高压IGBT雪崩鲁棒性的研究

Study on avalanche ruggedness of high voltage IGBTs

随着绝缘栅双极晶体管(insulated gate bipolar transistor,IGBT)电压等级的提升和电流容量的增大,雪崩效应已成为限制器件安全工作区(safe operating area,SOA)的重要因素.雪崩发生后IGBT背面p+n结的空穴注入是其雪崩效应区别于其他器件的主要特征.本文通过理论分析与数值模拟的方法研究了IGBT雪崩击穿特性以及雪崩产生电流丝的性质,揭示了控制雪崩产生电流丝性质的物理机制.结果表明IGBT背面的空穴注入导致其雪崩击穿曲线上产生额外的负微分电阻分支;器件共基极电流增益α_(pnp)是决定雪崩产生电流丝的关键因素,随着α_(pnp)的增大,雪崩产生的电流丝强度越强、移动速度越慢,从而导致器件的雪崩鲁棒性越弱.

With the increase of IGBT voltage and current ratings,the avalanche effect has become an important factor limiting the safe operating area(SOA)of the device.The hole injection of the p+n junction on the back of the device when the avalanche effect occurs is the main feature that distinguishes the avalanche effect of the IGBT from other devices.In this paper,the avalanche breakdown characteristics of IGBT and the behavior of avalanche-generated current filaments are studied through theoretical analysis and numerical simulation,and the physical mechanism dominating the behavior of avalanche-generated current filaments is revealed.The results show that the hole injection on the backside of IGBT leads to an additional negative differential resistance branch on the avalanche breakdown curve,and the strength of the negative differential resistance effect depends on the common base current gain of IGBT α_(pnp).With the increase of α_(pnp),the negative differential resistance effect becomes stronger,the avalanche current at the valley point where the additional negative differential resistance branch transforms into the positive differential resistance branch also becomes higher.And the valley point at the avalanche breakdown curve of IGBT dominates the strength of the avalanche-generated filament.As a result,the strength of avalanche-generated filament depends on the α_(pnp).With the lattice temperature increasing,the avalanche breakdown voltage of IGBT increases,leading to the shifting of the avalanche breakdown curve towards a higher voltage.And with the increase of α_(pnp),the offset of the avalanche breakdown curves at high and low temperature becomes smaller,which dominates the lateral movement speed of the avalanche-generated filament.With the increase of the α_(pnp) and the decrease of the offset of avalanche breakdown curves at high and low temperature,the avalanche-generated filament laterally moves more slowly.To sum up,with the increase of the α_(pnp) of IGBT,the avalanche-generated filament becomes stronger and moves more slowly,which extremely causes the local overheating where the filaments exist and lowers the avalanche robustness of the device.Therefore,the α_(pnp) of IGBT must be controlled precisely in order to have a good trade-off between the characteristics and the reliability of IGBT.