Study On Dynamic Avalanche Characteristic Of SOI-LIGBT

Silicon-On-Insulator Lateral Gate Bipolar Transistor(SOI-LIGBT)is the core switching device in a single-chip intelligent power chip because of its high breakdown voltage,high current capability and easy integration.In practical applications,dynamic avalanche of SOI-LIGBT will be caused by high voltage and high current,and the capability of dynamic avalanche is one of the key factors that determine the robustness of devices.Thus,it is necessary to study and optimize the dynamic avalanche characteristic of SOI-LIGBT devices.Based on the SOI-LIGBT developed by our lab,the dynamic avalanche characteristic of the device under clamped inductive load,short circuit and unclamped inductive switching(UIS)is deeply studied.It is found that:dynamic avalanche occurs in the emitter region of the device during clamped inductive switching,and then current accumulation and local temperature are rised because of a large number of electrons and holes,which lead to the parasitic NPN transistor turning on and device failure.At the beginning of short circuit,the electrons generated by the dynamic avalanche at the emitter side move to collector side,and make impact ionization increase.The holes flow back to the emitter due to impact ionization in the collector region,causing the parasitic NPN transistor turning on and the device failure.As the short circuit continues,the lattice temperature increases,and the maximum impact ionization position in the device transfers from emitter side to collector side,resulting in overheating failure.During the process of unclamped inductive switching,the energy stored in the inductance is released through the device,resulting in the collector voltage rapidly exceeding the avalanche breakdown voltage.The device failure would occur with weak dynamic avalanche capability.Based on the above mechanism analysis,the factors of internal parameters and external parameters are studied.In this thesis,two solutions are proposed:the emitter side conductive trench is introduced to adjust the current path;the distance between the beak and emitter is increased to shifting the position of the peak electric field and the peak current.Simulation results of the new structure reveal that the avalanche current is 248.45A/cm~2,and the avalanche resistance is1.7J/cm~2,which is 70%higher than the traditional structure.