Study On High Temperature Characteristics And Modleing Of N-Channel 4H-SiC MOSFET

Compared with Si integrated circuits,SiC integrated circuits have the advantages of wider temperature range,higher voltage and greater radiation immunity,which can work in a variety of harsh environments,widely used in aerospace,oil and gas,nuclear and chemical industries.The output and transfer characteristics of the SiC MOSFET devices at high temperature change compared to that at room temperature due to the high interface state density.So,the traditional Si MOSFET device model is not suitable.Therefore,it is of great practical significance to study the high temperature characteristics of SiC MOSFET devices and establish corresponding models to give full play to the application of SiC MOSFET devices in high temperature integrated circuits.In this thesis,the high temperature characteristics of n-channel lateral 4H-SiC MOSFET devices with ion implantation are tested and modeled.A set of modeling methods for the high temperature model in Sentaurus TCAD and Matlab/Simulink are presented,which provide the basis for the design and application of SiC MOSFET in high temperature resistant integrated circuits.The main work and conclusions are as follows:(1)The basic structure of the device is first introduced in this paper.On this basis,the high temperature test platform based on Agilent B1505A semiconductor analyzer is used to test the static characteristics of the n-channel SiC MOSFET produced by the laboratory at different temperatures,mainly with output and transfer characteristics.The threshold voltage and mobility at different temperatures are extracted by the transfer characteristic curve.It is found that the operating current increases,the mobility increases and the threshold voltage decreases with the temperature rise.On this platform,the monitoring capacitance was tested with high frequency to extract the basic parameters of the gate oxide layer.Then the parameters of ion injection in each region of the device are calculated by SRIM software simulation according to the process parameters,which lays a foundation for device modeling.(2)Secondly,the relationship between the scattering mechanism and temperature of SiC MOSFET is discussed by consulting literature,in which lattice scattering and temperature are positively correlated,while ionized impurity scattering and temperature are negatively correlated.The surface roughness scattering is independent of temperature while the surface phonon scattering increases with temperature rise as well as the interfacial coulomb scattering.Then the basic model and mobility model and its related parameters in Sentaurus TCAD are introduced.Among them,the oxide layer fixed charge density of n-type and p-type MOS capacitance were extracted by high frequency CV test respectively.It is found that the difference between the two extraction results is quite large,which indicates that the influence of the process must be taken into account when modeling.Due to the device substrate is p-type,thus we adopting the p-type MOS extraction result for simulation.Then the interface state density at different temperatures were extracted according to the Terman method to determine the order of magnitude of the interface state density and the trend with temperature.(3)A model corresponding to the test results is established by adjusting the rough scattering parameters and the trap parameters of the interface.It is found that if the interface trap parameters at room temperature are used to simulate the device at high temperature,it will deviate greatly from the test results.Finally,by adjusting the peak concentration of the interface trap,the simulation model at high temperature is successfully established,which shows that the decrease of the interface trap leads to the increase of the mobility,the decrease of the threshold voltage and the increase of the working current.(4)The influence of different substrate concentration,different gate oxide layer thickness and self-heating effect on the high temperature characteristics of the device is analyzed and discussed according to the established Sentaurus TCAD model,and the characteristics of the resistive-loaded inverter circuit are simulated according to the model.From the simulation,it is found that inverter can be reversed in the temperature range from room temperature to 200 ? by selecting the appropriate load value.Although the SiC circuit is relatively stable at a separate temperature,its characteristics change with temperature which requires special attention in the design and application of high temperature integrated circuits.(5)In order to carry out the circuit simulation better in the future,by improving the basic model of Si MOSFET,the model of SiC MOSFET is established in Matlab/Simulink,and a simple modeling method is given.The fitting degree of the simulation and the test results are very well.With self-contained component library,the model can be applied to the high temperature circuit simulation.