Design And Fabrication Of High Temperature And Fast Response Thin Film Heat Flux Sensor Based On MEMS Technology

In the design and development of aerospace equipment,there are many state parameters such as surface temperature and heat flux of hot end components,such as turbine blades,combustion chambers and flame tubes,which need to be accurately measured.Heat flux and its distribution are important input parameters for the design of hot end components.Thin film heat flux sensor thickness is only in the order of micro and nano,has the advantages of almost no interference to the measured parts,small size,fast response speed,high sensitivity,has great application value in the design and development of aerospace equipment.In order to improve the sensitivity of the heat flux sensor,this thesis proposes a thermal resistance layer with reticular cavity structure,and then two kinds of thin-film thermoelectric reactor heat flux sensors with thermal resistance layer structure were prepared based on MEMS technology.The influence of thermal resistance layer material and thermal resistance layer structure on sensor sensitivity and response time is systematically studied.The main work of this thesis is as follows:（1）On a 12×12×0.65 mm alumina ceramic substrate,a thin film thermoelectric reactor type heat flux sensor is designed with 192 pairs of serpentine series Pt/PtRh10thin film thermocouples with a single wire width of 100μm,a wire length of 1mm and a wire spacing of 100μm as the sensitive layer and four thin films with a length of 10mm and a width of 1mm（SiO₂,YSZ,SiN）as the thermal resistance layer.The heat transfer simulation of thermal resistance layer with different structures and materials is carried out by Comsol simulation software,the simulation results show that the thermal insulation effect of the designed mesh cavity structure is better than that of the ordinary thin film thermal resistance layer.The simulation results provide a basis and reference for the development of heat flux sensor.（2）The thermoelectric reactor films were prepared by MEMS and thin film technology,and the samples were annealed at 800℃for 60 min.After annealing,the average resistivity of the thermoelectric reactor is 2.05×10^-5Ω/cm,and the average Seebeck coefficient of the Pt/PtRh10 thermocouple is 8.28μV/℃.The rigid mask was used to prepare the thermal resistance layer film,and some samples were subjected to high temperature thermal cycling at 1000℃atmosphere for 60 min to investigate the high temperature resistance of the samples.（3）The sensitivity of the heat flow sensor was tested by comparison method.The results show that the average sensitivity of the sample with YSZ as the thermal resistance layer is 4.57×10^-4 m²·mV/W.The average sensitivity of heat flow sensor samples with SiO₂ as thermal resistance layer is 3.11×10^-4 m²·mV/W.The average sensitivity of the heat flow sensor sample with SiN as the thermal resistance layer is 4.01×10^-4 m²·mV/W,indicating that the thermal conductivity of the thermal resistance layer material will affect the sensitivity of the sensor.After the sensor experienced a high temperature thermal cycle of 1000℃under atmospheric atmosphere for 60 minutes,the average sensitivity of the heat flow sensor with SiN as the thermal resistance layer decreased to 3.54×10^-4m²·mV/W,less than 10%,indicating that the performance of the heat flow sensor with SiN as the thermal resistance layer was more stable after experiencing high temperature environment,and was more suitable for the measurement in high temperature environment.The thermal resistance layer with mesh cavity structure can significantly improve the sensitivity of heat flow sensor,and the sensitivity of heat flow sensor with SiO₂ mesh cavity structure as thermal resistance layer is increased by 60.54%.（4）The response time of the heat flow sensor samples is tested by a step wind tunnel with the air temperature of 500℃.The results show that the time constant of the sensors under the step wind tunnel reaches the order of 100 ms,which meets the requirement of fast response.（5）The thermal wind tunnel with temperature range of 200～500℃and airflow rate range of 0.2～1.0 Mach was used for environmental assessment of the heat flux sensor samples for 30 min.The results show that the output potential of the sensor has a linear relationship with the temperature change,the response is rapid,and the output is stable.