Research On Avalanche Effect And Its Destruction Mechanism In IGBT And IGCT

The insulated gate bipolar transistor(IGBT)and the integrated gate commutated thyristor(IGCT)are currently two power devices with excellent performance and wide application.With the increase of device voltage level and current capacity,the avalanche effect has become an important factor limiting the safe operating area(SOA)of the devices.When the avalanche effect occurs in IGBT and IGCT,the hole injection of the p+n junction on backside of both has an important impact on the avalanche effect.In this paper,by theoretical analysis,analytical modeling and numerical simulation,the static avalanche robustness of the two devices under over-voltage and the dynamic avalanche robustness during the turn-off are studied,and combined with the measurements,the failure mechanisms of the two devices in practical applications are also explored.The main research results are as follows:Firstly,when IGBT and IGCT work in the static avalanche mode,the turning point current of the positive and negative differential resistance branches in the static avalanche breakdown curve of the devices dominates the strength of the avalanche-generated current filament,and the offset of the avalanche breakdown curve caused by temperature rise dominates the moving velocity of the filament.The larger the ?pnp of the devices is,the stronger the strength of the filament is and the slower the moving velocity of the filament is,which can weaken the static avalanche robustness of the devices.Secondly,when IGBT and IGCT work in the dynamic avalanche mode,the hole injection from the backside of the devices will enhance the dynamic avalanche effect,causing the avalanche-generated current filament to have a feature of vertically penetrating the devices.The larger the ?pnp of the devices is,the slower the moving velocity of the filament is,which can weaken the dynamic avalanche robustness of the devices.Thirdly,the analytical model for the dynamic avalanche onset voltage of IGBT is derived.The analytical results show that the dynamic avalanche onset voltage not only depends on the doping concentration of the N' drift region,but is also affected by the free carriers through the space charge region;the dynamic avalanche onset voltage decreases with the increase of the?pnp of the device and the turn-off current.The analytical model for the voltage rise phase during the turn-off of IGCT is derived,which can characterize the change of the device terminal voltage,the width of the space charge region and the internal electron current density over time.Fourthly,the dynamic avalanche effect and the current filament during the turn-off of IGCT can cause strong current crowding into the outer rings,leading to the device destruction due to the re-triggering in the outer rings.The voltage-clamping can occur when the IGBT is turned off under over-stress conditions.At that point,the current filament that moves slowly can cause the device failure due to local overheating,and decreasing the ?pnp of the device can improve the robustness of the device under this operating condition.Lastly,a voltage self-clamping mechanism is discovered during the over-stress turn-off of IGBT and IGCT,which is induced by strong dynamic avalanche injection and is destructive to the devices;the derived analytical model shows that the clamping voltage depends on the ?pnp of the devices and the turn-off current.