The Optimization Design Of Structure For Ultra-High Voltage 4H-SiC GTO Thyristor

Although the Si thyristor has been successfully used for many years, its blocking voltage and dv/dt, di/dt capability have been gradually approaching the physical limits of the Si material, and rely on the optimization of structure design and manufacture process of Si thyristor to further improve the potential of single Si thyristor are limited. With the development of silicon carbide (SiC) materials, using SiC materials instead of conventional Si materials has attracted more and more attention. Therefore, in this paper, taking 20kV SiC gate turn-off thyristor (GTO) for example to carry out an ultra-high voltage structure design and optimization by a method of software simulation. Meanwhile, the turn-on mechanism of the SiC p-GTO thyristor device, the effects of temperature and lifetime on the device performance are studied. The main research contents and conclusions are as follows:1. The design and optimization of 20kV SiC GTO thyristors are carried out. The p-n-p-p-n device structure with p blocking base layer is selected, and doping concentration and thickness of p blocking base layer are 2×1014cm-3 and 160 μm, respectively. To obtain a lower voltage drop, insert a buffer layer between the lightly doped p base layer and heavily doped n+substrate, as a result, the device structure is not punch-through. The optimal doping level and thickness of other epilayers are: p+ emitter layer(5×1019cm-3, 3.0 μm), n base layer(2×1017cm-3,5 μm) and n+ substrate(2×1019cm-3, 50μm). It is worth mentioning that the lateral length of emitter layer is 30 u m by optimization.2. The turn-on process of SiC GTO thyristor has been studied. In the turn-on process of SiC GTO thyristor,the delay time and extend time are all in nanosecond level, which is different from the figure that extend time is far greater than the delay time in Si GTO thyristor.And propagation velocity of UHV 4H-SiC GTO thyristor is about 1.64×104cm/s, while the max propagation velocity rate of Si thyristor is 1×104cm/s, thus SiC thyristor is about 1.64 times far greater than the propagation velocity rate of Si thyristor. The expansion phase of the SiC GTO thyristor is extended under the action of both drift and diffusion.3.The influence of temperature and lifetime on the characteristics of SiC GTO thyristor is completed. With the temperature increases, the forward blocking voltage of SiC GTO thyristor decreases slightly and leakage current increases evidently. Under the high temperature of 600K,SiC GTO thyristor is still in the forward blocking mode, no self-triggering phenomenon. As temperature increases from 300K to 500K, the on-state voltage at anode current of 100A/cm2 declined about 0.42V. And, temperature increases from 300K to 500K, the turn-on time is reduced about 38ns, the turn-off time increases about 78ns; At room temperature, for the 20kV SiC GTO thyristor, to obtain a lower forward voltage drop, lifetime of p drift layer is not less than 5μs.