基于弛豫铁电单晶的温补型声表面波特性和损耗机理研究

The propagating characteristics of surface acoustic wave (SAW) on novel relaxor based ferroelectric single crystals obtain ultra-high electromechanical coupling factors, however, there are some drawbacks, such as large propagation loss and poor temperature stability. This project proposed temperature compensated SAW structure with such single crystals to improve comprehensive performance of SAW devices. . Firstly, simulate and optimize the SAW propagating characteristics by optimizing PT components, polarization direction and cut-type of the crystals, and investigate the influence of domain structure, phase transitions, doping and annealing on the performance. Then, further improve and re-design the structure parameters of one-port SAW resonator, properly select electrode and top layer materials for suppressing "leaky wave", body scattering and spurious waves. Finally, establish the simulation model, design and fabricate broadband, low loss and stable temperature stability of prototype SAW filters. . Through the implementation of this project, we aim to achieve precise analysis of propagating characteristics of the layered structure, reveal loss mechanisms and take effective measures to reduce losses, finally found an initial SAW device fabrication process for providing basic research of tunable RF SAW filters.

新型弛豫铁电单晶的SAW具有超高的机电耦合系数，这是实现超宽带SAW滤波器的必要条件，但是，谐振器工作频率附近存在寄生峰干扰，品质因数和温度稳定性也亟待提高。基于此，本项目围绕该单晶开展温补型SAW传播特性和损耗机理研究。首先通过理论计算SAW传播特性与单晶组份，极化方向和切型的关系，研究缺陷、铁电畴、相变和掺杂等对SAW性能的影响，以指导基片的优化处理；然后，优化设计温补型谐振器，减小器件结构损耗，优选电极种类和厚度，减小“漏波”损耗，并抑制体波散射和杂波，设计温补层结构和优化制备工艺，抑制导波干扰，并减小粘滞吸收和散射损耗；最后，理论分析超宽带、低损耗和温度稳定性良好的滤波器工作原理，并制备出原型器件。通过本项目的实施，精确分析该单晶温补结构中SAW传播特性，揭示损耗的物理机制并尽量降低损耗，初步建立起SAW器件制备的工艺流程，为通信体射频前端可调滤波器的研究奠定基础。

本项目拟研究基于驰豫铁电单晶的温度补偿型SAW传播特性和损耗机理，从而实现超宽带、低损耗和温度稳定性良好的原型器件。理论分析了二元(PMN-PT)和三元体系 (PIN-PMN-PT) 弛豫铁电单晶的沿(001),(110)和(111)极化的，不同组份、切型和Mn掺杂的情况下，声表面波在单晶中以及层状结构中的传播特性，包括：传播速度Vp、K2及速度温度系数TCV，优化设计谐振器的结构参数，优化电极层和温补层结构设计，以进一步抑制寄生杂波干扰，获得了工作模态纯净且高Q值(>85)的谐振器，最后，根据实测的SAW谐振器的基本性能，设计了适用于该单晶体系的滤波器的拓扑结构图，通过对组成滤波器的各谐振器的参数进行优化，获得了低损耗的超宽带SAW滤波器性能。