Afshari Esmaeil, Houri Samer, Verplancke Rik, Rochus Veronique, Cauwe Maarten, Gijsenbergh Pieter, Op de Beeck Maaike
IMEC-Interuniversity Microelectronics Centre, Kapeldreef 75, 3001 Leuven, Belgium.
Centre for Microsystems Technology (CMST), Technologiepark-Zwijnaarde 126, 9052 Ghent, Belgium.
Sensors (Basel). 2025 Jun 30;25(13):4074. doi: 10.3390/s25134074.
The motivation of this work is to enable the use of piezoelectric micromachined ultrasonic transducer (PMUT)-based implants within the human body for biomedical applications, particularly for power and data transfer for implanted medical devices. To protect surrounding tissue and ensure PMUT functionality over time, biocompatible and hermetic encapsulation is essential. This study investigates the impact of Parylene F-VT4 layers of various thicknesses as well as the effect of multilayer stacks of Parylene F-VT4 combined with atomic layer-deposited nanolayers of AlO and HfO on the mechanical and acoustic properties of PMUTs. PMUTs with various diameters (40 µm, 60 µm, and 80 µm) are fabricated and tested both as stand-alone devices and as arrays. The mechanical behavior of single stand-alone PMUT devices is characterized in air and in water using laser Doppler vibrometry (LDV), while the acoustic output of arrays is evaluated by pressure measurements in water. Experimental results reveal a non-monotonic change in resonance frequency as a function of increasing encapsulation thickness due to the competing effects of added mass and increased stiffness. The performance of PMUT arrays is clearly influenced by the encapsulation. For certain array designs, the encapsulation significantly improved the arrays' pressure output, a change that is attributed to the change in the acoustic wavelength and inter-element coupling. These findings highlight the impact of encapsulation in modifying and potentially enhancing PMUT performance.
这项工作的动机是使基于压电微机械超声换能器（PMUT）的植入物能够在人体内用于生物医学应用，特别是为植入式医疗设备进行能量和数据传输。为了保护周围组织并确保PMUT长期功能正常，生物相容性和密封封装至关重要。本研究调查了不同厚度的聚对二甲苯F-VT4层的影响，以及聚对二甲苯F-VT4与原子层沉积的AlO和HfO纳米层的多层堆叠对PMUT机械和声学性能的影响。制作了各种直径（40 µm、60 µm和80 µm）的PMUT，并分别作为独立器件和阵列进行测试。使用激光多普勒振动测量法（LDV）在空气和水中对单个独立PMUT器件的机械行为进行表征，而通过在水中进行压力测量来评估阵列的声学输出。实验结果表明，由于附加质量和刚度增加的竞争效应，共振频率随封装厚度增加呈现非单调变化。PMUT阵列的性能明显受到封装的影响。对于某些阵列设计，封装显著提高了阵列的压力输出，这种变化归因于声波波长和元件间耦合的变化。这些发现突出了封装在改变并潜在增强PMUT性能方面的影响。
