Research On Cantilever Based MEMS Acoustic Pressure Sensor

Cantilever is one of the most commonly used structures in Microelectromechanical System(MEMS)sensing field.It usually demonstrates low mechanical strength and is easy to be deformed,especially when it works under resonant state,its deformation will be further amplified.As a result,the sensors based on this structure have potential to obtain high sensitivity.At the same time,compared with the electrical displacement detection methods,the optical methods possess advantages of high displacement detection accuracy,strong anti-electromagnetic interference ability and wide applicable range.Obviously,if a sound pressure sensor is constructed by using a resonant MEMS cantilever beam as the acoustic energy transduction structure and detecting its vibration with optical means,high performance sound pressure detection can be anticipated due to the combination of their advantages.Based on this concept,the structure design of the sensor is systematically studied from different application requirements and corresponding verification experiments are carried out.As for the structure design of the acoustic energy transduction cantilever beam,the equivalent mechanical vibration analysis model of the cantilever is built,based on which the effects of various structural parameters on its working performance are analyzed in details for atmospheric and underwater application scenarios.At the same time,the frequency response characteristics of different cantilever beams upon exposure to sound pressure are simulated by using multi-physics coupled finite element analysis method.In order to meet different application requirements,given the same resonant working frequency,a variety of cantilever design strategies are proposed and validated via simulation mainly focusing on the control and optimization over both of the detection sensitivity and the working bandwidth.Moreover,two optical displacement detection methods are designed to detect the acoustic pressure induced cantilever deflection during operation with high sensitivity:(1)Assembled Fabry-Perot(F-P)interference cavity.It consists of the top surface of the MEMS cantilever and the optical fiber end face.Its working principle and signal demodulation method are analyzed,and the amplitude as well as the contrast variation of its time domain signal under certain operation conditions are deduced by numerical simulation.(2)Integrated waveguide-ring resonator coupling structure.In this case,the waveguide is fabricated onto the same substrate of the cantilever,whilst the ring resonator is directly arranged onto the cantilever.Its working principle for the cantilever beam vibration detection is analyzed systematically,and the output spectrum variation of the waveguide-ring resonator coupling structure caused by the cantilever deformation under static load is also studied by COMSOL multi-physical coupling simulation.For proof-of-concept demonstration,six kinds of cantilever structures with different properties are fabricated using MEMS process.On this basis,several acoustic pressure sensors are constructed through using the F-P interferometer based displacement detection mechanism.From their acoustic pressure sensing performance test under atmospheric condition,high sensitivity detection for the acoustic waves with different frequencies have been obtained,validating the effectiveness of the proposed structure design.At the same time,the angular detection performance of the as-fabricated sound pressure sensors are also characterized,and the influence of the device package on its detection performance is discussed as well.