Accelerated Stress Simulation And Failure Mechanism Analysis Of SiC Capacitive Pressure Sensor

SiC capacitive pressure sensor for high temperature,high pressure,impact,vibration and other extreme environment has good environmental adaptability,has a wide range of applications in scientific research and industry.In this thesis,stress analysis of SiC capacitive pressure sensor under various loads is carried out based on ANSYS finite element analysis software.According to the simulation results,an accelerated stress screening scheme of the sensor is proposed,and its failure mechanism is studied.Firstly,the finite element analysis model of SiC capacitive pressure sensor was established based on ANSYS Workbench platform,and the stress distribution of sic capacitive pressure sensor under single temperature,pressure,vibration and impact loads was solved.It is found that in the pressure range of the sensor,the temperature load has the greatest impact on the stress of the sensor.When the temperature reaches 900℃,the maximum stress of Si O2 film layer reaches 180 MPa,while the maximum stress of the sensor under a single vibration or impact load is not more than 1MPa.Secondly,the stress analysis of the sensitive element under a variety of load coupling is carried out.It is found that the coupling of high temperature and impact load will make the sensitive element produce far more than the stress amplitude under a single load,but there is no such phenomenon when other loads are coupled.When the temperature is 600℃and the impact load is 178.9Grms,the maximum instantaneous stress amplitude on SiC sensitive film reaches 1.4GPa,while the maximum stress amplitude of Si O2 layer under the sensitive film exceeds 330 MPa,and the maximum stress amplitude will continue to increase with the increase of temperature or impact load value.Finally,based on the finite element analysis results of the sensor,the acceleration stress conditions and different stress levels were determined,and the calculation method of acceleration factors under different stress levels was derived.On this basis,the accelerated stress screening scheme of SiC capacitive pressure sensor was designed.At the same time,the morphology of the ohmic electrode and the sensitive element structure of SiC sensor is analyzed,and the failure mechanism is studied.The main reason is that the ohmic characteristics of metal electrode are deteriorated due to a series of chemical reactions at high temperature,and the Si O2 bonding layer of the sensitive element structure is void,cracking and falling off due to thermal stress and process defects at high temperature.Finally,the reliability of the whole sensor is affected.