Preparation And Application Research Of Piezoelectric Thin Film Ultrasonic Transducer

In recent years,the rapid development of acoustic emission detection technology can reflect the country's industrial development level to a certain extent,and its importance is self-evident.The signal generated by the acoustic emission source can be transmitted to the surface of the material through the medium and then detected by the transducer.Piezoelectric materials are widely used in acoustic emission transducers because of their good stability,high detection sensitivity and integration.Among them,PVDF film and AlN film are the two most widely used piezoelectric film materials.The PVDF film has a high piezoelectric response and good flexibility,but it is currently mainly used in low-frequency fields such as heartbeat and breath detection.The speed of sound velocity on the surface of the AlN film is fast,and it has the obvious characteristics of integration and arraying of detectors.Therefore,increasing the application frequency of PVDF devices and modifying AlN films to improve piezoelectric performance has been a hot research topic at home and abroad.In this paper,the design,simulation and experimental verification of PVDF-based ultrasonic transducers are studied.At the same time,research on modified AlN thin film materials is carried out to meet the next stage of development of integrated arrayed ultrasonic sensors.The main work of this paper is as follows:?1?Design and manufacture PVDF transducers,and perform finite element simulation and experimental analysis.A polyimide film coated with copper electrodes is used as the protective layer and the electrode extraction layer.The shape of the transducer is designed to be rectangular.The welding place is composed of a hollow rivet and an O-type terminal,and an external force is applied to the PVDF transducer pair.The response of the action was simulated.It was found that after applying a constant force,the PVDF transducer will output a voltage in a short time,and then the amount of charge will remain unchanged;at 25KHz,85KHz accessories frequency will have a higher voltage output;with As the thickness of the film increases,the output voltage also gradually increases.The designed and manufactured PVDF transducer has a good response to the excitation of the knock signal,lead-break signal and fixed ultrasonic vibration source.The main peak frequency of the lead-break signal of the test response is about 100KHz,which is consistent with the actual situation.?2?To study the effect of Er element on the modification of AlN thin film and the film preparation process on the film performance.Discuss the influence of sputtering power,sputtering temperature and other factors on the growth and properties of ErAlN film?002?crystal orientation.ErAlN thin films were grown in the nitrogen content of0.194⁰.446,and it was found that when the energy is sufficient and the deposition rate is fast,the?100?crystalline film tends to grow,and when the energy is high and the deposition rate is slow,the?002?crystalline direction tends to grow Film,so by adjusting the process parameters,the growth structure of the film can be controlled.The piezoelectric coefficient d₃₃ of the ErAlN film with the optimal?002?crystal orientation is 9.4pm/V,while the d₃₃ of the pure AlN film is 5.5pm/V.It can be seen that the doping of Er element can improve the piezoelectric response of the AlN film.?3?For Er doped AlN thin films,interdigital transducers are designed and prepared.The effects of exposure time and development time on the preparation of interdigital transducers were studied.The optimal exposure time was 3.1s and the development time was 7.0s.The interdigital transducer structure was realized on the ErAlN film.?4?The ErAlN-based surface acoustic wave ultrasonic transducer was designed,prepared and tested.The anti-resonance frequency simulated for the interdigital ErAlN-based ultrasonic transducer is 190.79MHz,and the resonance frequency is190.84MHz.As the thickness of the piezoelectric layer increases,the resonance frequency of the device increases;as the thickness of the Mo electrode layer increases,the resonance frequency decreases;the resonance peak of the surface acoustic wave transducer is located at about 180MHz.A capacitive ErAlN-based ultrasonic transducer was prepared and tested accordingly.The test showed that the transducer had a good response to the 33KHz vibration signal.