Avalanche-induced 1/f noise in bipolar transistors

It has been proposed that degradation of low current hFE, as a result of avalanching the emitter-base junction of a bipolar transistor, can be attributed to an increase in surface recombination velocity within the emitter-base space-charge region. This work shows that 1/fnoise is also increased during avalanche and that this increase is consistent with a previously reported correlation between surface recombination velocity and 1/fnoise.     

Bipolar transistors with low 1/f noise

Bipolar transistors employing low concentration emitter diffusion were obtained which show no current gain fall-off at low current levels, as well as significantly reduced 1/f noise. These devices may favourably be applied in low noise amplifiers.     

1/f noise in n-channel silicon-gate MOS transistors

It is found that equivalent gate noise power for l/f noise in n-channel silicon-gate MOS transistors at near zero drain voltage at room temperature is empirically described by two noise terms, which vary asK_{1}(q/C_{ox}) (V_{G} -V_{T})/f and K_{2}(q/C_{ox})^{2}/f, where V_{G}is gate voltage, VTis threshold Voltage, and Coxis gate-oxide capacitance per unit area. Unification of carrier-density fluctuation (McWhorter's model)and mobility fluctuation (Hooge's model) can account for the experimental data. The comparison between the theory and experiment shows that the carrier fluctuation term K2is proportional to oxide-trap density at Fermi-level. The mobility fluctuation term K1is correlated to K2, being proportional toradic K_{2}. The origin of this correlation is yet to be clarified.     

Hole-induced 1/f noise increase in MOS transistors

This paper presents experimental evidence for hole-generated 1/f noise traps in gate oxides near the MOS interface. To clarify the microscopic nature of noise traps, 1/f noise is measured in Si MOS transistors in which carriers are intentionally injected into the gate oxides. It was found that 1/f noise increases more rapidly after drain avalanche hot-carrier injection than after channel hot-electron injection. A rapid noise increase is also observed after X-ray irradiation. These results show that the increase in 1/f noise is closely related to holes. We propose a model in which the reaction between holes and oxygen vacancies near the interface creates noise traps, i.e., E' centers and fixed positive charges     

1/f noise in modulation-doped field effect transistors

Low frequency noise measurements are reported in modulation-doped GaAs field effect transistors. The noise spectrum is1/fand is relatively large. At a given frequency the equivalent saturated diode current Ieqvaries as V2, as expected for a fluctuating resistor, and saturates when the characteristic saturates.     

Origin of 1/f noise in bipolar transistors

In planar n-p-n transistors fabricated in IC technology, the dependence of 1/fnoise on the base current density jB, the base width WB, and the emitter area FEwas measured. The power spectrumS_{iB}(f)of the base current fluctuations iBcan be represented by the empirical relationS_{iB} = const. jmin{B}max{gamma} cdot Fmin{E}max{beta} cdot wmin{B}max{-1} cdot f^{-1}where1 leq gamma leq 2and β has been found to be 1.3 or 2. The results of measurements on gate-controlled devices indicate that 1/fnoise cannot be explained by McWhorter's surface model. Therefore, a new model is proposed which assumes resistance fluctuations in the base region as the cause of 1/fnoise in bipolar transistors. The model establishes the relation forS_{iB}(f)as well as the magnitude of the coefficients β and γ.     

Surface states and 1/f noise in MOS transistors

Surface-state density in n-channel MOS transistors operating in the inversion mode has been determined from the channel conductance and related to 1/fnoise in these devices. It has been found that the noise is proportional to the surface-state density at the Fermi level. The surface orientation and temperature affect the noise output only indirectly, through their influence on the surface-state density and the position of the Fermi level at the surface.     

1/f voltage noise in silicon planar bipolar transistors

Measurements on silicon planar transistors in the frequency range 1 Hz?1 kHz have shown conclusively that 1/f noise is present on the equivalent input noise-voltage generator. In some samples of transistors, correlation between the 1/f components of voltage and current noise was detected. In one sample, an estimate of the correlation coefficient was made, the result being a coefficient of approximately ?0.1.     

Characterization of low 1/f noise in MOS transistors

By careful processing MOS transistors have been fabricated with a low value of the interface states density (2 × 10¹⁰/cm²eV). Consequently the1/fnoise in these devices is low and in the same order of magnitude as for junction FETs. The experimental values of the equivalent noise voltage and the equivalent noise current are compared to an expression derived from straight physical arguments. From the comparison it is concluded that the noise equivalent voltage in saturated operation is proportional to the effective gate voltage, the interface state density, and inversely proportional to the gate input capacitance. Moreover, it is concluded that a proper heat treatment not only reduces the number of states but also removes the near bandedge peaks, which usually appear in the trap distribution function.     

Temperature dependence of 1/f noise in polysilicon-emitter bipolar transistors

1/f noise was measured on polysilicon-emitter bipolar n-p-n and p-n-p transistors over a temperature range of 173K相似文献   

Theory of 1/f noise in bipolar silicon planar transistors

A theory of 1/f low-frequency noise in silicon planar transistors is developed. It relates this noise to fluctuations in base current produced by fluctuations of occupied traps in the silicon dioxide. It is shown that the theoretical relationship of noise is consistent with experiment.     

Fully-depleted SOI CMOS for analog applications

Fully-depleted (FD) SOI MOSFETs offer near-ideal properties for analog applications. In particular their high transconductance to drain current ratio allows one to obtain a higher gain than from bulk devices, and the reduced body effect permits one to fabricate more efficient pass gates. The excellent behavior of SOI MOSFETs at high temperature or at gigahertz frequencies is outlined as well     

Tradeoff between 1/f noise and microwave performance in AlGaAs/GaAsheterojunction bipolar transistors

The 1/f noise characteristics and microwave gain of AlGaAs/GaAs heterojunction bipolar transistors (HBT's) have been investigated as a function of surface passivation ledge length. These measurements clearly demonstrate that the ledge length imposes a tradeoff between the 1/f noise and microwave power gain performance. Compared to a conventional unpassivated self-aligned HBT, HBT's with 0.4 and 1.1 μm ledge lengths improve the equivalent input base noise current spectral density at 100 Hz by as much as 2 dB and 6.5 dB, respectively; while degrading the maximum available gain at 18 GHz by 0.3 dB and 2.4 dB, respectively     

Leakage currents, surface current and 1/f noise in planar bipolar transistors

Using arguments based on the d.c. equivalent circuit of a planar bipolar transistor, it is shown that the ratio ICEO/ICBO is a measure of the significance of surface recombination current. Measurements of 1/f noise and ICEO/ICBO for a variety of transistors provide new evidence that the 1/f noise is due to the surface recombination current.     

1/f noise

1/f noise is a nonstationary random process suitable for modeling evolutionary or developmental systems. It combines the strong influence of past events on the future and, hence somewhat predictable behavior, with the influence of random events. Nonstationary autocorrelation functions for 1/f noise are developed to demonstrate that its present behavior is equally correlated with both the recent and distant past. The minimum amount of memory for a system that exhibits 1/f noise is shown to be one state variable per decade of frequency. The system condenses its past history into the present values of its state variables, one of which represents an average over the most recent 1 unit of time, one for the last 10 time units, 100 units, 1000, 10000, and so on. Each such state variable has an equal influence on present behavior.     

Measurement and comparison of 1/f noise and g-r noise in siliconhomojunction and III-V heterojunction bipolar transistors

This paper experimentally determines and compares the 1/f noise and the g-r noise, as components of the base noise current spectral density, in Si homojunction and III-V heterojunction bipolar transistors (HBTs) in common-emitter configuration. The noise spectra for each of these devices are obtained as functions of the base bias current (I_B), and the 1/f noise has been found to depend on I_B as I_B^γ, where γ~1.8 for the silicon BJT's and InP/InGaAs HBT's with high current gains (β~50), and γ~1.1 for the AlGaAs/GaAs HBTs with low current gains (4<β<12). The nearly constant current gain and the near square-law and inverse-square emitter area dependence of 1/f noise in silicon devices are indicative of the dominant base bulk recombination nature of this noise. The 1/f noise in the InP based HBTs has been found to be lowest among all the devices we have tested, and its origin is suggested to be the base bulk recombination as in the Si devices. For the AlGaAs/GaAs HBTs, the low current gain and the near unity value of γ, arise most likely due to the combined effects of surface, bulk, and depletion region recombinations and the base-to-emitter injection. The dependence of the 1/f noise on the base current density in the devices tested in this work, and those tested by others are compared to find out which HBT's have achieved the lowest level of 1/f noise     

On the geometry dependence of the 1/f noise in CMOS compatiblejunction diodes

This paper examines in detail the low-frequency (LF) noise behavior of Si n⁺p junction diodes in forward operation. Diodes fabricated on various types of Si substrates (FZ, epitaxial, and Cz) and with different geometries are studied in the current range 0.1-250 μA in order to investigate the impact of these parameters. It is demonstrated that different kinds of 1/f noise behavior can be distinguished which point toward a different origin. The nature of the 1/f noise is most clearly identified by inspecting the variation of the frequency exponent with forward bias. On the one hand, what could be called “peripheral” or “surface” 1/f noise shows a frequency exponent which reduces with increasing forward current, a trend which is also observed for the corresponding ideality factor. When the 1/f noise is predominantly generated in the volume of the material (bulk origin), a more or less constant frequency exponent is found. It is also concluded that in many cases, no unique area or perimeter dependence is found when comparing the noise power spectral density of diodes with a different geometry. It will finally be shown that there exists a close correlation between the different 1/f noise sources and the different reverse current components, which are a sensitive function of the starting material characteristics and processing details     

Body bias dependence of 1/f noise in NMOS transistors fromdeep-subthreshold to strong inversion

Dependence of 1/f noise on the body-to-source junction bias voltages (V_BS) between -2.5 and 0.5 V for 0.25-μm NMOS transistors is reported. In subthreshold, 1/f noise is reduced by about one order of magnitude, when the body-to-source junction is forward biased by 0.5 V (V_BS) compared to that for V_BS=0 V, which is due to increased depletion layer capacitance as well as possibly due to an increased average distance between oxide traps and carriers caused by the forward bias. On the contrary, in strong inversion, 1/f noise remains almost constant for the entire V_BS range     

A CMOS analog front-end IC for portable EEG/ECG monitoring applications

A new digital programmable CMOS analog front-end (AFE) IC for measuring electroencephalograph or electrocardiogram signals in a portable instrumentation design approach is presented. This includes a new high-performance rail-to-rail instrumentation amplifier (IA) dedicated to the low-power AFE IC. The measurement results have shown that the proposed biomedical AFE IC, with a die size of 4.81 mm/sup 2/, achieves a maximum stable ac gain of 10 000 V/V, input-referred noise of 0.86 /spl mu/ V/sub rms/ (0.3 Hz-150 Hz), common-mode rejection ratio of at least 115 dB (0-1 kHz), input-referred dc offset of less than 60 /spl mu/V, input common mode range from -1.5 V to 1.3 V, and current drain of 485 /spl mu/A (excluding the power dissipation of external clock oscillator) at a /spl plusmn/1.5-V supply using a standard 0.5-/spl mu/m CMOS process technology.     

The total dose effects on the 1/f noise of deep submicron CMOS transistors

Using 0.18 μm CMOS transistors, the total dose effects on the 1/f noise of deep-submicron CMOS transistors are studied for the first time in mainland China. From the experimental results and the theoretic analysis, we realize that total dose radiation causes a lot of trapped positive charges in STI （shallow trench isolation） SiO2 layers, which induces a current leakage passage, increasing the 1/f noise power of CMOS transistors. In addition, we design some radiation-hardness structures on the CMOS transistors and the experimental results show that, until the total dose achieves 750 krad, the 1/f noise power of the radiation-hardness CMOS transistors remains unchanged, which proves our conclusion.