Research On A 4H-SIC Based MIS SBD High Temperature Gas Sensor

With the rapid development of science and technology,the fields of defense military,automotive electronics,aerospace,industrial electrical automation,fuel cell and other fields are increasingly requiring the development of high-temperature gas sensors to promote technological innovation.However,silicon-based devices mostly used in low-temperature and low-frequency conditions,and they can't applied to high temperature environment.Therefore,researchs on high-temperature gas sensors based on silicon carbide have become a hot topic,especially the metal-insulator-semiconductor Schottky diode(MISBD)sensor which has become the focus of research because of its simple structure,easy fabrication,and easy integration.But in previous studies,researchers mostly used oxide as the insulating layer of sic based high temperature gas sensor.This kind of insulationglayer has a low thermal conductivity,has a serious mismatch between substrate lattice and itself,and cannot withstand a higher temperature environment,resulting in lower sensor reliability and limited application range.In this paper,the high temperature hydrogen sensor which uses aluminum nitride as insulating layer and uses 4H-SiC as based is deigned.It solves the serious mismatch between the insulating layer and the semiconductor lattice,and improves the sensor's sensitivity and reliability in high temperature conditions.This paper mainly studies the sensor sensitivity mechanism,simulates and analyzes the sensor sensitivity and high temperature characteristics,optimizes the sensor structure,designs the sensor process and carries out some experimental researches.The specific contents of the researches are as follows:(1)Analyzing the sensing principle of the sensor,and then explore the role of the material of each layer of the sensor,ensure the selected material of each layer and establish the structure of the sensor,including 4H-SiC substrate,4H-SiC epitaxial layer,AlN insulating layer,the front and back buffer layers,the front and back electrodes.(2)Establish the simulation model of the sensor(including the sensor structure and the application of physical model).Considering the sensor structure and the accuracy and rapidity of simulation calculation,the buffer layer of adhesion is omitted,and the substrate is simplified to 1um thickness,and the front.electrode is simplified to contact with the semiconductor Schottky,and the back electrode is simplified to contact with ohmic.The applied physical models mainly include semiconductor basic equations,mobility models,band width narrowing models,Auger recombination and Shockley-read-hall recombination models,tunneling models,and so on(3)The effects of temperature,hydrogen concentration and thickness of insulating layer on I-V output characteristics of sensor are studied and analyzed,and then,the sensor current resolution and sensitivity curve are analyzed to determine the optimal insulating layer thickness of the sensor.The results shown that when the temperature is less than 573K,the output current rises with the rise of temperature,which due to the action of the catalytic metal,the number of hydrogen atoms which form the polarization layer increase,then the barrier height becomes smaller.When the temperature is between 573K and 773K,the output current decreases with increasing temperature.This is because as the temperature increases,a part of hydrogen atoms combine with oxygen atoms to form water,and the barrier height becomes large.When the hydrogen concentration increases and the height of the barrier is lower than before,the current of the sensor consequently increases.As the thickness of the insulating layer increases,the number of electrons passing through the insulating layer is reduced,causing a decrease in the output current of the sensor.The results shows that a thicker insulating layer thickness can decrease the current resolution and increase the sensitivity of the sensors.According to the condition that when the sensor is applied under high temperature,the current resolution should be greater than 1 mA,and the current sensitivity is greater than 40%,and the optimal insulating layer thickness is determined to be 1.45-2.32 nm.Finally,2nm is selected as the thickness of the sensor's insulating layer.Next,we simulated and analyzed the change of output current with the hydrogen concentration at a temperature of 573K.It is proved that the sensor has good current resolution when the hydrogen concentration is less than 200ppm,and has good linearity when the hydrogen concentration is greater than 200ppm.(4)The experimental procedure was designed to focus on the experimental conditions of pulsed laser deposition(PLD)aluminum nitride,and an aluminum nitride film with good crystal orientation and good surface quality was prepared.In summary,the MISiC SBD high temperature hydrogen sensor with aluminum nitride as insulating layer is simulated in this paper.The structure of the sensor is designed and optimized,the I-V characteristics of the sensor are simulated and analyzed,and the insulating layer of the sensor is determined.The simulation results shown that the optimal thickness of the sensor's insulating layer is 1.45-2.32nm.When the thickness of the insulating layer is 2nm,the current resolution is 1.26mA,the sensitivity is 54%.When the hydrogen concentration is less than 200ppm,the current resolution is good.When the concentration is greater than 200ppm,the linearity of the sensor is better.The experimental results shown that at a pulse frequency of 5 Hz,a laser energy density of 3 J/cm~2 and a target base distance of 50 mm,an aluminum nitride film having a crystal orientation can be(111),a grain size is 26.6 nm,and a surface roughness is 1.163 nm can be prepared.