Reliability of SiGe HBTs in Long-Term Operation

The main reliability issue in SiGe HBTs is the cumulative degradation of the base current occurring during combined high collector voltage, high emitter current stress. This ageing is the result of the interplay between oxide interface trap creation and annihilation. Long-term stress tests show that the ageing rate varies significantly over time, reveals saturation behavior, and depends in a much more complex way on stress load as previously assumed. At high enough junction temperatures degradation can be reversed leading to efficient thermal recovery of the HBTs. With simple duty cycles switching between ageing and recovering states it could be demonstrated that pure DC stress represents an upper limit for degradation in SiGe HBTs.