薄膜体声波谐振器的力敏特性研究

薄膜体声波谐振器(FBAR)力传感器作为一种新型的谐振式传感器，力敏特性是其设计原理。以FBAR微加速度计为例研究了工作在纵波模式，采用具有纤锌矿结构的AlN作为压电薄膜的FBAR，施加应力载荷后，其弹性常数改变导致FBAR谐振频率偏移的力敏特性。首先，采用有限元(FEA)静力学仿真，得到惯性力载荷作用下集成在硅微悬臂梁上的压电薄膜的应力分布；选取最大应力值作为载荷，基于第一性原理计算纤锌矿AlN的弹性系数与应力的关系式，预测惯性力载荷作用下AlN弹性系数的最大变化量。其次，采用谐响应分析，对比空载和不同惯性力载荷作用下FBAR微加速度计的谐振频率和偏移特性，预测FBAR微加速度计的加速度-谐振频率偏移特性。最后仿真分析得到:惯性力载荷作用下，FBAR微加速度计的谐振频率向高频偏移，灵敏度约为数kHz/g；其加速度增量-谐振频率偏移特性曲线具有良好的线性度。

Force-sensing characteristics of film bulk acoustic resonator

Film bulk acoustic resonator (FBAR) force sensor is regarded as a new type of resonant sensor ,whose design is based on force-frequency characteristics of FBAR. This paper aims to analyze the force-frequency characteristics of FBAR that works in the longitudinal mode and adopts wurtzite AlN as piezoelectric thin film, whose resonance frequency shift results from the elastic constant under the stress load by taking an FBAR micro-accelerometer as an example. First, the stress distribution of the piezoelectric thin film of FBAR which integrated on FBAR micro-accelerometer under the inertial forces was obtained from applying the static simulation of finite element analysis. Then the maximum stress value selected as stress load, combining first principles to calculate the relation ship between elastic coefficient and stress of wurtzite AlN, so that the maximum variation of AlN elastic coefficient under the stress load can be predicted. Next, the resonance frequency with shift properties of FBAR micro-accelerometer are compared under different stress loads with the analysis result of harmonic response so as to predict the frequency characteristics and tendency of FBAR. By analyzing FBAR under the stress loads, its resonance frequency can be concluded to shifts to a higher one, and FBAR micro-accelerometer sensitivity is about kHz/g, which indicates the good linearity of acceleration increment-frequency shift characteristic curve.