Research On Key Technologies Of Capacitive Micromechanical Ultrasonic Transducer Array

Capacitive Micromachined Ultrasonic Transducer（CMUT）is composed of vacuum cavity capacitor structure arranged by certain rules.The top silicon film can realize the conversion of mechanical energy and electrical energy.Compared with the traditional piezoelectric transducer,it has the advantages of broadband,high integration and miniaturization.It has a broad application prospect in medical imaging,industrial nondestructive testing,underwater imaging and other applications.With the development of medical detection technology,three-dimensional ultrasound imaging system has developed rapidly.The key component to achieve high-resolution threedimensional imaging is the two-dimensional transducer array.Compared with twodimensional ultrasound imaging,real-time three-dimensional imaging can more comprehensively reflect the three-dimensional structure of biological tissues,which is conducive to the identification of complex biological tissues.Therefore,the research and development of CMUT array is of great value.In this paper,the theoretical analysis,model analysis,structural design,finite element simulation,optimization design,process preparation,performance test and underwater preliminary imaging experiment of CMUT are studied.The specific research contents are as follows:（1）According to the structure of CMUT,a simplified model is constructed,and then the working principle and electromechanical coupling of CMUT are analyzed.The relationship between the vibration frequency of the film and the radius and thickness of the film,the relationship between the displacement of the film and the radius and thickness of the film,and the relationship between the collapse of the film under bias voltage and the height of the cavity are obtained.The size of the CMUT unit is determined,and the complete CMUT design theory system is established,which provides important theoretical support for subsequent testing and optimization.（2）The modal analysis of CMUT unit is carried out in COMSOL,and the static characteristics are simulated.The modal analysis of CMUT unit is carried out in COMSOL,and the static characteristics are simulated.The simulation results are analyzed and compared with the theoretical results.MATLAB software is used to draw the three-dimensional directivity of the unit body related to the array element parameters according to the array directivity function.and the three-dimensional directivity,and the three-dimensional directivity graphics of the two-dimensional array related to the number,spacing and size of the array element,so as to determine the two-dimensional array parameters.（3）Si-SOI bonding process is used in the preparation of the sensor.According to the design of the sensor structure,the preparation process of the two-dimensional array is designed,and the mask is designed according to the process.The processing and packaging performance test of CMUT ultrasonic transducer are completed.（4）The metal interconnection of CMUT array is realized by silicon via,and the flip welding package is realized in CMUT array with via.