Abstract Film bulk acoustic resonators (FBARs) are widely applied as gravimetric sensors for gas and biochemical analysis. For these devices, the sensing layer is usually coated on to the FBAR for qualitative analysis based on the frequency response according to the Sauerbrey relationship. Various polymers have been used as the sensing films for volatile organic compound (VOC) monitoring. The most significant works are focused upon developing sensing materials and optimizing the piezoelectric film to improve the performance of the sensors. However, the influence of the swelling stress upon the sensing film during vapor absorption on resonant frequency of the FBAR is often ignored. In this work, the influence of the swelling stress upon the frequency characteristics of the sensors based on polymer-coated FBARs have been investigated in detail. The elastic coefficient and acoustic wave velocity changes of the piezoelectric (AlN) layer in the FBAR in the presence of stress loads were calculated by the first-principle methods. In combination with the Mason model of the sensors, the resonant frequency shifts of the FBAR under swelling stress were obtained. The results show that the frequency shifts of the FBAR are enhanced with increased swelling stress that induce negative impacts upon the FBAR sensor-based operation. In order to improve the vapor sensing performance, the optimal thickness of the sensing film must be evaluated.

中文翻译：

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外部膨胀应力对基于聚合物涂层膜体声波谐振器 (FBAR) 的挥发性有机化合物 (VOC) 传感器频率特性的影响

摘要 薄膜体声波谐振器（FBARs）被广泛用作气体和生化分析的重量传感器。对于这些设备，通常将传感层涂在 FBAR 上，以根据 Sauerbrey 关系基于频率响应进行定性分析。各种聚合物已被用作挥发性有机化合物 (VOC) 监测的传感薄膜。最重要的工作集中在开发传感材料和优化压电薄膜以提高传感器的性能。然而，在蒸汽吸收过程中膨胀应力对传感膜的影响对 FBAR 谐振频率的影响往往被忽略。在这项工作中，已经详细研究了膨胀应力对基于聚合物涂层 FBAR 的传感器频率特性的影响。通过第一性原理方法计算了FBAR中压电（AlN）层在应力载荷下的弹性系数和声波速度变化。结合传感器的梅森模型，获得了膨胀应力下 FBAR 的共振频移。结果表明，FBAR 的频移随着膨胀应力的增加而增强，这会对基于 FBAR 传感器的操作产生负面影响。为了提高蒸汽传感性能，必须评估传感膜的最佳厚度。获得了膨胀应力下 FBAR 的共振频移。结果表明，FBAR 的频移随着膨胀应力的增加而增强，这会对基于 FBAR 传感器的操作产生负面影响。为了提高蒸汽传感性能，必须评估传感膜的最佳厚度。获得了膨胀应力下 FBAR 的共振频移。结果表明，FBAR 的频移随着膨胀应力的增加而增强，这会对基于 FBAR 传感器的操作产生负面影响。为了提高蒸汽传感性能，必须评估传感膜的最佳厚度。