Low-frequency noise properties of SiGe heterojunction bipolar transistors

In this study, we investigated the low-frequency noise in SiGe heterojunction bipolar transistors (HBTs) with and without a selectively implanted collector (SIC). By comparing the magnitude of I If noise, collector current, and current gains of the SiGe HBTs with and without SIC we show that the impurities at the collector produced by the incomplete activation of the implanted ions cause an increase in the collector current I If noise spectrum. Thus, SiGe HBT with SIC exhibits higher collector noise current spectra due to the inactive ions in the collector. The figures-of-merit of noise corner frequency (fc) to cutoff frequency ratio (f(r)), f(c)/f(T)., indicates that the SiGe HBT without SIC has a better low-frequency noise property for circuit application prior to the f(T) roll-off. Furthermore, at the onset of high injection effect, the conspicuous degradation of high-frequency properties also deteriorates the f(c)/f(t) ratio of SiGe HBT without SIC.