Design And Key Technology Research Of MEMS Capacitive Pressure Hydrophone

As the core device of underwater sound pressure detection,sound pressure hydrophone plays an important role in the fields of underwater sound detection,marine monitoring,and underwater military.The MEMS capacitive sound pressure hydrophone designed in this paper mainly uses a sensitive diaphragm to generate vibration under the action of sound waves,and converts the sound signal into an electrical signal to achieve the detection of sound pressure.Compared with piezo acoustic pressure hydrophones and fiber optic acoustic pressure hydrophones,which currently occupy a high market share,MEMS capacitive acoustic pressure hydrophone has good impedance matching with liquid media,low power consumption,high sensitivity,wide frequency band,and mass production(low cost).In this paper,we carried out the structure design,mechanical analysis,thermal viscosity acoustic simulation,process preparation scheme exploration and consistency test of the MEMS capacitive sound pressure hydrophone,mainly including the following work contents:(1)We have designed the whole structure of the capacitive sound pressure hydrophone,and carried out theoretical analysis and small-signal model analysis for the sensitive element of the vibrating film,at the same time the relationship between parameters such as diaphragm deformation,collapse voltage and resonance frequency and structure size was obtained.The structure size of hydrophone is determined by comprehensive consideration.(2)A thermal viscous acoustic analysis method was proposed for the small size capacitive sound pressure hydrophone operating in the low frequency band,that is,in the analysis process,the thermal and viscous damping effects of the hydrophone structure wall on the sound wave need to be considered.Then the thermalviscous acoustic multiphysics field was introduced in the process of finite element analysis.Through static analysis,modal analysis and acoustic disturbance analysis,important parameters such as diaphragm type variable,resonance frequency,internal instantaneous sound velocity,internal acoustic temperature change and receiving sensitivity of hydrophone were obtained.(3)The preparation of capacitive acoustic pressure hydrophone was processed using MEMS technology.Due to the large area and thin thickness of the hydrophone,the vibration film was very easy to be damaged during the preparation process.In the preparation process,different methods and different film materials were used for multiple attempts.It mainly included the use of sacrificial layer to prepare silicon dioxide vibration film by plasma enhanced chemical vapor deposition(PECVD),and adopted the method of anode bonding and thinning of SOI sheet and glass sheet to prepare single crystal silicon vibration film.Finally,a vibrating film with a flat surface and good quality is prepared by anodic bonding.(4)In order to isolate the electromagnetic interference in the environment,the capacitive sound pressure hydrophone was encapsulated in the designed electromagnetic shielding shell for testing.After testing multiple hydrophones with an impedance analyzer,the average value of the capacitance value of the hydrophone was 4.277 pF,the standard deviation was 0.153 pF,the average phase of the hydrophone was-89.129 °,and the standard deviation was 0.153 °.The test results proved that the capacitive acoustic pressure hydrophone prepared by the improved anode bonding process has good consistency.