Research Of Short-Circuit Turn-off Capability And Key Technologies Of IGBTs

As the most developed power semiconductor device,IGBT?Insulated Gate Bipolar Transistor?has been widely used in rail transit,smart grid and other fields due to its easy gate drive and high current density.Hence,it is regarded as the CPU of power converters.Load short circuit is a circuit fault that IGBT occasionally confronts in applications.In order to avoid damage to the device caused by short-circuit fault,IGBT is required to withstand the short-circuit stress during the response time of the protection circuit.The short-circuit capability of the device has become an important parameter of application reliability of IGBTs.Major IGBT manufacturers in the world have launched relevant research and products.But the work of studying IGBT short-circuit turn-off capability of domestic IGBT manufacturers has not been systematic.Furthermore,there are few product reports that the short-circuit capability is regarded as a consideration of device trade-off design.Based on this,two high-voltage IGBT structures that enhance the short-circuit capability of the device from the control of the hole and electron path are illustrated in this work,which provides a new design methode for improving the short-circuit capability of the IGBT device.In order to control the hole path of IGBT during short-circuit,an device structure with Adjustbale Hole Path?AHP?is proposed.The AHP region controlled by the JFET structure is proposed to achieve hole storage during normal conduction,maintaining a low on-state voltage.Meanwhile,AHP region provides an additional hole path during turn-off,reducing turn-off time and turn-off loss by 19.6%and 30%,respectively.In the blocking state,the hole path is always turned on and the AHP region maintains low potential.Thus,the peak electric field at the bottom of the trench gate is reduced and the BV value is increased by 10.7%.During the turn-on process,the low-voltage AHP region shields the gate electric field,which decreases the Miller capacitance C_res by 67%,and thus obtains a better V_cesat-E_off trade-off relationship.The JFET channel that is not fully pinched off during short-circuit causes the AHP region to act as a hole path,and the hole current through hole path accounts for 16%of the total current,thereby effectively suppressing device latch-up and improving the short-circuit capability of the device.From the perspective of controlling the electron path during short-circuit,an IGBT device with Embedded Ballast Resistor?EmBR?is proposed.The short-circuit current model of the proposed structure is established and predicts the inhibition of the EmBR-IGBT key structure parameters to short-circuit current.Different from the conventional ballast resistor structure,the proposed ballast resistor is embedded in the P-type base region and does not affect the BV value of the device.Moreover,the EmBR region is influenced by the injection enhancement effect of gate voltage during normal conduction,therefore the on-state and the threshold voltage are equal to those of the conventional structure.When the device is turned on during short-circuit,the resistance of the EmBR region increases,which lowers the effective voltage V_ge,and reduces the short circuit current by 33.7%.By tunning the key parameters of the EmBR region,the short-circuit withstand time can be adjusted within 12.2-20.3?s.On the basis of maintaining the same on-state voltage as the conventional structure,the short-circuit withstand time of the proposed IGBT can be increased by 60.6%.