Design And Test Of Capacitive Micromachined Ultrasonic Transducer Linear Array For Underwater Imaging Applications

Ultrasonic imaging technology has extensive application prospects in medicaldiagnostic、nondestructive testing、ultrasonic microscope and underwater detecting and otherfields. Ultrasonic transducer is a core component of the ultrasonic imaging equipment.However, the traditional piezoelectric transducer has many limitations and does not meet therequirement of the modern ultrasonic imaging detection more and more. While capacitivemicromachined ultrasonic transducer (CMUT) recently become a research focus due to theadvantages of high mechanical-electrical conversion efficiency, wide band, well impedancematching with medium and suitable for manufacturing large array.With the research foundation of ultrasonic imaging theory and combined with the currentfabrication level, a one-dimensional linear array with16elements has been designed in thispaper. A series study about the principle, design method, process flow and performancetesting has been carried out. The concrete research contents of this paper are as follows:(1) The directivity pattern of the radiated sound field has been studied. Focal anddeflection delay principle of the ultrasonic beam, as well as spatial resolution and artifact hasalso been analyzed and researched.(2) The structure size of the sensitive cell is determined by simulation software ANSYS,and the performance parameters of working voltage, collapse voltage, static capacitance,dynamic capacitance and output current have also been analyzed. Based on the design ofsensitive cell, the elements spacing, element size and element number which have influenceon the directivity pattern of the linear array is also been analyzed, Finally, the structure size ofthe linear array is determined.(3) With the research foundation of anterior processing experience and combined with the current fabrication level, the process flow based on Si-Si bonding has been optimized andthe1-D CMUT linear array has been completed with the optimized process flow. Accordingto the application requirements of underwater imaging, the package structure with goodwaterproof property and transmission property is designed.（4）By testing the surface topography of the CMUT linear array, the measuring resultsshow that the design size is basically same as the obtained by actual measuring size, and thenthe accuracy and feasibility of the process flow is proved. The emission and receiveperformance of the ultrasonic transducer is been tested, and the influence on emissiontransducer with different DC value is also been analyzed. Then primary imaging experiment isdone by using the1-D CMUT linear array.