Performance Improvement Of Piezoelectric Micromachined Ultrasonic Transducer And Its Array

The Piezoelectric Micromachined Ultrasonic Transducer(PMUT)is an ultrasonic transducer based on MEMS technology.Compared with traditional ultrasonic transducers,it has many advantages: higher frequency,imporved impedance matching,and easy formation of array.Therefore,it is widely used in ultrasound imaging,such as motion capture,fingerprint sensing and so on.The imaging clarity of PMUT and its array for ultrasonic imaging is directly related to tranmitting performance and receiving performance of PMUT.In current research,the imaging clarity of PMUT remains to be improved.In order to improve the transmitting and receiving performance of piezoelectric micromachined ultrasonic transducer and its array,according to the theory of thin plate vibration,the intrinsic frequencies under tension or stiffness domained piezoelectric micromachined ultrasonic transducers of different modes are deduced in detail.Simulation and manufacture of PZT membrane based piezoelectric micromachined ultrasonic transducer cell are carried out to verify the four resonant modes.For further performance improvement,transmitting sensitivity and receiving sensitivity of Sc Al N membrane based PMUT cell were optimized by finite element method from the aspect of Sc doping concentration,film thickness and top electrode radius of Sc Al N film.To study the dynamic transmitting performance,this paper analyzes the radiate power,on-axis sound intensity and sound directivity of the PMUT cell.Then,this paper conduct study of top electrode radius effect on PMUT resonant modes,and put forward the method of applying(0,2)model to improve transmitting performance of PMUT.In this paper,Sc Al N piezoelectric micromechanical ultrasonic transducer array is modeled and optimized for application of fingerprint sensing.Analysis of cell number,cell spacing,array clamping effect on sound pressure and directivity of PMUT array is performed,combined with comparison of(0,1)mode and(0,2)mode,thus further explain advantage of applying(0,2)mode for piezoelectric micromachined ultrasonic transducers.Preliminary fabrication of Sc Al N piezoelectric micromachined ultrasonic transducer array was carried out and the performance of Sc Al N film is characterized.