岛型振动膜电容式微超声传感器研究

Capacitive micromachined ultrasonic transducer(CMUT) offers several performance advantages such as low impedance, wide bandwidth, small size, high sensitivity and potential for integration with electronics. They are ideally suitable for medical imaging and diagnostics. Currently, compared with conventional piezoelectric transducers, CMUT has lower transduction efficiency. Aimming to intravascular ultrasound (IVUS) imaging, this research project mainly focuses on CMUT with island membrane structure for increasing the transmit pressure without degrading the receive sensitivity. Island membrane CMUT can solve the trade-off between transmit and receive performance when designing the flat membrane configuration. In this project, the static and dynamic behavioral of transducer will be investigated based on theories of thin plates and electrostatic actuation, then, an equivalent circuit of CMUT with island membrane will be constructed. On this basis, the influence of the geometrical parameters on the characteristics of transducer will be studied to obtain the best design parameter. Furthermore, the microfabrication process of CMUT with island membrane will be developed to achieve the prototype of transducer. Finally, characterization measurements of transducer will be performed. This work will provide theoretical and technical basis for the design and fabrication of CMUT with island membrane, and will promote the practical application of capacitive micromachined ultrasonic transducer in IVUS system.

电容式微超声传感器具有声阻抗低、频带宽、体积小、灵敏度高和易于电子集成等特点，在医学成像等领域具有良好的应用前景。但是目前电容式微超声传感器与广泛使用的传统压电式超声传感器相比发射效率较低。本项目以血管内超声成像为应用目标，提出了一种具有岛型振动膜的新型微超声传感器结构，能够在提高其发射效率的同时不降低接收灵敏度，以解决平膜电容式微超声传感器输出声压提高而接收灵敏度降低的矛盾。本项目采用弹性薄板振动理论及静电驱动相关理论，研究岛型膜微超声传感器物理参数与其静态、动态特性的关系，建立传感器等效电路模型；在此基础上研究传感器结构参数对其性能的影响规律并进行优化设计；研究岛型膜传感器制作的微加工工艺；最终进行传感器的性能测试和实验。本项目的研究将为岛型膜电容微超声传感器及阵列的设计、制作提供理论和技术基础，对推动传感器在血管内超声系统中的实际应用具有重要意义。

在MEMS和超声学交叉领域，电容式微超声传感器（CMUT）声阻抗值较低，易与水、空气介质相匹配，具有较宽的频带，阵列一致性好，在空气耦合式超声检测和医学超声成像等领域具有重要的应用前景。在基金资助下，针对电容式MEMS超声传感器开展了相关研究。通过研究传感器工作时其振动薄膜的电、力、声相互作用，分别建立了具有单膜阵元结构和多膜阵元结构的传感器非线性等效电路模型，并进行了仿真分析和验证；研究传感器驱动电压和结构参数对性能的影响规律，对具有不同阵元规模和阵元形状的传感器的结构参数及阵列参数进行了优化设计；基于表面硅加工工艺制作完成了CMUT传感器阵列，器件的岛型振动膜由多晶硅和金电极组成；通过阻抗测试、薄膜振动测试以及声学测试实验，测试结果与设计基本一致，传感器的谐振频率为1.5MHz-2MHz。本项目中电容式微超声传感器阵列的研制，为传感器在超声成像系统中的实际应用提供了理论和技术基础。