Research On Monolithically Integrated Smart Power Devices Based On 4H-SiC Bipolar Technology

Owing to the continuously growing requirements for power electronics systems and their expansion into new fields,there is a strong demand for the power electronic systems that can endure higher temperature(>300?)and possess stronger reliability and robustness in some applications,such as aerospace,deep earth oil drilling,clean energy and national security defense.Power devices are facing the same challenges as the key component of power electronic systems.However,only high performance power devices are far from enough because the entire power electronic system cannot work in harsh environment if the drive circuit is still silicon-based.Therefore,it is necessary to design high performance SiC integrated circuits to drive and control the SiC power devices.By integrating functional integrated circuits onto the power devices,power ICs can effectively reduce circuit stray inductances,increase and enhance the functions of power devices,thereby it is a key technology to promote power electronic systems to achieve energy saving,higher efficiency,miniaturization,lighter weight and higher reliability and robustness.So far,SiC power ICs have been simply realized by packaging the discrete devices and some analog or logic circuits,but a higher-level monolithic SiC power ICs is still in the preliminary stage of exploration.In order to meet the future demand for SiC power electronics systems that can endure higher temperature and possess higher reliability and higher efficiency with smaller size,this thesis has carried out preliminary explorations on the key technologies of monolithic integrated smart power devices based on SiC bipolar technology,including(1)Design of monolithically integrated smart SiC power device structure,(2)Design and verification of new isolation structure for SiC power ICs,(3)Compatible processing for SiC power ICs,(4)SiC devices library models establishment and their applications.Innovations in this thesis are summarized as following.(1)This thesis proposes a new structure for SiC power ICs based on SiC bipolar technology.Based on the epi structure of SiC power BJT,a SiC LBJT and a SiC BJT/diode integrated structure that are suitable for monolithic integration are proposed to provide a solution for the SiC power ICs.The static characteristics and switching characteristic under back-gating effect are studied by TCAD simulations and experiments.The results reveal the feasibility of the new SiC LBJT for the development of SiC power IC.Considering that power switch usually requires an anti-parallel diode as freewheeling,this thesis also proposes a method to introduce an isolation ring between the borders of the devices to relieve the electric field crowding effect so that the breakdown voltage degradation problem can be solved in SiC integrated devices.Some integrated SiC BJT/JBS research samples with breakdown voltage higher than 1200V have been successfully developed,which not only verifies the simplicity and effectiveness of the idea but also demonstrates the feasibility of the integrated SiC BJT/JBS new structure.This research paves the way for subsequent design of SiC power IC.(2)This thesis proposes a combined isolation scheme of"shallow trench isolation+self isolation+semi-insulating layer isolation",and studys the method of using vanadium ion implantation in SiC to selectively form a semi-insulating structure.Vanadium ions will replace Si sites after doped into SiC,and they could have three possible charge states as V_Si³⁺,V_Si⁴⁺and V_Si⁵⁺.Therefore,they may act as deep-level donor and/or deep-level acceptor in SiC and make the SiC substrate and epilayer restore to semi-insulating layer by compensation effect.With this theoretical guidance,the specific on-resistance of a SiC epilayer has been successfully increased from 10.8m?·cm² to 1.92×10⁶?·cm²(i.e.,1.8×10⁸X)through further experimental research in this thesis.Therefore,it is experimently proved that the vanadium ion implantation is capable of selectively forming semi-insulating layer in SiC to serve as isolation structure,which will strongly promote the development of SiC power ICs.(3)This thesis studies the fabrication process of SiC power ICs.Based on the analysis of the differences between the fabrication processes of power devices and integrated circuits,a set of highly compatible fabrication processing is designed.Taking SiC power BJT and small-signal SiC LBJT as examples,the compatible fabrication processing has been successfully used to simultaneously fabricate SiC power BJT and small-signal SiC LBJT on the same epitaxial wafer in this thesis.The SiC power BJT and SiC LBJT show relatively good device characterisitics,demonstrating the feasibility of the compatible fabrication processes.Above all,this research provides a set of fabrication process for the SiC PIC based on SiC bipolar technology.(4)This thesis also proposes a new SPICE model that can accurately predict SiC BJT's behaviors in both wide temperature and wide current ranges.It is found that ignoring the surface recombination effect caused by the poor SiC/SiO₂ interface is an important factor affecting the accuracy of SiC BJT modeling.This thesis proposes to use a diode with an ideality factor of about 2 to characterize the surface recombination effect after analyzing SiC/SiO₂ interface with SRH recombination theory,which solves the difficult problem of modeling surface recombination effect.On this basis,new SRGP models have been developed for both SiC power BJT and SiC LBJT to accurately predict their characteristics in a wide current and wide temperature range.The model is then used to design some analog or logic circuits such as NOR,differential amplifier circuits and push-pull drive circuits to verify its feasibility in the design of functional ICs.This research will provide a useful device library model for the design of functional integrated circuits in SiC Power ICs.All the research work in this thesis is dedicated to promoting the development of SiC power ICs,providing possible solutions and necessary technical preparations for solving key scientific and technological problems in high performance power electronic systems.The development and application of SiC power ICs is expected to improve the performance of power electronic systems and promote the development of aerospace,deep earth oil drilling,clean energy and national security defense.