MEMS Vector Hydrophone Based On Silicon Nano-film Micro-nano Integrated Technology Research

With the development of underwater detection technology,vector hydrophone based on micro-electromechanical systems(MEMS)have gradually become the important subject of underwater acoustic research due to its miniaturization,low manufacturing cost,array ability,mass production,and ease of integration.However,traditional cilium vector hydrophone has problems such as inaccurate spatial positioning of long-distance acoustic signals and low sensitivity in low-frequency detection.Therefore,this paper proposes a MEMS vector hydrophone based on silicon nano-film,via introducing silicon nano-membrane instead of the original square resistance structure as the pressure-sensitive unit,the piezoresistive coefficient is improved,which is beneficial to improve the detection sensitivity of the hydrophone.The silicon cilium and silicon dioxide cross beams were integrated by semiconductor technology,which improves the alignment accuracy and solves the long-standing consistency error caused by the secondary integration of cilium.Based on the cilium vector hydrophone,this article introduces the theory of underwater acoustic propagation and the principle of hydrophone vibration pickup.Based on the piezoresistive MEMS vector hydrophone,introduces the detection and sensing principles of the hydrophone.The piezoresistive effect was studied through the surface depletion mechanism,and establishes the giant piezoresistive model.Through theoretical analysis of the hydrophone mechanics model,combined with finite element simulation analysis,optimizes the structure size of the hydrophone,and the structure design of the hydrophone was completed.Through statics simulation and modal simulation,it is concluded that it can theoretically increase the sensitivity and has a wider working frequency band,which proves the feasibility of the scheme.Finally,the specific process flow and key process steps of the scheme are introduced in detail,and the preparation of the integrated vector hydrophone is completed.Observed by scanning electron microscope(SEM),the length of cantilever beam is 2478),the width of cantilever beam is 1218),and the thickness of cantilever beam is 3.38),which are basically consistent with the design index,verifies the rationality of the process design.The resistance test of the piezo resistance obtained a very linear I-V characteristic curve.The resistance value of the piezo resistance on the four cantilever beams all reached 7000,indicating that the ohmic contact and the consistency are well,which is in line with the vector hydrophone Design requirements.At the same time,the piezoresistive coefficient of silicon nano-film is 3.12×10^-9(6^-1,which is higher than that of traditional P-type bulk silicon([110]crystal orientation)4.35 times,and the improvement of the piezoresistive coefficient can effectively improve the sensitivity of the hydrophone,which further proves that the solution can effectively optimize the performance of the hydrophone.