Investigating the differences in low-frequency noise behavior of npn and pnp SiGe HBTs fabricated in a complementary SiGe HBT BiCMOS on SOI technology

Low-frequency noise in downscaled silicon transistors: Trends, theory and practice

“…We also observe that the data are very close to the trend in Figure 4, when re-calculating the average thickness of IFO from the information in [20]. However, despite that exponential functions of t IFO are used in the above model for several quantities, the overall dependence of noise level vs. average t IFO remains a power law and we note that the exponential dependence of noise on t IFO , although observed in [14,33,34] experimentally, is not explained theoretically yet. Nevertheless, the approach in [20] provides a way to analyze noise from non-uniform IFO in BJT, and can help to identify different contributions to the total low-frequency noise in deep sub-micron BJT, in which a crossover between several noise sources is obvious; and this will be discussed next.…”

“…exp(t IFO /λ), proposed in [14] empirically, can also fit some data. This is illustrated with another dash-line which fits the triangles in Figure 4 for the noise in SiGe HBTs [33,34]. The values for λ, however, scatter; λ≈0.5nm for the data from [14] (open diamonds in Figure 4), while λ≈0.4-0.5nm…”

“…for the data from [33,34] (solid triangles in Figure 4), reaching a value, which is difficult to explain physically, even for the direct tunneling of holes. The effective mass of holes is high in SiO 2 and therefore have shorter tunneling attenuation distance λ<0.1nm.…”

“…The second factor for deviation of noise level around the trend in Figure 2 can be attributed to differences in the fabrication of BJT. The impact of several technology steps on the low-frequency noise in polysilicon emitter BJTs was reviewed several times, for example in [31], and extensively analyzed in the past [18,19,20,21,32,33,34,35,36,37,38,39,40]. From these studies, it is found that among the many sources that can contribute to the low-frequency noise, such as fluctuation in diffusion, surface recombination and charge trapping, the major noise source is associated with or located in the interfacial oxide (IFO) between poly and monosilicon layers in the emitter of BJT.…”

“…Observe that a small increase of t IFO with about 0.5nm results in a large increase in the level of the low-frequency noise, approximately 2 decades for the values of the noise coefficient K F . A better view of the data in npn BJTs is given in Figure 4, together with data for other types of BJT from [32,33,34], and the data are analyzed in a manner similar to previous discussion in [29]. The data are available in numerical form in [41].…”