Simulation And Process Design Of Capacitive Micro-electromechanical Ultrasonic Transducer Arra

Ultrasonic imaging technology is widely used in many fields.Ultrasonic transducer is the core device in ultrasonic imaging system.Capacitive Micro-electromechanical Ultrasonic Transducer(CMUT)based on MEMS(Micro Electromechanical system)technology has the characteristics of wide frequency band,high electromechanical conversion efficiency,high sensitivity,easy integration with CMOS circuit,easy matching with working medium impedance and easy fabrication of large array.The CMUT vibration element model is established based on COMSOL multi physical field simulation software.Firstly,it is simulated and optimized,and then a new vibration element structure is designed by reducing the effective gap between the upper and lower electrodes,Finally,the optimized model is encapsulated into app interface.On this basis,the focusing performance of CMUT phased array is simulated,and 1 × 16 element CMUT one-dimensional linear array.The sacrificial release process is selected as the processing process.Combined with low-cost materials,the process flow design is proposed,and the mask required by the process is designed by L-edit software.The specific research contents are as follows:(1)The vibration displacement and vibration frequency of the circular film were analyzed according to the film vibration model;the modal mass,modal spring constant,damping constant,capacitance,collapse voltage and other parameter relations were analyzed according to the parallel plate capacitance model;The equivalent circuit of the receiving mode analyzes the electromechanical transmission ratio,sensitivity and bandwidth.(2)The diaphragm structure was simulated and optimized,and the steady-state analysis,modal analysis,harmonic response analysis and transient analysis of the vibration element were carried out by COMSOL software under the electromechanical field and pressure-acoustic physical field,and the simulation results were compared with theoretical calculations.draw conclusions by comparison.After verifying the feasibility of the structural design through simulation,the simulation software interface is encapsulated according to the above physical field model.(3)The phased array model is established by COMSOL software,and the effects of array element size,number and spacing on the focusing performance and axial sound field intensity of the transducer are studied.The larger the size of the array element,the better the focusing performance and sound field intensity.The more the number of array elements,the better the focusing performance,but the sound field intensity has nothing to do with the number of array elements.When the array spacing is less than or equal to half wavelength,the focusing performance and sound field intensity reach the best.(4)The process steps and their advantages and disadvantages of three different process design schemes are discussed,and then the process design of this paper is proposed.The mask patterns of sacrificial layer,diaphragm layer and metal layer suitable for two-inch silicon wafers were designed using L-edit software.The prepared reticle has been applied to the processing technology of CMUT ultrasonic transducer.