Impact of reverse EB stress and mixed-mode stress on low-frequency noise for SiGe HBTs in forward and inverse modes

We present in this work the impact of electrical reliability stress on low-frequency noise for SiGe HBTs in forward and inverse modes. The reverse EB stress and the forward mixed-mode stress are investigated. For the first time inverse mode noise is used as a tool to investigate stress-induced damage. The fact that reverse EB stress degrades SiGe HBTs low-frequency noise in the forward mode but not in the inverse mode indicates that the stress-induced traps are located in the EB spacer oxide. Mixed-mode stress degrades both the forward and inverse modes low-frequency noise, consistent with the theory that both the EB and CB junctions are damaged during the stress. The observed noise degradation under stress calls for accurate noise aging modeling in reliability simulation.