Piezoelectric micromachined ultrasonic transducers (p-MUTs) have been extensively utilized in medical imaging, range-finding, gesture recognition, and so on. However, the piezoelectric layer is dominated by the toxic Pb(Zr, Ti)O3, other materials possess inferior piezoelectric coefficients, and the traditional clamped diaphragm restricts the p-MUT response. In this work, lead-free ZnO films are doped by the vanadium nanostructures and are implemented to beam-island structure membranes, which are aimed to achieve non-toxic and high-performance p-MUTs. Firstly, the doping mechanism of ZnO is analyzed and the p-MUT structure is designed. Secondly, simulation based on the finite element method is conducted to evaluate the dynamic displacement of p-MUTs, after which prototypes are fabricated by the standard micromachined process. The effects of key fabrication parameters including O2 flow rates, sputtering targets, and annealing temperatures on V-doped ZnO films are investigated in detail. By using atomic force microscopy (AFM) and X-ray diffraction (XRD), the surface morphology and crystal structure of the films are analyzed respectively. Moreover, the piezoelectric properties are measured by piezo response force microscopy (PFM). The results indicate a piezoelectric coefficient as high as 194.5 pm/V, which is superior to most doped ZnO films. Finally, an experimental testing system is established to examine the p-MUT performance. Compared with the clamped diaphragm, the beam-island structure can acquire better electromechanical coupling and achieve range-finding successfully. This work provides a fine application prospect for enhancing the performance of lead-free p-MUTs.

中文翻译：

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在无铅压电微机械器件中实现 V 掺杂 ZnO 薄膜的制造和表征


压电微机械超声换能器 （p-MUT） 已广泛用于医学成像、测距、手势识别等。然而，压电层以有毒的 Pb（Zr， Ti）O3 为主，其他材料的压电系数较差，传统的钳位隔膜限制了 p-MUT 响应。在这项工作中，无铅 ZnO 薄膜被钒纳米结构掺杂并应用于束岛结构膜，旨在实现无毒和高性能的 p-MUT。首先，分析了 ZnO 的掺杂机理，并设计了 p-MUT 结构;其次，基于有限元方法进行仿真，评估 p-MUT 的动态位移，然后通过标准微机械加工工艺制造原型;详细研究了关键制造参数（包括 O 2 流速、溅射靶材和退火温度）对 V 掺杂 ZnO 薄膜的影响。通过使用原子力显微镜 （AFM） 和 X 射线衍射 （XRD），分别分析了薄膜的表面形貌和晶体结构。此外，压电性能通过压电响应力显微镜 （PFM） 测量。结果表明，压电系数高达 194.5 pm/V，优于大多数掺杂 ZnO 薄膜。最后，建立了实验测试系统来检验 p-MUT 的性能。与夹紧隔膜相比，梁岛结构可以获得更好的机电耦合并成功实现测距。这项工作为提高无铅 p-MUT 的性能提供了良好的应用前景。