Study On Longitudinal Heat Conduction By AlN Film And Dual Coordinate Self-Examined Microarray Airflow Sensor

Airflow sensors are widely used in industrial,agricultural production,space sounding,micro weather stations,human life,transportation,transportation,pipeline transportation and meteorological monitoring fields.It is an important tool for obtaining the size and direction parameters of airflow.Among many airflow sensors,MEMS airflow sensor has important research value because of its small size,light weight,simple principle,easy to integrate and not easy to wear.Calorimetric airflow sensor is a typical airflow sensor,and the working principle of the calorimetric airflow sensor is realized by heat exchange between the heating element of the sensor and the external environment fluid.The heating element provides a stable and balanced temperature field distribution for the temperature sensitive unit.When there is no air flow,the output of the sensor is zero.When air flow passes,the equilibrium temperature field is broken,and the sensor has corresponding output of voltage / current.According to the size of output signal,flow velocity and flow direction of air flow are determined.Heat transfer mode of heat flow sensor is different due to different structures.And MEMS calorimetric sensor is the trend of its development.At present,the MEMS calorimetric gas flow sensor mainly has the problems of micro structure measurement blind area,low heat conduction efficiency and unable to self-test when there is no external additional modules.So it can not meet the needs of high precision measurement in the specific application.This paper focuses on the research of several key technologies,such as MEMS heat flow sensor model structure,heat transfer mode,high thermal conductivity and good insulation heat conduction film,the dual coordinate self checking algorithm and so on.In the design of airflow sensor structure.ANSYS 3D simulation software is used to simulate and analyze the shape and quantity of the heating unit and the thermal isolation structure.Considering the problems of high temperature of the sensor and low temperature of the temperature sensitive unit,regular octagon and circle heating coil structure are designed respectively.Under the condition of guaranteeing the same power consumption,the number of heating units is set to 1,2 and 4.Obtain the optimal structure,according to the temperature field distribution results of different shapes and numbers.In view of the high heat loss of calorimetric airflow sensor,four thermal isolation structure models are designed.The simulation results of temperature field of the four structures are compared with each other to determine the optimal thermal isolation structure.In the analysis of heat conduction mode of airflow sensor.In view of "transverse" heat conduction of airflow sensor,it shows that it is contradictory to speed the heat transfer efficiency and decrease the heat loss of the sensor,and to improve the temperature of sensitive unit and slow down the aging speed of the sensor.So the "longitudinal" heat conduction mode airflow sensor is designed.The heat conduction mode has the advantages of accelerating the heat transfer efficiency,reducing the heat dissipation,slowing down the aging speed of the device and reducing the heating power.In the study of single a-axis preferred orientation Al N insulation thermal conductive film.In order to improve the heat transfer efficiency of calorimetric airflow sensor,and to realize the electrical insulation of heating unit and temperature sensitive unit,the insulating heat conduction single a-axis Al N thin film is used.Compared with other orientation Al N films,single a-axis Al N films are more difficult to be prepared.Single a-axis oriented Al N film was prepared by RF sputtering for the first time.By changing the RF sputtering power,such as sputtering pressure,annealing temperature and many other factors,the crystal orientation,grain size,surface roughness and other parameters,to determine the optimized sputtering parameters of the Al N film.In the study of the double coordinate self-checking algorithm of the airflow sensor.At present,the designed calorimetric airflow sensor can not be tested by itself,or it can realize the self-checking function of the sensor by connecting with the external circuit or instrument.This self-examination method is very complicated and difficult to operate.Therefore,the layout of dual coordinates "?" type temperature sensitive cell is proposed.The layout of the sensitive units can improve the measuring range of sensors and reduce the blind area of measurement.Moreover,the flow velocity and flow direction are calculated by the voltage output of 8 temperature sensitive units,and the self inspection function of the air flow sensor is realized without external additional modules,according to the constant relationship between flow velocity and flow direction.The results show that when the shape of heating unit is regular octagon and the number of heating units is 2,the highest temperature in a temperature field is lower and the temperature of sensitive unit is higher.The thermal isolation structure of the sensor is beneficial to improve the temperature field distribution of the air-flow sensor,and provides a theoretical basis for the design of the sensor.The heat transfer mode of "longitudinal" heat conduction mode is beneficial to speed up the heat transfer efficiency,reduce heat dissipation,slow down the aging degree of the device and reduce the heating power.The single a-axis oriented Al N thin film is used to realize the longitudinal heat conduction mode of the sensor and effectively realize the electrical insulation between the heating unit and the sensitive unit.The dual coordinate self-checking algorithm is used to detect the flow velocity and flow direction of the air flow sensor,and the self inspection function of the air flow sensor is realized without the external additional module.