The Research On The Key Technology Of Aluminum Nitride Piezoelectric Thin Film Ultrasonic Oil Film Measurement Transducer

In the industry, mechanical parts mostly rely on lubricant oil to reduce friction and wear on the surface of the relative movement.The reasonable oil film thickness is the key to determine that mechanical equipment can work normally. Therefore, it can warn to ensure normal operation before the mechanical unit is damaged if constantly testing the oil thickness between important components.Compared with other measurements, there are no limitations of transparency and electrical isolation for ultrasonic measurement method, so it has a wider application prospect.This paper researches the key technology of ultrasonic measurement system,it includes :preparation of AlN piezoelectric thin film transducer,theoretical research on ultrasonic exciting and receiving circuits and make the PCB.(1)Based on the acoustic wave propagation theory, we research the feature of acoustic wave propagation and its reflection coefficient theory in the two-layer structure.Based on the two-layer structure,setting up the measurement model for different oil film thickness,the resonant model and spring model,namely through the oil film stiffness and the resonant frequency to measure its thickness.(2)Comparing with different methods to deposite AlN piezoelectric thin film,choosing reactive magnetron sputtering to deposite C axis oriented AlN piezoelectric thin film on the stainless steel by reactive magnetron sputtering. Designing the process of depositing AlN piezoelectric thin film and explore the factors that influence its orientation,such as: sputtering pressure, nitrogen gas flow ratio,the middle layer,etc. By using AFM to characterize thin film surface morphology,XRD to characterize growth orientation for thin film,successfully depositing(002) orientation AlN thin film on the steel and Si..(3)Design ultrasonic transimitting and receiving circuit of the center frequency of 2.5MHz and the circuit is based on the STC12C5412 AD. The emission part includes the impulse transmission circuit,amplifying circuit, MOSFET driving circuit and ultrasonic exciting circuit.The receiving part includes amplifying limiting circuit and amplifying circuit. Besides,theoretically discuss the high-frequency ultrasonic excitation circuit.We can take advantage of the triode transistor avalanche effect to design MARX avalance circuit to excite high frequency ultrasonic transducer.