Structural Design And Characteristic Research Of High-power 4H-SiC GTO Device

With the continuous progress of rail transit,electric vehicles,pulse power technology,ultra-high voltage direct current transmission and other technologies,the demand for high-power semiconductor switching devices is very urgent.Relying on the development of the third generation of wide-bandgap semiconductor materials,the silicon carbide gate turn-off thyristor(SiC GTO)breaks severe system limitations due to the Si thyristors in blocking voltage,switching speed,working temperature and power density and so on.With the double-side carrier injection and conductivity modulation effect,SiC GTO devices can handle large blocking voltage and high conduction current at the same time.They can reliably switch on and off for several thousand times with extremely high value of di/dt under high temperature.Therefore,the SiC GTO has become a kind of promising power switching device with the large demand and wide application in the fields of inverters and high-power pulse military equipment.In this paper,a 10 kV SiC GTO device is designed,and the work is carried out from five perspectives including mechanism modeling,parameter optimization,structural design,characteristic research and device fabrication.The main contents are as follows:(1)By figuring out the material mechanism and operating principle of the device,the physical models of silicon carbide based on Silvaco TCAD are established.(2)Considering forward blocking characteristic,forward conduction characteristic and turn-on delay time,the basic structural parameters of the device are optimized by simulation.Based on the single-zone junction termination extension technology,the etched junction termination extension with rings is proposed and optimized.Its junction termination efficiency is up to 97.4%.When the efficiency is above 85%,the injection dose of JTE zones can range from 6.9e12 cm^-2 to 15.2e12 cm^-2.(3)The simulation is conducted with the well-designed and optimized structure.The temperature characteristic,switching-on characteristic,switching-off characteristic and pulse discharge characteristic of this device are studied in detail.The SiC GTO device with forward voltage drop of 4.605V(@1000A/cm²)is obtained.The blocking voltage of cell is 14.78 kV,and its blocking voltage with the proposed junction termination technology is 14.4 kV.According to the double pulse test circuit,its turn-on time is 55 ns and the turn-off time is 13.3?s.According to the capacitive pulse discharge circuit,its turn-on delay time is 110 ns.With pulse width of 0.8?s,the maximum voltage drop is 75V under the peak current value up to 7035 A(62.5 k A/cm²),and the corresponding current rise rate is 40 k A/?s.(4)In order to enhance the conductivity modulation effect,a grooved SiC GTO device is proposed.Its forward current density is higher than the counterpart of the conventional one,and the current improvement is 10%at 5 V.In the same pulse discharge circuit,its maximum voltage drop can be reduced by 20%compared with the conventional GTO device.(5)In order to prove the effect of the grooved anode on current,SiC PiN devices with grooves are manufactured.The tested forward current of the sample is 71.5 A@4 V with the chip area of 5.6×5.6 mm².Compared with the conventional PiN structure,the current improvement of 32.5%@4 V is achieved.