The Research Of New Structure And Experiment Of Ultra-high Voltage SiC Power Devices

10 kV Ultra-high voltage（UHV）power devices are mainly applied to HVDC power transmission,all-electric ships,high-energy laser weapons and other fields.Si modules can achieve a 10 kV blocking capacity through series connection,which leads to a large number of components,a complicated system structure and many parasitic effects at the same time.The above-mentioned problems greatly restrict the performance of UHV power devices.Wide bandgap power semiconductor devices represented by silicon carbide（SiC）can significantly reduce the energy consumption of electronic equipments due to characteristics such as high breakdown voltage,low power loss,high thermal conductivity and so on,with great potential in the application field of ultra-high power electronics.SiC power device is known as the“green energy”device that drives the“new energy revolution”.The 10 kV silicon carbide device does not require complicated series-parallel structures,which helps to reduce the number of system components,simplify the circuit topology and improve the efficiency of power conversion and the reliability of systems.Up to now,10 kV UHV SiC power devices are still in the research stage.Therefore,the study of the new structure of UHV SiC power devices is of great significance in this dissertation.This dissertation aims at the key scientific and technical issues of the breakdown mechanism of the junction termination structure and the new structure of UHV SiC power devices.Researches of the charge field modulation,UHV SiC junction terminal models,a novel structure of Charge Field Modulated-JTE（CFM-JTE）for 10 kV SiC Pi N and a novel 10 kV SiC MOSFET embedding low barrier diode（LBD-MOSFET）are carried out.10 kV/100 A CFM-JTE SiC Pi N diodes and 10 kV/10 A SiC MOSFETs are fabricated based on domestic process conditions,which provides a theoretical basis and technical guidance for the design and development of domestic UHV SiC power devices.Main innovations of this dissertation are as follows:1.An analytical model of junction termination extension（JTE）structure for UHV SiC devices is established.The characteristics of the UHV SiC JTE structure are analyzed.The Sector Depletion Distribution-Junction Termination Extension（SDD-JTE）model and the Elliptical Depletion Distribution-Junction Termination Extension（EDD-JTE）model are established based on the charge field modulation mechanism and the theory of charge balance in the junction termination.The breakdown voltages of the junction termination extension structures can reach more than 98%of the theoretical breakdown voltage based on the SDD-JTE model and the EDD-JTE model,which achieves high voltage protection efficiency and good modulation effect of smooth distribution of the junction terminal electric field.The analytical values of the two models can provide a good foundation for the UHV SiC junction termination extension structure and the process design.2.A novel High-K dielectric Enhanced Depletion-Junction Termination Extension（HKED-JTE）structure and an Etching Uniform Field Limiting Ring（EU-FLR）are proposed for the 10 kV SiC power device based on the charge field modulation mechanism.HKED-JTE introduces a high-K dielectric layer on the surface of the JTE,which attracts the electric flux in SiC and optimizes the surface electric field distribution.In the blocking state,the high-K layer induces negative charges at the interface,which contributes to the enhancement of the JTE depletion.The peak electric field at interface between High K layer and SiC is reduced by 54%compared with Two Zone-JTE（TZ-JTE）structure.Thereby,HKED-JTE is able to widen the JTE dose tolerance window,reaching nearly 4 times that of the conventional TZ-JTE.EU-FLR optimizes the electric field distribution through changing the structural parameters such as etching depth,etching position and ring space.EU-FLR achieves a breakdown voltage of 90%of the theoretical breakdown voltage.With the same blocking capacity,EU-FLR reduces the junction terminal length by 30%compared to the traditional uniform FLR.With the same area as the traditional uniform FLR,the blocking capacity of the EU-FLR has increased by 58%.3.A novel structure of Charge Field Modulated-Junction Termination Extension（CFM-JTE）is proposed and the 10 kV/100 A CFM-JTE SiC Pi N diode is fabricated.The CFM-JTE structure introduces 5 regions with different charge amounts to modulate the electic field of the main junction and junction terminal of the UHV SiC Pi N diode.The breakdown voltage of the CFM-JTE structure reaches 99%of the theoretical breakdown voltage and the length is only 400μm.CFM-JTE has better process robustness and the implantation dose tolerance window is 7.1×10¹²cm^-2～1.35×10¹³cm^-2,which is 33%and106%higher than that of Outer Rings Assisted-JTE and Two Zone-JTE structures,respectively.The 10 kV/100 A CFM-JTE SiC Pi N rectifier is fabricated on a 100μm epitaxial layer of 5×10¹⁴cm^-3 and achieves considerable blocking capacity of 13.5 kV at the leakage current of 10μA,which obtains 96%of the theoretical breakdown voltage.The active area is 0.1 cm².The forward current density of the CFM-JTE SiC Pi N is measured up to 1000 A/cm² at room temperature.The Baliga’s figure of merit(BFOM=BV²/R_on,sp)reaches 173.6 GW/cm² and the related performances have reached the international advanced level.4.A novel 10 kV SiC MOSFET embedding low barrier diode（LBD-MOSFET）is proposed and the 10 kV/10 A UHV SiC MOSFET is fabricated.LBD-MOSFET forms a low barrier diode in the cell by introducing the N＿well region above the P＿base region on one side to reduce the electron barrier between source and drain.When the LBD-MOSFET works in the third quadrant,the low electron barrier enables the LBD to be turned on at a lower source-drain voltage,thus effectively avoiding the bipolar degradation effect caused by the turn-on of the body diode.The third quadrant turn-on voltage of the LBD-MOSFET is 1.3 V,which is 48%lower than the traditional structure.The specific gate-drain capacitance and high-frequency figure of merit(R_on×C_gd)of the LBD-MOSFET are 1.0 p F/cm² and 194 mΩ·p F,which are reduced by 81%and 76%compared with the traditional structure,respectively.A Central Surface Dielectric MOSFET（CSD-MOSFET）and a Central Buried Dielectric MOSFET（CBD-MOSFET）are proposed to improve the reliability of the gate oxide.The peak electric field in gate oxide of both CSD-MOSFET and CBD-MOSFET can be controlled within 2.5 MV/cm,which is 30%lower than that of the traditional structure.The 10 kV/10 A SiC MOSFET is fabricated on a 100μm epitaxial layer of 5×10¹⁴cm^-3 and achieves the breakdown voltage of 11.3 kV at the leakage current of 10μA.The active area is 0.3 cm².The threshold voltage is 6.4 V@J_DS=0.5 A/cm²,V_DS=1 V.The device obtains a forward current of 10 A@V_GS=18 V,V_DS=5 V and a specific-on resistance of 130 mΩ·cm²@V_GS=18 V.The Baliga’s figure of merit(BFOM=BV²/R_on,sp)reaches 0.98 GW/cm² and the related performances have reached the international advanced level.