Relationship Between SiO₂ Strain Characteristics And The Performance Of High-temperature SiC Pressure Sensor

SiO₂ thin film has attracted tremendous attention in recent years for high-temperature SiC capacitive pressure sensors due to its superior physical and electrical properties.The calculation of capacitance for these sensors is highly dependent on the strain characteristics of SiO₂ film.However,its strain characteristics,particularly in high temperature,have rarely been studied.In this thesis,nanoindentation technology and ANSYS Workbench finite element software were carried out to obtain elastic parameters,plastic parameters,residual stress,and creep parameters of SiO₂ films.Furthermore,the influence of the strain characteristics for SiO₂ films on the performance of SiC capacitive pressure sensors at high temperature was also discussed.Firstly,the Young’s modulus of SiO₂ films with a thickness of 2.2μm grown by Low-pressure chemical vapor deposition were measured by nanoindentation tests.The results demonstrated that the Young’s modulus of SiO₂ film was 105.95 GPa,which decreased by 11.31%,14.63%,16.25%,and 18.17%after being treated at 600,700,800,and 900℃for one hour,respectively.Secondly,the plastic parameters of SiO₂ films were calculated in combination with finite element simulations and dimensional analysis.The results showed that the optimal value of representative strain was 0.091 in dimensional analysis.The yield strength of the SiO₂ film was 12.25 GPa,which decreased by 9.31%,11.51%,15.84%,and 16.24%after being treated at 600,700,800,and 900℃,respectively.Moreover,the SiO₂ films will“hardening”after high temperature treatment.Thirdly,the residual stress of SiO2 films in SiO₂/SiC structures were obtained based on Xu theoretical model and finite element simulations.The results demonstrated that annealing is effective in releasing residual stress of SiO2 films,while high temperature treatment will produce tensile stress of several hundred megapascals in the films.In addition,the creep stress exponent of SiO₂ films were found to decreased with increasing treatment temperature by using the nanoindentation technique in continuous stiffness model.Finally,the performance of SiC capacitive pressure sensors at high temperatures were studied by using transient thermal–structural coupling simulations.The results demonstrated that the internal stress values of the sensors were proportional to the ambient temperature and the stress concentration occurred at the Ti electrode.In respect to the electrical characteristics of the sensors,it was found that the zero drift of the sensors’capacitance were 0.003376%,0.003378%,0.003381%,and 0.003537%after being treated at 600,700,800,and 900℃for one hour,respectively.Futhermore,it was found that the elastic strain of the SiO₂ films had the greatest effect on the performance of the sensors,while the plastic strain and creep had little effect on the performance of the sensors by comparing the strain results of the SiO₂ films.However,the creep will be the dominant factor contributing to the failure of sensors if they are exposed to high temperatures for a long time.