Performance Degradation Analysis And Reliability Evaluation Of MEMS Flow Sensor Based On Physics Of Failure

Micro electro mechanical system(MEMS)flow sensors have developed rapidly in recent years due to the advantages of miniaturization,low power consumption,high reliability and high measurement accuracy,and are widely used in various flow measurements.Whether the sensor can reach the expected working life is mainly considered in the current life tests for MEMS sensor,which contains the following characteristics: due to the high cost of long-term experiments,the method of testing structures is mainly used to conduct related experiments instead of life tests at the sensor device level;due to commercial confidentiality,long-term life test results of MEMS sensors are rarely published publicly;due to the lack of standards in the field of MEMS sensors,different manufacturers have different processes and procedures for manufacturing sensors based on the same principle.Above all,the reliability data of MEMES is hard to be obtained,which poses a great challenge to the reliability research of MEMS flow sensors.Therefore,it is necessary to study on physic model-based reliability modeling and assessment method of MEMS flow sensors to provide theory and method support for its safe and reliable service.For the above problems,in this thesis,based on the sub-topic of the National Key Research and Development Program,the reliability model of MEMS thermal flow sensor for the specific failure mechanism is established combined with the finite element simulation,and the analysis of performance degradation and reliability evaluation are carried out.The main research contents are as follows:(1)Considering the effect of contaminants on the measurement results of the flow sensor,a particle deposition model commonly used for dust deposition in pipes is introduced to establish the relationship between the amount of contaminant deposition and factors such as atmospheric pressure,temperature,and gravity.A finite element model of the MEMS flow sensor considering contaminants is developed using COMSOL software.The relationship between contaminant thickness and sensor measurement error is determined based on simulation data.Based on the degradation model,a corresponding reliability model is established and an arithmetic analysis is performed for the flow sensor applied to the air intake tract of an automobile.(2)Considering the effect of thermal stress on the reliability of heterogeneous material interfaces,finite element simulation of the bonding interface of heterogeneous materials using COMSOL software to obtain thermal stress simulation data of the interface,and the relationships between the thermal stresses and thermal expansion coefficient,temperature,and Poisson's ratio are determined based on finite element simulation data.The reliability of the silicon-glass bonding interface is evaluated using a load-strength interference model in combination with bond strength data.(3)For the plastic deformation of the structure,the sensor shell is considered to be subjected to pressure and viscous force in the fluid.A fluid-solid coupling simulation model is established using the finite element method,and based on the data obtained from the simulation model,the relationship between the stress and the shell size as well as the fluid flow rate is determined.Combined with the yield strength of the shell material,the reliability analysis is performed using the boundary model.