硅基反铁电材料相变应变致动高频、高Q薄膜体波谐振器基础研究

Film bulk acoustic wave resonators (FBAR) play an important role in mass sensor, of which detection limit is determined by resonate frequency (f) and Q value. In this work, the antiferroelectric thin film (Pb,La)(Zr,Ti)O3（PLZT）is used as an electrostrictive layer in FBAR, and device escapes completely the dependence on the inverse piezoelectric effect due to the phase transition induced strain effect in PLZT, the operating frequency and Q value (especially the Q value in liquid) could be increased to a large extend due to the faster response, the lower internal loss and the larger strain (including the longitudinal strain and the transverse strain) in PLZT, which is novel method to enhance sensor sensitivity. The antiferroelectric FBAR has higher f and Q vaule (f≥10 GHz；Q in gas≥2500，Q in liquid≥500), compared to the f (1~3 GHz) and Q value (Q in gas~1000，Q in liquid≤100) of piezoelectric FBAR；Moreover, the better fatigue resistance antiferroelectric thin film renders the FBAR higher reliability and longer life. This project will study the heterogeneity integration and phase transition mechanism in PLZT thin film, and the resonation and theoretical model in FBAR, which can offer the mass sensor technology theory and method.

薄膜体波谐振器（FBAR）是用于微质量探测技术的核心器件，其谐振频率和Q值决定了探测极限。本项目采用反铁电薄膜(Pb,La)(Zr,Ti)O3（PLZT）作为FBAR的执行单元，利用其相变应变效应作为器件的致动机制，基于PLZT本身的快响应、低内耗和大应变（纵向和横向）等优势，使器件谐振频率和Q值得到大幅度提升（频率≥10 GHz；气相Q值≥2500，液相Q值≥500），突破了传统压电式FBAR谐振频率（1~3 GHz）和Q值（气相Q值~1000，液相Q值≤100）瓶颈，为FBAR敏感特性的增强提供了新思路。同时，反铁电薄膜PLZT优异的抗疲劳特性可进一步提高FBAR器件的可靠性和使用寿命。本项目针对PLZT反铁电薄膜的异质成膜机理和电致相变调控，以及FBAR器件的相变谐振特性和电学、力学模型等基础科学问题展开深入研究，为高灵敏微质量探测系统的开发和应用提供基础理论和关键技术支撑。

传统薄膜体声波谐振器利用材料压电效应实现声波振荡，其工作频率受限于压电层厚度。本课题组创新性地提出了基于反铁电材料的相变致动效应的薄膜体声波谐振器（FBAR），通过采用溶胶-凝胶工艺制备反铁电功能材料，实现了晶圆级薄膜的异质集成并进行性能表征，XRD测试表明该薄膜具有明显的111晶向，结合AFM和SEM分析，可以得到完整的表面形貌特性；在此基础上借助有限元分析软件COMSOL，对反铁电相变致动的FBAR器件特性进行模拟，建立FBAR三明治结构仿真模型，对激励电场、纵向和横向位移的各种振动模态进行三维分析，通过分析电场和声波传播的耦合情况和反铁电薄膜的电机耦合特性、反铁电体在电场作用下的变形情况，确定了谐振器的几何尺寸和单元结构参数，形成了高频PLZT反铁电薄膜体声波谐振器的工艺方案；绘制了基于反铁电功能材料的器件版图，通过光刻、刻蚀等MEMS工艺制备了基于三明治结构的功能器件，测试得到器件的串联谐振频率fs=1.147GHz，并联谐振频率fp=1.209GHz，带宽为62MHz，机电耦合系数K2=12.65%，为后期的应用拓展奠定了一定的基础。