Research On Capacitive Micromachined Ultrasonic Transducer For Gas Sensing

Gas detection is one of the most active techniques in the field of instrumentatio n science,which plays a key role in many applications such as medicine,biology and national defense.With the new type of gas sensor on the stage of real-time and fast detection,fast recognition of complex gas,high sensitivity,miniaturization and other targets also pose many challenges to the performance of gas sensor.Thanks to the rapid development of micro-electro-mechanical machining system(MEMS),capacitive micro-ultrasonic transducer(CMUT)has shifted from its traditional field of ultrasonic technology to more sensing applications,such as gas sensing,humidity sensing,etc.,which are inseparable from its resonance frequency affected by many physical quantities.Compared with the traditional resonant gas sensor,CMUT has many advantages,such as low minimum detection limit,small diaphragm mass and many sensitive elements in the array.In recent years,researchers at home and abroad pay a lot of attention to the advantages of large quantity and small diaphragm mass.Taking the gas detection of capacitive micromachined ultrasonic sensor as the application target,this paper has carried out the work of the design and simulation of sensing unit,the design of CMUT array gas sensor,the analysis of resonance characteristics and gas sensing characteristics,the processing of CMUT gas sensor and gas detection experiment,etc.the specific research contents include:1.This paper analyzes the gas detection principle of CMUT,simulates the basic working parameters of the sensitive unit.Based on the electromechanical coupling model of calculating mass sensitivity and quality factor,the energy dissipation mechanism of the sensing element is studied to improve the sensing performance,and the size parameters of the CMUT sensing element applied to gas sensing are determined.2.Based on the technology of silicon glass anode bonding,this paper designs the sensitive unit with gold wire channel to realize the electrical connection;designs the silicon dioxide and monocrystalline silicon composite film to achieve the insulation purpose while optimizing the quality factor;for the purpose of mixed gas detection,a row and column addressing array gas sensor is designed,which is designed through the staggered electrode design.Finally,the manufacturing process of c MUT gas sensor i s established.3.Aiming at the gas sensing application of CMUT,the influence of electrostatic force and stress on the resonance frequency and mass sensitivity of the diaphragm is studied.Through the gas sensing experiment,it is verified that the membra ne displacement is in the scope of large deflection deformation,and the stress greatly improves the membrane sensitivity.4.The sensors were modified and characterized,and the organic and inorganic gas sensors were tested.By analyzing the response curve of real-time acquisition,the sensitivity of the gas sensor to the device is evaluated.Compared with the traditional CMUT gas sensor,the quality sensitivity of the device in this paper is significantly improved.The linear fitting results of the response curve show that the linear relationship between the frequency response and the concentration of the device is good.