Effect of Interfacial Oxide Thickness on 1/f Noise in Polysilicon Emitter BJTs

1/f noise in SiGe HBTs fabricated on CMOS-compatible thin-film SOI

“…While 1/f noise in the bulk device follows a clear I B 2 dependence, the SiGe HBT-on-SOI shows a I B 2 trend only at high I B , with a linear dependence on I B at low base currents, suggesting that in this current range noise may originate from carrier mobility fluctuations. The I B dependent 1/f noise spectrum is consistent with the presence of a large leakage current due to space-charge region G/R recombination centers, as observed in [15,16] and in previous studies on the proton radiation response in bulk SiGe HBTs [11,13].…”

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

“…The areal dependence with increasing normalized noise in npn BJTs with smaller emitter area A E is shown in Figure 2, using the SPICE parameter K F defined from The data for more than 150 devices are collected from [10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27], and shown in Figure 2 with some points omitted for clarity. Since the numbers spread over several decades, we use geometric averaging technique [28] to extract the trend in the data from the product A E ×K F ; and the trend is A E ×K F ≈5.6×10 -9 µm 2 with logarithmic standard deviation of σ dB =3.4dB.…”

“…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.…”

“…Typical types of cross-over in the noise in BJT are between areal and peripheral noise sources in the emitter region [14,21,35,36,42,60], noise from tunneling through IFO and series resistances (carrier number fluctuation, or coupled noise to the injection process, precisely) and diffusion noise (mobility fluctuation, or intrinsic noise of the current flow in emitter and base regions) [10,19,21,32,42,61,62], surface and bulk noise sources [14,21,24,36,37,42,60], and for very small-area BJTs (A E ≤0.1µm 2 ), the extension length of the base to the contact via becomes an issue for the low-frequency noise [36,37], since that extension is with large area compared to A E , and it is vulnerable to the surface noise from the oxide on the top of the structure. Also, in small-area BJTs, the crossover between generation-recombination (GR), random telegraph signal (RTS) and 1/f noise becomes apparent [11,12,17,18,30,35,63].…”

“…(11). This linear dependence is usually used to identify the diffusion noise in BJT [19,32,42] after splitting the total noise into linear and quadratic functions of the DC current, because other noise sources result in non-linear dependence between noise and DC currents. For example, S I ∝I DC 2 for recombination noise at the base surface or at the surface of the emitter-base space-charge region [42].…”