Research On Preparation Technique For MEMS-based High Temperature Heat Flow Sensor

In the wind tunnel experiment,the high temperature environment will cause serious damage to the device.In order to ensure the reliability of the device operation and improve the working life of the device,the influence of the real working environment must be considered in the design process of the device.However,it is inaccurate to measure the severity of the working environment based only on temperature indicator.In order to describe the working environment accurately,the heat flow sensor which can characterize temperature gradient changes is needed.The volume of the heat flow sensor is an important factor that can affect the accuracy of the heat flow measurement.The big volume will interfere the actual propagation path of the heat flow,so that the measured data does not match the real situation.However,reducing the volume of the heat flow sensor will increase the difficulty of the preparation process,so the MEMS process is required to realize the preparation of the heat flow sensor with high sensitivity.According to the test requirements of wind tunnel experiments,the operating temperature of the sensor should not be lower than 450°C.In order to more accurately characterize the thermal environment and achieve the measurement of temperature and heat flow simultaneously,this paper mainly studied the preparation process of high temperature heat flow-temperature composite sensor.The work carried out throughout the research process included the following aspects:?1?The design of the heat flow sensor's overall structure was completed.Based on the working principle of the thermopile type heat flow sensor,in order to prepare a sensor whose working temperature is more than 450?and the sensitivity of heat flow measurement is more than 0.05?V/?W/m²?,the material and size of the substrate,the thermopile and the thermal resistance layer were sequentially determined.Then analyzed the parameters reasonably to confirm the feasibility of the design.?2?The preparation process of high temperature heat flow sensor was studied.The preparation of micro-scale thermopile and thermal resistance was mainly carried out by sputtering stripping process,and the influence of annealing process on the thermal resistance characteristics of thin film platinum resistor was investigated.It was found that the increase of the annealing temperature,the extension of the holding time and the increase of the substrate's roughness were all helpful to increase the sensitivity and linearity of the platinum resistance.When platinum resistance was deposited on an alumina substrate with a roughness of 40nm,the sensitivity was changed from 0.453?/°C to 0.521?/°C after annealing at 600?for 30minutes and increased by 15%,and the linearity was increased by 48%,from 13.5%to7.0%,an increase of 48%.Then,the preparation of the thermal resistance layer was completed by plasma enhanced chemical vapor deposition,and the local thinning of the thermal resistance layer was realized by the wet etching process.?3?Packaging and preliminary testing of the high temperature heat flow sensor were completed.The test mainly included three aspects,one is to measure the sensor's response time to the transient heat flow,the other is to evaluate the stability of the output voltage of the heat flow sensor under the same experimental conditions,and the third is to determine the impact between height difference of the thermal resistance layer and the number of sensor operations.The test data showed that the response time of heat flow sensor prepared in this paper was about4s.And the signal output under the same experimental conditions was very stable..The standard deviation of the output voltage was 2.469×10^-3 mV.It can be impacted by a high temperature heat flow of 810°C for 31 times.When investigating the influence of the height difference of the thermal resistance layer on the life of the sensor,it is found that the increase of the height difference can increase the number of thermal resistance layer operation,and the heat flow sensor whose thermal resistance layer height difference was 5.003?m could be washed by the heat flow of 497°C for 57 times.