Impact of Technological Parameters on the Low Frequency Noise of Advanced Heterojunction Bipolar Transistors

Usually, the 1/f noise sources in heterojunction bipolar transistors (HBTs) are located in the intrinsic emitter-base (E-B) volume, either in the E-B junction space charge region or at the polycrystalline-silicon/monocrystalline-silicon interface in the neutral emitter layer. In this paper, to probe more accurately the location of the noise sources responsible for the 1/f noise, investigations on different HBTs fabricated with different technological parameters are undertaken. First, we have shown that carbon content has a negligible influence on 1/f noise level, but for high carbon content significant generation-recombination (G-R) noise components appear. Second, by studying influence of the emitter-base junction depth, we have shown that the 1/f noise sources are located at the polycrystalline-silicon/monocrystalline-silicon interface. Using statistical estimators, we have studied and modelled the dispersion of the 1/f noise. It was found that the dispersion in the noise level increases as the inverse of the square root of the emitter area, similar to what was previously found for silicon homojunction transistors.