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摘要:
体声波谐振器的有效耦合系数和品质因数决定了体声波滤波器的整体性能。有效耦合系数依赖于叠层结构和压电材料。而品质因数高度依赖于损耗机制，主要为电学损耗和声学损耗。对于固态装配型谐振器（SMR），声学损耗主要为透过衬底的能量泄漏。为提高SMR的品质因数，改进了布拉格堆叠结构，使纵波和剪切波同时被约束在压电堆叠结构中，以减少声能对衬底的泄漏。同时，为抑制谐振腔的杂散模式，优化了布拉格结构顶层薄膜厚度，器件色散特性由Ⅱ型变为Ⅰ型。通过仿真和实验表明：基于优化布拉格结构的SMR性能得到了明显改善。
Abstract:The effective coupling coefficient and the quality factor of the bulk acoustic wave resonators determine the overall performance of bulk acoustic wave filters. The effective coupling coefficient is dependent on the layer stack structure, especially the piezoelectric material, while the quality factor is highly dependent on the loss mechanism, including the electrical and acoustical loss. For solidly mounted resonator (SMR), the acoustic losses mainly include the acoustic leakage to the substrate. In this work, to enhance the quality factor of the SMR, the structure of the Bragg layer is optimized to reduce the acoustic energy leakage to the substrate. Through optimizing the Bragg stack, the longitudinal and shear waves can be confined in the piezoelectric stack simultaneously, and the quality factor at the anti-resonance frequency is highly improved. Moreover, to suppress the spurious mode of the resonator, the thickness of the top layer of the Bragg is optimized to change the device dispersion characteristic from type II to type I. Experimental results show that the performance of the SMR is improved greatly based on the optimized Bragg structure.
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Key words:
- bulk acoustic wave /
- solidly mounted resonator /
- Bragg /
- shear wave /
- high quality factor
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图 1 传统布拉格结构纵波和剪切波传输特性
Figure 1. Transmission characteristics of longitudinal and shear waves of traditional Bragg structure
图 2 优化的布拉格结构和Ⅰ型色散优化布拉格结构的纵波与剪切波传输特性
Figure 2. Optimized Bragg structure, and transmission characteristics of longitudinal and shear waves of optimized Bragg structure for type Ⅰ dispersion
图 3 3种布拉格结构的SMR器件阻抗和品质因数对比
Figure 3. Comparison of impedance and quality factor between SMR devices of three Bragg structures
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