Research And Process Realization Of Capacitive Microelectromechanical Ultrasonic Transducer

Compared with traditional piezoelectric transducers,capacitive micromachined and micro-electro-mechanical ultrasonic transducers(CMUT)have excellent performance and broad application prospects.In this paper,the main research goal is to realize the structural design and process realization of the transducer used in air-coupled ultrasonic testing.Use COMSOL Multiphysics finite element analysis software to complete the simulation work of CMUT micro-elements and compare and analyze with theoretical research.Optimize the structure and mask layout of CMUT micro-element.Complete the simulation work of the CMUT array on the basis of the micro-elements research,and analyze the focused sound field characteristics of the transducer.A lowcost CMUT preparation process is designed based on the idea of sacrificial release process,and the process parameters are determined based on the simulation results to guide the preparation of CMUT.Firstly,the simplified model parameters are obtained based on the parallel plate capacitance model,and the relationship between the structural parameters of the CMUT vibrating film,such as the slice and thickness,and the resonance frequency,displacement voltage,static capacitance and mechanical sensitivity characteristic parameters are derived,and the acoustic radiation impedance characteristics of the CMUT micro-element are analyzed.Use COMSOL software to perform steady-state analysis,modal analysis,and harmonic response analysis of micro-elements in the electromechanical and pressure acoustic physics fields,and compare the simulation results with theoretical calculations.After verifying the feasibility of the structural design through simulation,a method of using SU-8 photoresist as the vibrating film was proposed,and the micro-element structure was optimized.Secondly,the CMUT phased array array is researched on the basis of determining the micro-element structure.The pulse reflection method is used to analyze the principle of the array imaging in the transmission and reception process,the generalized sound pressure,time delay excitation,normalization function,and the influence of the array element center distance,center frequency and number of the array elements on the directivity are analyzed.The phased array model was established using COMSOL finite element simulation software,and the excitation time and amplitude of the phased array element sound beams were determined.The influence of the center distance,center frequency,and number of array elements on the axial sound pressure of the transducer is studied in a two-dimensional space to ensure that the formed focused sound field has good characteristics in terms of focus depth and inspection efficiency.Finally,the advantages and disadvantages of the existing sacrificial release process and wafer bonding process are compared and analyzed.Combining theoretical and simulation research results,it is proposed to use Sur Pass 3000 to sacrifice the cavity and SU-8 as the method of vibrating membrane,and to design a low-cost CMUT preparation process.Discuss the manufacturing process in detail,determine the process parameters of each step,and provide a feasible plan for the preparation of the transducer.The results of CMUT theoretical analysis and finite element simulation show that the use of sacrificial release process to prepare the transducer can meet the design requirements.This topic helps to design a low-cost,high-yield capacitive micromachined and micro-electro-mechanical ultrasonic transducer.