper investigates the electromechanical coupling coefficient of Rayleigh mode under different LiNbO3 cut angle as the electrode thickness changes and analyzes the propagation characteristics of the Rayleigh mode. Different from the 15°Y-cut of traditional LiNbO3 bulk materials, the multilayer structure exhibits large Rayleigh elimination window when the LiNbO3 is 19°~22°Y-cut. This result provides new piezoelectric composite materials with great process tolerance for the fabrication of 5G large-bandwidth filters. Based on this, SAW filter with a fractional bandwidth of 20.1% was successfully fabricated on 20°Y-X LiNbO3/SiO2/Si structure, which exhibits a flat passband response within a large electrode thickness range. Regarding the issue of higher order mode weakening the out-of-band rejection of the filter, this paper analyzes the effects of different Si orientations on the higher order modes in the 32°Y-X LiNbO3/SiO2/poly-Si/Si structure, and the mechanism of higher order mode suppression is revealed. That is, when the shear bulk acoustic wave velocities of Si are smaller than the velocity of the higher order mode, the higher order mode couples with the shear modes of Si, leading to the acoustic energy leakage and suppression. The traditional Si (100) substrate cannot achieve the suppression of higher order modes, while Si (110) and Si (111) can eliminate higher order modes when the in-plane orientation angle α is 18°~60° and 14°~36°, respectively. Then, a multilayer structure filter with Si (110) of α = 45° as the substrate was constructed, which completely eliminated the out-of-band spurious responses and its out-of-band rejection reaches 28.3 dB.Focusing on the demand for filter miniaturization, a dual-passband filter with a standalone ladder structure was developed on the 32°Y-X LiNbO3/SiO2/SiC structure. The strong acoustic reflection characteristics of SiC are used to enhance the excitation intensity of high order shear horizontal mode, while the interferences from Rayleigh mode and Sezawa mode are solved through electrode modulation. Then, spurious-free dual-passband filter with frequencies of 3.1 GHz and 4.8 GHz was successfully fabricated through a single topology structure.In order to overcome the design problem of “high frequency and large bandwidth” for sub-6 GHz band filters in 5G communication, high-velocity SiC substrate and high-quality LiNbO3 film were used to construct double-layer piezoelectric composite structures with both high acoustic velocity and high eletromechanical coupling. By controlling the LiNbO3 thickness, LiNbO3 cut angle and electrode structure, the Rayleigh mode, higher order mode and transverse mode were successfully suppressed. Spurious-free high-performance filters covering the full n77, n78 and n79 bands were successfully realized, achieving a breakthrough of SAW technology in sub-6 GHz bands of 5G communication.