Optimum Structure Design And Test Of Hydrophone Based On AlN Piezoelectric Film

The sonar is the core equipment for ocean monitoring,and the underwater acoustic transducer is one of the critical components of the sonar system.The receiving transducer is also called the hydrophone,and its quality level directly affects the monitoring capability of the sonar system.In this paper,a MEMS piezoelectric hydrophone based on aluminum nitride film（Al N）is proposed,and two structures of circular electrode type and ring electrode type hydrophone are designed.The MEMS piezoelectric hydrophone converts acoustic signals to electrical signals due to the positive piezoelectric effect.It has the advantages of small size,high sensitivity and high integration,and can be mass-produced,which improves the consistency and reduces the cost.This paper carries finite element simulation analysis,structural optimization,and process preparation of MEMS piezoelectric hydrophone.A new package structure and a weak signal extraction circuit are designed.Furthermore,the hydrophone’s basic characterization and performance test are finally completed.This work mainly includes the following contents:（1）The overall structure of the piezoelectric hydrophone is designed and simulated.The hydrophone’s resonance frequency and vibration mode are analyzed,and the relationship between the resonance frequency and geometric parameters of the hydrophone is obtained.The surface charge and stress distribution of the piezoelectric film subjected to acoustic excitation are calculated.The design of the hydrophone structure is optimized based on the results of finite element simulation analysis.（2）The fabrication process and corresponding method of piezoelectric hydrophone was designed and the mask layout was drawn.The piezoelectric hydrophone was fabricated using MEMS technology.The key process principles and quality control elements in the preparation process are analyzed in detail,and a mature process is finally formed.（3）The hydrophone was characterized and tested.First,the morphology of the hydrophone was observed by scanning electron microscope（SEM）.Next,the impedance curve of the hydrophone was measured by the impedance analyzer.Finally,the vibration modes,amplitudes and velocities of the hydrophones were tested by a POLYTEC microsystem analyzer.（4）The signal characteristics of the hydrophone are resolved.Then,the weak signal extraction circuit matched with the hydrophone is designed,and the function of each module of the circuit is introduced.The factors affecting the signal output in the packaging process are analyzed,and the packaging structure is improved.Finally,the extraction and amplification of the output signal of the hydrophone are completed.（5）A test platform for hydrophones was built in air and water,respectively.Based on the test platform,the performance parameters such as sensitivity,linearity,and noise resolution of the hydrophone in air and water were tested,respectively.And their performances were compared and analyzed.Based on previous research,the related preparation experience of MEMS hydrophone has been accumulated.In this paper,the new structure exploration and test method research of hydrophone have been carried out.As a result,the hydrophone has a sensitivity of-177 d B（re:1V/μPa）in 10-1000 Hz,and the nonlinearity is below 2% in different environments.