Theory of low frequency noise in Si MOST's
TL;DR: In this paper, the authors deal with the theory of low frequency noise in MOST's due to traps with a wide spread of relaxation times, and show that the effect of traps on noise amplitude depends on their surface state efficiency, a parameter which is directly accessible to measurement.
Abstract: The paper deals with the theory of low frequency noise in MOST's due to traps with a wide spread of relaxation times. Particular attention is paid to the case when the drain voltage is small. Distributions of relaxation times leading to a 1/ƒα noise spectrum are discussed (1 ⩽ α < 2). It is shown that for any given noise spectrum, the effect of traps on noise amplitude depends on their ‘surface state efficiency’, a parameter which is directly accessible to measurement. The validity of this trapping model of noise can therefore be tested using equations which relate noise with other measurable parameters of the device.
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TL;DR: In this paper, a unified flicker noise model which incorporates both the number fluctuation and the correlated surface mobility fluctuation mechanism is discussed, which can unify the noise data reported in the literature, without making any ad hoc assumption on the noise generation mechanism.
Abstract: A unified flicker noise model which incorporates both the number fluctuation and the correlated surface mobility fluctuation mechanism is discussed. The latter is attributed to the Coulombic scattering effect of the fluctuating oxide charge. The model has a functional form resembling that of the number fluctuation theory, but at certain bias conditions it may reduce to a form compatible with Hooge's empirical expression. The model can unify the noise data reported in the literature, without making any ad hoc assumption on the noise generation mechanism. Specifically, the model can predict the right magnitude and bias dependence of the empirical Hooge parameter. Simulated flicker noise characteristics obtained with a circuit-simulation-oriented flicker noise model based on the new formulation were compared with experimental noise data. Excellent agreement between the calculations and measurement was observed in both the linear and saturation regions for MOS transistors fabricated by different technologies. The work shows that the flicker noise in MOS transistors can be completely explained by the trap charge fluctuation mechanism, which produces mobile carrier number fluctuation and correlated surface mobility fluctuation. >
841 citations
TL;DR: In this paper, the authors measured the apparent interface density in the whole band gap of silicon and showed that the apparent inteiface density can contain a contribution of defects unspecific of the interface, for instance, spatial fluctuation of the interfaces or silicon defects introducing a deep level in the band gap.
492 citations
TL;DR: An overview of recent issues concerning the low frequency (LF) noise in modern CMOS devices is given and the approaches such as the carrier number and the Hooge mobility fluctuations used for the analysis of the noise sources are presented and illustrated through experimental results obtained on advanced CMOS generations.
343 citations
TL;DR: In this paper, a modified trapping noise theory based on the McWhorter's assumptions and valid in all the working regimes is developed to account for this behavior, and excellent agreement is obtained with the variations of several parameters: gate and drain biases, geometry, oxide and depletion capacitance, temperature, and technologies.
Abstract: Low-frequency 1/f noise in Si n-channel MOSFET's is measured from weak to strong inversion, through the relative spectral density of the drain current fluctuations S_{I}_{D}/I^{2}_{D} . Under specific conditions, a plateau is observed in the variations of S_{I}_{D}/I^{2}_{D} versus the gate voltage in weak inversion followed by a steep decrease in strong inversion. A modified trapping noise theory based on the McWhorter's assumptions and valid in all the working regimes is developed to account for this behavior. Excellent agreement is obtained with the variations of several parameters: gate and drain biases, geometry, oxide and depletion capacitance, temperature, and technologies. The influence of fast interface states is particularly studied and is related to the noise variations and the oxide trap densities.
318 citations
TL;DR: In this article, a physics-based MOSFET noise model that can accurately predict the noise characteristics over the linear, saturation, and subthreshold operating regions is presented.
Abstract: Discussed is a physics-based MOSFET noise model that can accurately predict the noise characteristics over the linear, saturation, and subthreshold operating regions but which is simple enough to be implemented in any general-purpose circuit simulator. Expressions for the flicker noise power are derived on the basis of a theory that incorporates both the oxide-trap-induced carrier number and correlated surface mobility fluctuation mechanisms. The model is applicable to long-channel, as well as submicron n- and p-channel MOSFETs fabricated by different technologies, and all the model parameters can be easily extracted from routine I-V and noise measurements. >
245 citations
References
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TL;DR: In this article, the low frequency noise voltage spectrum for a MOS transistor is calculated under the assumption that a time constant dispersion, giving a 1/ε − spectrum, is caused by tunneling of carriers at the silicon-silicon oxide interface to traps located inside the oxide.
Abstract: The low frequency noise voltage spectrum for a MOS transistor is calculated under the assumption that a time constant dispersion, giving a 1/ƒ- spectrum , is caused by tunneling of carriers at the silicon-silicon oxide interface to traps located inside the oxide. The magnitude of the noise from different trap distributions is calculated. The largest noise contribution is shown to come from traps near the quasi Fermi level of the current carriers in the channel. The influence of temperature and operating point on the noise is examined. The theoretically predicted noise magnitude agrees with the experimental results (presented in Part II). The theory presented describes qualitatively the shape of the low frequency noise spectrum.
422 citations
TL;DR: In this article, the authors proposed a tunnelling-via-local-state model for the excess current in silicon junctions, which was shown to be applicable to excess currents in other materials.
Abstract: At low forward biases, a high current flows in Esaki junctions due to band-to-band tunnelling. At sufficiently high biases the current flows by normal forward injection. Between these two bias ranges, the current is unexpectedly high and has been called the excess current. A comprehensive experimental study has been made of this excess current in silicon junctions. It is shown that the properties of the excess current observed so far can be accounted for by a mechanism originally suggested by Yajima and Esaki, in which carriers tunnel by way of energy states within the forbidden gap. Based on this model, the following expression for the excess current, ${I}_{x}$, is proposed: ${I}_{x}\ensuremath{\sim}{D}_{x}\mathrm{exp}{\ensuremath{-}(\frac{{\ensuremath{\alpha}}_{x}{W}_{1}{e}^{\frac{1}{2}}}{2})[\ensuremath{\epsilon}\ensuremath{-}e{V}_{x}+0.6e({V}_{n}+{V}_{p})]},$ where ${D}_{x}$ is the density of states in the forbidden gap at an energy related to the forward bias, ${V}_{x}$, and the Fermi energies on the $n$ and $p$ sides are ${V}_{n}$ and ${V}_{p}$, respectively, $e$ is the electron charge, $\ensuremath{\epsilon}$ is the energy gap, ${W}_{1}$ is the junction width constant, and ${\ensuremath{\alpha}}_{x}$ is a constant containing a reduced effective mass, ${m}_{x}$. This formula describes the observed dependence of ${I}_{x}$ (i) on ${D}_{x}$, observed by introducing states associated with electron bombardment, (ii) on $\ensuremath{\epsilon}$, studied by the temperature variation of the diode characteristics, (iii) on ${V}_{x}$, verified from semilogarithmic plots of the forward characteristics, and (iv) on ${W}_{1}$, tested by using junctions of different widths. From these experiments, ${m}_{x}=0.3{m}_{0}$ to within a factor of 2.The origins of the states in the band gap are not known for certain though they are most likely the band edge tails inherent to heavily doped semiconductors. It is probable that the tunnelling-via-local-states model for the excess current in silicon is applicable to excess currents in other materials.
284 citations
IBM1
TL;DR: In this article, the authors measured the effective mobility, field effect mobility, Hall mobility, and carrier density of Si as a function of field perpendicular to the surface, and reported that at all temperatures from 42 to 300, at least one maximum in the mobility was observed.
Abstract: Measurements of the effective mobility, field effect mobility, Hall mobility, and carrier density of Si as a function of field perpendicular to the surface are reported At all temperatures from 42 to 300\ifmmode^\circ\else\textdegree\fi{}K, at least one maximum in the mobility was observed The temperature dependence is reported for different fields At room temperature, a single maximum in the mobility was observed close to the threshold for inversion As the temperature was lowered, this peak increased At temperatures near 80\ifmmode^\circ\else\textdegree\fi{}K, it then decreased Another maximum appeared at about 100\ifmmode^\circ\else\textdegree\fi{}K at higher fields; it increased as the temperature was lowered An anomalous shift in the conductance threshold between 773 and 42\ifmmode^\circ\else\textdegree\fi{}K is reported and is correlated with the charge in the oxide Effects of substrate bias are reported Some comments are made on possible scattering mechanisms The effect of interface states was measured and their density near the conduction band is reported
272 citations
139 citations
TL;DR: In this paper, the authors show that at low frequencies this modulation is the dominant effect, giving rise to a noise power spectrum which resembles 1/f noise at high frequencies, where only thermal noise in the channel and input noise are of importance, and MOS triodes are similar to junction field effect devices from the noise point of view.
Abstract: Noise in MOS diodes arises from different sources: fluctuations in occupation of surface states, shot noise, and leakage noise. Fluctuations in the occupation of surface states produce changes in the surface space-charge distribution which in turn produce currents. Shot noise is produced by fluctuations of the individual drift and diffusion flows toward the surface. Leakage noise is associated with the small flow of current through the oxide. In MOS triodes these three mechanisms give rise to gate noise and thus input noise in the amplifier, but the first one produces an important indirect effect. Fluctuations in the occupation of interface states result in modulation of the channel conductance. At low frequencies this modulation is the dominant effect, giving rise to a noise power spectrum which resembles 1/f noise. At high frequencies, where only thermal noise in the channel and input noise are of importance, MOS triodes are similar to junction field effect devices from the noise point of view.
109 citations