Design Of Capacitive Micromachined Ultrasonic Transducer Based On Si-SOI Wafer Bonding

Capacitive Micromachined Ultrasonic Transducer (CMUT) has the advantages of wideband, high mechanical-electrical conversion efficiency, mass production, well impedancematching with medium and the merits that it is various in sizes, suitable for manufacturinglarge array, which has pressing needs and wide application in the fields of industrial control,environmental protection equipment, medical equipment, aeronautics and astronautics,military weapons. In view of the current demand for CMUT and its bright applicationprospect, the study of CMUT has extremely important scientific value and practical meaning.Based on capacitance principle and combined with the current fabrication level, a newstructure with intricate wires has been designed in order to reduce parasitic capacitance anddecrease the difficulty of detection capacitance as well as increase receive sensitivity. A seriesstudy about the principle, design method and the key technology of process has been carriedout, which provides the technological accumulation and experimental support for the designof device and process technology. The concrete research contents of this paper are as follows:(1) The theoretical analyses of CMUT are described in this paper. In mechanical aspect,it also presents the analysis of membrane vibration under the uniformly distributed load andelectrostatic force, according to the vibration theory; From the view of electro-mechanical, aparallel plate capacitor model was proposed in order to obtain the expression of collapsevoltage, output pressure, receiving sensitivity. Through the method of electromechanicalanalogy, equivalent circuit model of the device are established to get performance parametersincluding mechanical impedance of membrane, device capacitance, transfer ratio and so on.(2) After simulated by MATLAB, the relationship between performance parameters anddesigned size is analyzed and the structure size is determined; The collapse voltage, natural frequency and maximum ac voltage under operational mode of the proposed structure issimulated by single field and coupling field simulation of ANSYS; The basic transmitting andreceiving performance of the designed device has been obtained throughMATLAB/SIMULINK.(3) According to current process level，a technological process and layout have beendesigned, and the device has been fabricated. The key process and steps have been verified bythe experiment，which includes：thermal oxidation, ion implantation, low temperature waferbonding of Si and SOI, etching of Si and on SOI.(4) Preliminary tests of the device is conducted by laser microscope, micro-systemanalyzer impedance analyzer, including the morphology test, stress test, vibration frequencytest, emission properties test and consistency test, which verified performance of thetransducer.