High-precision Spice Model Of SiC MOSFET For High-temperature Integrated Circuits Application

The superior properties of silicon carbide,such as high thermal conductivity and wide band gap,make it possible to work reliably for several hours in a high temperature environment,and it is widely used in the field of power electronics.Among all SiC-based devices,SiC MOSFETs are widely used due to their small tail current,low on-resistance,fast turn-on and turn-off transition speed,nearly insulating gate electrode,and high temperature resistance.At present,SiC MOSFETs have been widely used in important fields such as thermal power generation,oil exploration,and space exploration.However,being in a high temperature environment for a long time will affect the characteristics of the device,and even cause the degradation of the gate dielectric.In order to make SiC materials better used in the design of high-temperature integrated circuits,it is necessary to design a high-precision Spice model applied to SiC MOSFETs in high-temperature integrated circuits.In this thesis,the DC characteristics,C-V characteristics and high temperature behavior of planar lateral 4H-SiC MOSFET devices are experimentally tested and the corresponding intensive model studies are carried out.Based on the BSIM4.8 model implemented by Verilog-A,considering the influence of the interface state,a high-temperature model with high precision that can reflect the DC and CV characteristics of SiC MOSFETs and the corresponding model parameter extraction and optimization methods are respectively given.It provides an indispensable theoretical basis for further research and exploration of SiC MOSFET high temperature resistant integrated circuits.The main contents of this thesis are as follows:（1）In this thesis,the theoretical basis for modeling is given first.The significant advantages of SiC materials working in high temperature environments are introduced,and the research history of SiC MOSFETs,high temperature-resistant integrated circuits and their models at home and abroad is briefly listed.It is found that there is a lack of research on lateral 4H-SiC MOSFET devices and models.The structure,principle and important parameters of lateral 4H-SiC MOSFET are summarized,and the experimental test platform and topology circuit are briefly introduced.Outline the advantages and disadvantages of the three commonly used Spice intensive models.In order to comprehensively consider the accuracy and complexity of this modeling,this thesis adopts the standard intensive model realized by Verilog-A—the BSIM4 model based on threshold voltage as the basic model for correction.（2）The DC characteristics of SiC MOSFETs are greatly affected by temperature,so this thesis will focus on the establishment of the DC model of the device.Firstly,the BSIM4.8model built in Keysight ICCAP is used for simulation.The results show that the BSIM4.8model is not enough to accurately simulate the output characteristics and transfer characteristics of the device.The main reason for the huge difference in the characteristics of SiC MOSFETs and Si MOSFETs is the large SiC/Si O₂ interface roughness and interface state density.Therefore,this thesis analyzes the influence of interface states on device characteristics with the help of the energy band diagram working in the accumulation region and inversion region.The results show that it will cause the decrease of device mobility,the increase of subthreshold slope,the change of bulk effect,soft saturation and high temperature behavior changes.On this basis,this thesis modifies the BSIM4.8 model formula and model parameters related to the interface states,and then proposes a new model parameter extraction and optimization sequence.The accuracy of the model is verified by using the planar lateral 4H-SiC MOSFET tape-out in the laboratory as a reference device.By simulating the DC characteristics of the device in the temperature range of 25°C to200°C,the results show that the model simulation and actual test results are in good agreement,which verifies the accuracy of the high-temperature DC model of the SiC MOSFET.（3）The C-V characteristics of SiC MOSFETs directly affect the switching speed and operating frequency of the device,so it is also crucial to establish an accurate high-temperature C-V model.Firstly,the BSIM4.8 small-signal capacitance model and its simulation results are presented.The results show that the BSIM4.8 model is not enough to describe the C-V characteristics of SiC MOSFETs under the influence of interface states.The effect of the interface state on the CV characteristics of the device is also analyzed by means of the energy band diagram.The results show that the interface state not only causes the shift of the threshold voltage and the flat-band voltage in the CV characteristics,but also makes it affected by the frequency.The BSIM4.8 model does not describe this physical effect.In order to avoid problems such as complexity and non-convergence,this thesis does not directly modify the charge formula,but chooses to modify the threshold voltage and flat-band voltage models in BSIM4.8 from the impact results,and gives the new model parameter extraction and optimization sequence in detail.The C-V characteristics of the revised model are simulated and verified in the temperature range of 25℃～200℃,and the accuracy of the model is high.In order to verify the guiding significance of the model in the design of high temperature resistant integrated circuits,this thesis builds a common source amplifier and a pseudo NMOS inverter for verification.（4）Different sizes of 4H-SiC N-type and P-type MOSFET devices and high-temperature integrated circuits are designed,and the device size that can match current is given based on theoretical knowledge.A set of process flow for saving reticle and realizing simpler device fabrication is proposed.The layout is designed and tape-out in L-edit,which provides experimental basis for the development of high temperature resistant integrated circuits.