Turn-off switching analysis considering dynamic avalanche effect for low turn-off loss high-voltage IGBTs

An avalanche generation phenomenon has a large influence on turn-off switching loss and reverse-biased safe operating area of high-voltage insulated gate bipolar transistors (IGBTs). The purpose of this paper is to clarify the correlation between the avalanche multiplication phenomenon and the turn-off characteristics. We introduce a turn-off switching analytical model of IGBTs that considers the avalanche multiplication effect. It is concluded that the criterion of dynamic avalanche depends on the gate resistance. In the case of 4.5-kV IGBTs, the gate resistance of more than 200 Ω·cm² is needed to suppress the dynamic avalanche generation under a clumped inductive load circuit. On the contrary, the turn-off switching loss increases in the case that the gate resistance R_G is increased to more than approximately 100 Ω·cm². Theses results show that to realize low turn-off switching loss, it is necessary to ensure that the gate resistance is below a constant value, such as 100 Ω·cm². However, at high current density, such as 80 A/cm², the dynamic avalanche will generate under such small gate resistance condition. Therefore, it is important to develop IGBTs without destruction even under the condition of dynamic avalanche generation.