1/f noise in inhomogeneous condensed media: Relation with a nonequilibrium phase transition

An approach in which the spectral density of a noise signal, varying inversely as the frequency with a fractal exponent close to 1, is due to the inhomogeneity of the medium is proposed. In the critical region the nucleation process serves as the source of inhomogeneity. Yu. Fed’kovich Chernovtsy State University Pis’ma Zh. Tekh. Fiz. 25, 1–5 (September 26, 1999)     

Self-organization of a critical state and 1/f fluctuations caused by the interaction of phase transitions in a distributed system

A mathematical model is proposed that describes the appearance of fluctuations with a spectral density inversely proportional to the frequency as a result of the intersection of phase transitions in a spatially inhomogeneous system. The model is represented by a set of two nonlinear stochastic differential equations with mutually interacting order parameters. It is demonstrated that a random walk in the model potential field corresponding to the intersecting sub-and supercritical phase transitions may lead to the self-organization of a critical state and the appearance of fluctuations with a 1/f spectral density.     

2.27 1/f noise voltage in a thin film structure

1/f noise in current carrying thin film devices is caused by fluctuation of the electrical conductivity of the film material. Describing its effect on the voltage distribution in a device requires a two-dimensional analysis. This may be done by means of a theory, presented in this article, where the fluctuation is treated as current dipoles.The geometrical dependence of the noise intensity across electrodes on Hall generator structures, made from InSb thin films, is measured. This is in fair agreement with predictions based on the theory.     

1/f noise of electrolytic capacitors as a reliability indicator

The electrical noise of capacitors and the relationship between typical imperfections in capacitors and their excess noise are described. It was assumed that a noisy capacitor is a poor-quality one. Investigations were aimed at the determination of a correlation between the inherent noise of capacitors and their reliability (time to failure) and also at the determination of an indicator to predict reliability. Investigations (noise measurements and reliability tests) were carried out on two samples of aluminium electrolytic capacitors. The method of reliability prediction for electrolytic capacitors based on their low-frequency noise is described. For reliability prediction the noise intensity G at a frequency of 2 Hz was used as a reliability indicator. It was found that the evaluated correlation coefficients between the noise parameter G and the time to failure, t, are statistically significant. It is concluded that it is possible to predict the lifetime of aluminium electrolytic capacitors on the basis of their 1/f noise. © 1998 John Wiley & Sons, Ltd.     

Quality and 1/f noise of electronic components

Classification rules of electronic components based on their 1/f noise measurements are presented. It is proposed to classify electronic components into four groups with different quality: high, good, low, poor. The results of investigations of type BF 414 transistors are reported.     

Computational model of nonequilibrium phase transitions in a Si-Ge system

A computational model of a Si-Ge system melting and solidification induced by pulsed-laser irradiation is presented in the paper. Phase transitions in the system are modeled using the theory of transition states so that undercooling or overheating of the interface and kinetic phase diagrams are taken into account. The computational solution of the mathematical model is performed using the Galerkin finite element method in a one-dimensional approximation and the moving boundary problem is solved by a front-fixing technique. In a practical application of the model, the melting and solidification of both Si-Ge alloys of various composition and thin Ge layers on the Si bulk induced by ArF excimer laser are simulated. The results of numerical simulations are compared with the available experimental data.     

再论1/f噪声的动力学统计理论

在《1/f噪声的动力学统计理论》一文中,为了突出重点,攻克主要矛盾,因而对1/f噪声的某些特点,如实验上发现的1/f噪声的功率谱S(f)为什么总是1/fM能谱和功率谱S(f)为何是同一函数等等,当时未能深入追究,本文除了弥补这些不足之外,还从“零点能”与“暗物质”而引发的“背景能量的涌动”这个深层次上来解释普适关系式:S(f)∝logf/f。     

Nonequilibrium phase transitions induced by external noise in distributed systems

A formalism is proposed to describe nonequilibrium phase transitions induced by external multiplicative noise in distributed systems. This approach can reduce the problem to an investigation of a regular differential equation whose roots correspond to possible phase states in the system. By means of this theory the relative probability of the existence of one state can be compared with another and the number of possible states identified, and the genesis of the system under the action of fluctuations of the external medium can be traced. Pis’ma Zh. Tekh. Fiz. 25, 91–95 (February 26, 1999)     

On the 1/f frequency noise in ultra-stable quartz oscillators

The frequency flicker of an oscillator, which appears as a 1/f3 line in the phase noise spectral density, and as a floor on the Allan deviation plot, originates from two basic phenomena, namely, (1) the 1/f phase noise turned into 1/f frequency noise via the Leeson effect, and (2) the 1/f fluctuation of the resonator natural frequency. The discussion on which is the dominant effect, thus on how to improve the stability of the oscillator, has been going on for years without giving a clear answer. This article tackles the question by analyzing the phase noise spectrum of several commercial oscillators and laboratory prototypes, and demonstrates that the fluctuation of the resonator natural frequency is the dominant effect. The investigation method starts from reverse engineering the oscillator phase noise in order to show that if the Leeson effect was dominant, the resonator merit factor Q would be too low as compared to the available technology.     

Measurement of 1/f noise and its application in materials science

This is a review of the measurement of 1/f noise in certain classes of materials which have a wide range of potential applications. This includes metal films, semiconductors, metallic oxides and inhomogeneous systems such as composites. The review contains a basic introduction to this field, the theories and models and follows it up with a discussion on measurement methods. There are discussions on specific examples of the application of noise spectroscopy in the field of materials science.     

Correlation between 1/f noise and semiconductor laser degradation

The origin of the increase in residual spectral linewidth during device degradation is experimentally and theoretically clarified in a multiple quantum well (MQW) distributed feedback (DFB) laser. Non-radiative recombination current increases during device degradation and causes 1/f noise to increase. This current 1/f noise is the origin of the increase in the residual spectral linewidth. Through these degradation behaviours, a model showing a correlation between 1/f noise and the semiconductor laser degradation is proposed.     

Dependence of SAW resonator 1/f noise on device size

Experiments were conducted with eight 450-MHz surface acoustic wave (SAW) resonators which demonstrate that a resonator's 1/f noise depends approximately inversely on the active acoustic area of the device. This observation is consistent with a proposed theory that 1/f noise in acoustic resonators is caused by localized velocity or dimensional fluctuations.     

Generation of 1/f noise in locked systems working in nonlinear mode

Properties of the phase fluctuations of a nonlinear oscillator were investigated. The multiscale aspect of synchronization is experimentally confirmed with the observation of lockings at any rational ratio. This global property of synchronization is associated with a local one by the study of the phase locked loop (PLL) under nonlinear conditions. We show that the discontinuity between the locking and the free-run state is characterized by the presence of slow temporal variations that induce a low frequency spectrum. An experimental verification of the increase of fluctuations confirms the classical results, which associate 1/f noise to nonlinearity, autosimilarity and regularity, represented here by the synchronization.     

Flicker (1/f) noise in tunnel junction dc SQUIDS

We have measured the spectral density of the 1/f voltage noise in current-biased resistively shunted Josephson tunnel junctions and dc SQUIDs. A theory in which fluctuations in the temperature give rise to fluctuations in the critical current and hence in the voltage predicts the magnitude of the noise quite accurately for junctions with areas of about 2 × 10⁴ µm², but significantly overestimates the noise for junctions with areas of about 6 µm². DC SQUIDs fabricated from these two types of junctions exhibit substantially more 1/f voltage noise than would be predicted from a model in which the noise arises from critical current fluctuations in the junctions. This result was confirmed by an experiment involving two different bias current and flux modulation schemes, which demonstrated that the predominant 1/f voltage noise arises not from critical current fluctuations, but from some unknown source that can be regarded as an apparent 1/f flux noise. Measurements on five different configurations of dc SQUIDs fabricated with thin-film tunnel junctions and with widely varying areas, inductances, and junction capacitances show that the spectral density of the 1/f equivalent flux noise is roughly constant, within a factor of three of (10^?10/f)? ₀ ² Hz^?1. It is emphasized that 1/f flux noise may not be the predominant source of 1/f noise in SQUIDS fabricated with other technologies.     

Up-converted 1/f PM and AM noise in linear HBT amplifiers

In this paper we describe a technique to predict the 1/f phase modulation (PM) and 1/f amplitude modulation (AM) noise due to up-conversion of 1/f baseband current noise in microwave heterojunction bipolar transistor (HBT) amplifiers. We obtain an accurate model for the amplifier and find the expression for voltage gain in terms of DC bias, transistor parameters, and circuit components. Theoretical 1/f PM and AM noise sensitivities to 1/f baseband current noise are then found by applying the definitions of PM and AM noise to the gain expression of the amplifier. Measurements of PM and AM sensitivities at 500 MHz and 1 GHz were in good agreement with the values predicted by theory, verifying the validity of this technique. This method can be used to optimize amplifier design for low PM and AM noise. We show that the amplifier PM noise can be reduced by 9 dB by adjusting the value of the input coupling capacitor.     

Structure and 1/f noise of boron doped polymorphous silicon films

The influence of structure variation on the 1/f noise of nanometric boron doped hydrogenated polymorphous silicon (pm-Si:H) films was investigated. The films were grown by the conventional radio frequency plasma enhanced chemical vapor deposition (PECVD) method. Raman spectroscopy was used to reveal the crystalline volume fraction (X(c)) and crystal size of the pm-Si:H. The measurement of optical and structure properties was carried out with spectroscopic ellipsometry (SE) in the Tauc-Lorentz model. A Fourier transform infrared (FTIR) spectrometer was used to characterize the presence of nanostructure-sized silicon clusters in pm-Si:H film deposited on KBr substrate. The electrical properties of the films were measured using evaporated coplanar nickel as the electrode. A semiconductor system was designed to obtain the 1/f noise of pm-Si:H film as well as that of amorphous and microcrystalline silicon films. The results demonstrate that the 1/f noise of pm-Si:H is nearly as low as that of microcrystalline silicon and much lower than that of amorphous silicon. The disorder to order transition mechanism of crystallization was used to analyze the decrease of noise compared with amorphous silicon.     

1/f frequency noise of 2-GHZ high-Q thin-film sapphire resonators

We present experimental results on intrinsic 1/f frequency modulation (FM) noise in high-overtone thin-film sapphire resonators that operate at 2 GHz. The resonators exhibit several high-Q resonant modes approximately 100 kHz apart, which repeat every 13 MHz. A loaded Q of approximately 20000 was estimated from the phase response. The results show that the FM noise of the resonators varied between S_y (10 Hz)=-202 dB relative (rel) to 1/Hz and -210 dB rel to 1/Hz. The equivalent phase modulation (PM) noise of an oscillator using these resonators (assuming a noiseless amplifier) would range from L(10 Hz)=-39 to -47 dBc/Hz     

Nonequilibrium phase transitions and S-shaped current-voltage characteristics in a model semiconductor-metal system

A model of nonequilibrium phase transition in a semiconductor-metal system was considered using a finite-element method. It is shown that, beginning with a certain fraction of the metal component in the heterophase system, the S-shaped current-voltage characteristics exhibit a change: the system features a hysteresis but possesses no singular points.     

Ferromagnetic and antiferromagnetic phase transitions in an itinerant model

The aim of this work is to examine ferromagnetic and antiferromagnetic phase transitions within an itinerant model. Calculating the free energy with the help of the so-called Stoner curves, first-order phase transitions from the paramagnetic to the ferromagnetic state and second-order phase transitions from the paramagnetic to the antiferromagnetic state are found.