Research On Piezoelectric Micro-machined Ultrasonic Transducer 2D Array Based On AlN Film

As a key device in the acoustic-electric transition process,ultrasonic transducer has been widely applied in the fields of industry,national defense and medical treatment.Its material and structure have always been the focus of academic research.High-frequency PMUT with high sensitivity and spatial resolution has broad prospects in the field of medical diagnosis and treatment.As an environment-friendly and lead-free piezoelectric material,aluminum nitride?AlN?material has been gradually applied to PMUT due to its compatibility with CMOS process and good stability in high frequency band.However,the low piezoelectric constants of AlN piezoelectric thin films limit the development and application of AlN-based PMUT.Therefore,it is necessary to optimized design the structure and array to meet the performance requirements.In this paper,the influence of the size of the circular double laminated bending vibration PMUT with AlN material as the piezoelectric layer on the performance of the PMUT is studied,and the size of the structure is optimized.The directivity of the AlN transducer array is studied and optimized.Finally,the 8×8 transducer array with good performance is obtained.Send performance of AlN-based PMUT is studied.According to analysis of the working principle and vibration mode of transducer,the model of transducer is simplified reasonably.The theoretical model is established and the main factors affecting the performance of the transducer are explored.A finite element model is established,and the transducer is simulated with finite element method for the size parameters of transducer including transducer radius,top electrode radius,piezoelectric layer thickness and vibrating layer thickness.Through simulation,it is found that the resonant frequency of the transducer is directly proportional to the thickness of each layer,and is inversely proportional to the square of the transducer radius.When the top electrode radius is about 65% of the transducer radius,the resonant amplitude of the transducer reaches the maximum.When the thickness ratio of the vibrating layer Si to the piezoelectric layer AlN is about 0.6,the resonant amplitude of the transducer reaches the maximum.And the larger the transducer radius is,the larger the resonant amplitude of the transducer is.According to the simulation results,the structure size of the transducer is determined,and its performance is simulated and compared with the original model.The resonance amplitude in air is raised from 0.1?m to 0.34?m,the k_e in air is 27.16%,the k_e in water is 11.93%,the dynamic equivalent resistance in water is about 1k?,and the maximum value of SVL is146.22dB.The directivity of single-element and multi-element transducer array is studied.Through theoretical analysis,the directivity function of single-element transducer array is deduced.It is found that the factors affecting the directivity of transducer array are transducer radius and operating frequency.The directivity,acoustic attenuation and stability are taken into account to optimize the single element.The directivity is further improved by multi-element transducer array.After comparing several basic arrays,the square array is selected for optimization.According to the directivity function of multi-element square array,the factors that affect the directivity of the transducer array are the element spacing and the number of elements.The directivity parameter of the transducer array is optimized by changing the element spacing and the number of elements.The final structure size of the transducer array is determined according to the optimization results,area and filling efficiency.Finally,the acoustic pressure distribution of the optimized transducer array is simulated visually.It is found that the optimized transducer array has an ideal sound pressure distribution,good far-field sound field distribution,and an obvious directivity with an about 86?m radiation beam width.The directivity is good,the main-lobe of which is sharp.The -3dB beam width ???_-3dB of the main-lobe is about 9 degrees,and the side-lobe level is about 0.228.