Research On MEMS Piezoelectric Thin Film Ultrasonic Transducer

As the core sensing component of advanced ultrasonic testing instruments,MEMS Piezoelectric Thin Film Ultrasonic Transducer(PMUT)is the key to promoting the development of typical testing instruments in industrial manufacturing,energy and chemical,medical and health,defense and military applications.Its research can provide generic technology support for the application of sound pressure sensors in the fields of underwater acoustic detection and voice recognition in Io T,and can promote the development of high-accuracy acoustic detection equipment technology.Compared with other ultrasonic transducers,MEMS piezoelectric thin film ultrasonic transducers based on AlN piezoelectric thin films has good compatibility with CMOS process,green manufacturing process,good acoustic matching,high performance and low energy loss,which can be applied in extreme working conditions,while it has high technical barriers in research and development.In this paper,the research of MEMS piezoelectric thin film ultrasonic transducer is carried out,the basic principle of MEMS piezoelectric thin film ultrasonic transducer is elaborated,the basic theory and research model are deduced and established,the differential MEMS piezoelectric thin film ultrasonic transducer and mechanical-slit MEMS piezoelectric thin film ultrasonic transducer based on AlN piezoelectric thin film have been designed and manufactured,the performance test and application test of the PMUT devices have been completed.The main work of the dissertation is summarized as follows:(1)The basic working principle,research status,development trend,advantages and disadvantages of current mainstream MEMS ultrasonic transducer are analyzed and elaborated.The research significance and purpose of MEMS piezoelectric thin film ultrasonic transducer are clarified.(2)Based on the basic theory of ultrasonic transducer,the theoretical equations and research models of the MEMS piezoelectric thin film ultrasonic transducer in the sound field,piezoelectric film and thin-film ultrasonic transducer are deduced and established.The material of each functional layer of MEMS piezoelectric membrane ultrasonic transducer is analyzed and selected.The differential MEMS piezoelectric membrane ultrasonic transducer and mechanical-slit MEMS piezoelectric membrane ultrasonic transducer are designed.qualitative verification and analysis of the performance characteristics of the two kinds of geometric structure designs are carried out by finite element simulation software.(3)The integrated micro-nano fabricating technology for the two geometric structure MEMS piezoelectric thin film ultrasonic transducers is designed and optimized,including the design of the transducer layout,the manufacture process of device functional layer film,the etching process of Mo electrode and AlN piezoelectric film,the etching process of deep silicon on the back of the transducer and other process technologies,and the two kinds of MEMS piezoelectric thin film ultrasonic transduce are fabricated.(4)The performance of the fabricated MEMS piezoelectric thin film ultrasonic transducer is characterized,tested and analyzed,involved the device’s appearance,material characteristics,electromechanical characteristics,etc.The main factors that affect the performance of the PMUT device are analyzed through test results,including the influencing factors of the manufacture process performance of the device functional layer,the stress control during the device manufacture process and the PMUT device test method.Based on the application test platform of MEMS piezoelectric thin film ultrasonic transducer,the close-range ultrasonic ranging sensor test is carried out to verify the practical application of the PMUT device,in addition,measurement error and performance of ranging sensor test system are analyzed.