Analysis And Optimization Of Turn-off Robustness On U-shaped Channel Soi-ligbts

Single-chip smart power chips are widely used in various motor driving and power applications due to their low loss and small size.Silicon on Insulator Lateral Insulated Gate Bipolar Transistors?SOI-LIGBTs?are the core switching device in single-chip intelligent power chips.These devices have strong current capability,high breakdown voltage and integrate easily.At the same time,the maximum current that can be normally turned off at rated voltage is determines by the turn-off robustness of such devices.It is important to study and design SOI-LIGBTs with stronger turn-off robustness for chip's reliability.Based on the U-shaped channel SOI–LIGBT device structure proposed by the research group,this thesis tests and evaluates the range of its turn-off robustness,and finds that the turn-off failure current of single-runway device and multi-runway device is far lower than the value designed and proportional to the number of runways.In this thesis,the device turn-off process is reprodueced and the failure mechanism is studied.It is found that the U-shaped channel device will avalanche at the beak near the emitter at the beginning of the turn-off process,then a large amount of holes and electrons are produced.Under the influence of the electric field,large of electrons are transferred to the vicinity of the collector,causing the parasitic PNP transistor turning on.Then the device fails due to excessive current by avalanche breakdown.In summary,two improvements are proposed in this thesis.The first method is shifting the position of the peak electric field and the peak current,and the second method is reducing the injection efficiency of the parasitic PNP transistor.Finally,a comprehensive optimization structure is obtained.Simulation results of the new structure reveal that the critical turn-off failure current of the U-shaped channel is raised from 450V,1A to 450V,2.47A,an increase of 147%.At the same time,the breakdown voltage of the device is maintained at 560V,and the current density is maintained at 307 A/cm²(V_CE=3V).