Electric-Field-Dependence Mechanism for Cosmic Ray Failure in Power Semiconductor Devices

This article describes an analysis of the electric-field-dependence mechanism for cosmic ray failure in power semiconductor devices. Two major modes for the failure have been reported. One is bipolar transistor activation caused by carrier generation from impact ionization at the n
^-
/n
⁺
boundary. The other is Joule heating generated by an avalanche current in high electric fields. We clarified that a bipolar transistor activation mode had not occurred even under high electric field conditions for the drift layer width used in lower-voltage-class insulated-gate bipolar transistors (IGBTs) by evaluating the drift layer thickness dependence of the failure in time (FIT) in 1700 V devices from punchthrough to non-punchthrough with and without a p
⁺
collector layer. We also clarified that the electric field averaged over the depletion layer width (applied voltage divided by the depletion layer width) is the critical factor for failure, rather than the maximum electric field, for the first time by observing a universal curve of the average electric field dependence of FIT in 750-6500 V IGBTs and diodes. To improve the cosmic ray durability of power semiconductor devices, lowering the electric field averaged over the depletion layer width is effective for device design.