Simulation And Analysis Of High-voltage IGBT Switching Process Considering Distributed Gate Resistance Effect

Insulated Gate Bipolar Transistors(IGBT),as a high-voltage power semiconductor device,often operate under high-voltage and high-current conditions.In order to ensure that the device can work safely for a long time,the current and temperature inside the device chip should be distributed as evenly as possible,so it is necessary to study the law of current and temperature distribution inside the chip.Since most of the current semiconductor processes use doped polysilicon as the conductive layer to transmit the gate voltage driving signal,the distributed gate resistance effect formed by the polysilicon gate may cause signal transmission delay,such that the cells that are close to the metal gate pad or metal gate bus are turned on or off first,causing current concentration in the switching process of the device.For the solution of current concentration in switching process,it is common to design three types of gate bus,namely,the most dense design,the proper distribution design and the no finger design.Among them,the design principles of the former two have been explained by relevant literature,but the third type of no finger design is the most likely to induce current concentration,but it has not shown any disadvantage in practical applications,the intrinsic reasons are currently not explained in the detailed literature.Therefore,this paper will work on the current and temperature distribution of the IGBT chip in switching process,and explore the inherent reasons for the reasonable existence of the no finger design.Based on the Sentaurus-TCAD simulation tool,this paper focuses on the simulation study of current and temperature distribution in IGBT switching process.In order to simulate the actual situation of higher central temperature and lower ambient temperature when the chip is working,a two-dimensional model of parallel 4 cells with distributed gate resistance effect is established,and a temperature difference from left to right sides can be constructed when necessary,trying to reflect the current process of a large number of cells in the actual IGBT chip through the change of current and temperature distribution inside the 4-cell structure during the switching process.The results show that during the IGBT turn-off period,within a reasonable range of gate resistance,the distributed gate resistance effect causes the emitter current to appear uniform-uneven-reuniform evolution before the collector voltage rises.The current concentration phenomenon in the turn-off process occurs at a cell far from the gate drive source,and the magnitude of the gate resistance affects the timing and duration of current concentration.At the same time,the degree of current concentration during IGBT turn-off is also affected by the gate resistance and the distributed gate resistance.When the gate resistance is small,the current concentration is basically unchanged;when the gate resistance is large,the current concentration is weakened as the gate resistance increases.In a reasonable range of gate resistance,although the current concentration will cause the temperature in the area to rise,in the normal turnoff condition,the highest temperature rise due to current concentration is low,so the safe operation area of the device is not affected.The gate resistance has a large effect on the device turn-off rate.The larger the gate resistance,the slower the turn-off rate and the greater the turn-off loss.Since the heat dissipation rate in the center of the chip is slower than the edge when the device is continuously operated for a long time,a temperature distribution with a high central temperature and a low edge temperature is formed.After establishing a temperature difference between the left and right sides,the simulation shows that the overall temperature of the device will increase due to the turn-off loss in the turn-off process,but the temperature distribution at the center temperature is higher than the edge temperature is basically the same.On the other hand,the current concentration caused by the distributed gate resistance during the device turn-on process does not cause significant harm,but rather helps to drive the temperature distribution to be uniform.Corresponding this result to the gate bus design with no finger,it can be inferred that although the design method has the largest distributed gate resistance effect,current concentration is likely to occur during the switching process of the device,but the temperature gradient caused by current concentration will reverse when turned on,which in turn will facilitate the uniformity of the overall temperature of the device.In summary,this paper analyzed and discussed the current and temperature distribution of IGBT switching process by using simulation results combined with theoretical analysis,and explained the rationality of the no finger design that has been verified by practical application,and provided an important reference for the related research and development of IGBT.