Multi-Frequency Piezoelectric Micromachined Ultrasonic Transducers
Multi-Frequency Piezoelectric Micromachined Ultrasonic Transducers
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DOI：
10.1109/jsen.2019.2935158
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发表时间：
2019-12-01
影响因子：
4.3
通讯作者：
Ozevin, Didem
中科院分区：
文献类型：
--
作者：
Kazari, Hanle;Kabir, Minoo;Ozevin, Didem
本文设计、表征和测试了用于固体无损检测的多频压电微机械超声换能器(PMUT)。换能器工作在弯曲模式，并可调谐到三个不同的频率，即1 MHz，1.5 MHz和2 MHz。微结构层由氮化铝(AlN)作为有源敏感层，夹在金属电极和掺杂硅电极之间。PMUT设计有八角形和圆形膜。硅膜的振动有助于压电元件的能量转换。对换能器进行了数值建模，得到了它们的动态特性。压电多用户MEMS工艺(PiezoMUMP)被用于制造pMUT。机电特性分析表明，由于硅层和氮化铝之间的应力分布更加均匀，圆形设计比八角形设计具有更高的优值系数。结果表明，压电层应沉积到膜片变形拐点。这避免了由于相反极化而导致的信号抵消。通过实施非线性超声检测(NLUT)，评价了pMUT作为接收器检测蠕变损伤的性能。NLUT的基础是检测由于材料的非均质性而导致的固体中的高次谐波。由于pMUT的高窄带和低衰减特性，提高了NLUT检测亚波长损伤的分辨率，使得二次谐波得到了显著的放大。使用占地面积小的pMUT器件可以检测到更高的谐波，这是传统的压电式换能器所不可能做到的。这使得非线性测量具有更好的空间分辨率。
In this paper multi-frequency piezoelectric MEMS ultrasonic transducers (pMUTs) are designed, characterized and tested for nondestructive evaluation (NDE) of solids. The transducers operate in flexural mode, and are tuned to three different frequencies namely 1 MHz, 1.5 MHz and 2 MHz. The microstructural layers consist of aluminum nitride (AlN) as an active sensing layer sandwiched between metal and doped silicon electrodes. pMUTs are designed with octagonal and circular membranes. The vibration of silicon membrane assists piezoelectric element to convert energies. The transducers are modeled numerically to obtain their dynamic characteristics. Piezoelectric Multi-User MEMS Processes (PiezoMUMPs) are utilized to manufacture pMUTs. The electromechanical characterization shows that the circular design has higher figure of merit as compared to the octagonal design due to more uniform stress distribution transferred between silicon and AlN layers. It is demonstrated that the piezeoelectric layer should be deposited up to the inflection point of diaphragm deformation. This avoids the signal cancellation due to opposite polarization. The performance of pMUTs as receiver is evaluated to detect the creep damage by implementing nonlinear ultrasonic testing (NLUT). NLUT is based on detecting higher harmonics in solids due to heterogeneity in materials. Significant amplification in the second harmonics is obtained due to highly narrowband and low damping characteristics of pMUTs that improves the resolution of NLUT to detect subwavelength damage. Higher harmonics can be detected using small footprint pMUT device, which is not possible with conventional piezoelectric transducers. This allows better spatial resolution of nonlinear measurement.