Current Noise Spectra Research Articles

Origin of Low-Frequency Noise in Triple-Gate Junctionless n-MOSFETs

The low-frequency noise in triple-gate junctionless n-MOSFETs, with channel lengths varying from 95 to 25 nm and operating in the bulk and accumulation modes, is investigated by measurements in the frequency and time domains. The experimental drain current noise spectra present $1/{f}$ and Lorentzian-type behavior components. The noise spectra in the time domain reveal that the Lorentzian-type behavior components are due to the capture and emission processes of carriers at discrete gate insulator traps, resulting in random telegraph noise (RTN). The $1/{f}$ behavior can be described by the carrier number with the correlated mobility fluctuations model. In the below-threshold region, the conducting channel is isolated from the interface by depletion region. In the above-threshold region (bulk conduction mode), the histograms of the time-domain data show multilevel switching events, from which one or more individual traps can be distinguished. The extracted time constants of two-level RTN signals indicate the interaction of a single trap either with the channel or with both channel and gate. The relative RTN amplitude is described with the carrier number with the mobility correlated fluctuations physics-based model or with the “hole in the inversion layer” stochastic simulation-based model, enabling estimation of the flat-band voltage fluctuation caused by the RTN.

Finite-frequency noise of interacting single-electron emitters: Spectroscopy with higher noise harmonics

We derive the symmetrized current-noise spectrum of a quantum dot, which is weakly tunnel-coupled to an electron reservoir and driven by a slow time-dependent gate voltage. This setup can be operated as an on-demand emitter of single electrons into a mesoscopic conductor. By extending a real-time diagrammatic technique which is perturbative in the tunnel coupling, we obtain the time-resolved finite-frequency noise as well as its decomposition into noise harmonics in the presence of both strong Coulomb interaction and slow time-dependent driving. We investigate the noise over a large range of frequencies and point out where the interplay of Coulomb interaction and driving leads to unique signatures in finite-frequency noise spectra, in particular in the first harmonic. Besides that, we employ the first noise harmonic as a spectroscopic tool to access individual fluctuation processes. We discuss how the inverse noise frequency sets a time scale for fluctuations, which competes with time scales of the quantum-dot relaxation dynamics as well as the driving.

Small- and Large-Signal Analyses of Different Low-Pressure-Chemical-Vapor-Deposition SiN x Passivations for Microwave GaN HEMTs

Three types of SiN x passivation for microwave AlGaN/GaN HEMTs were deposited with low-pressure chemical vapor deposition under different deposition conditions, resulting in different silicon contents. The performance of the HEMTs is comprehensively investigated and compared. Both small- and large-signal analyses, such as generation–recombination (G–R) trap analysis, low-frequency noise characterization, and load–pull measurement, are indispensable to evaluate the effectiveness of a surface passivation. A Si-rich SiN x passivation shows excess G–R centers, whereas a Si-poor SiN x passivation exhibits significant current slump (30%). A bilayer SiN x passivation successfully shows not only a small current slump (~9.7%) but also a suppressed G–R trapping/detrapping process. Moreover, the bilayer passivation demonstrates almost 2 orders of magnitude lower gate current noise spectra compared with the single-layer Si-rich SiN x passivation. The capacitance-voltage measurements reveal that the Si-rich SiN x layer removes the deep-level traps at the AlGaN/SiN x interface. Considering both small- and large-signal operations, it is concluded that the bilayer SiN x passivation is a suitable and versatile candidate for microwave GaN devices.

Analytical derivation of charge relaxation time distribution in transistor from current noise spectrum using inverse integral transformation method

An analytical technique is proposed to reveal the relaxation time distribution of dynamic charge events using the current noise spectrum of a transistor, by applying an inverse integral transformation to the McWhorter model. In the proposed method, the continuous relaxation-time distribution function G(τ) can be analytically derived from the noise spectra S(ω) without a spectrum deconvolution. The feasibility of the proposed method is demonstrated by characterizing the charge dynamics of tetraphenylporphyrin molecules dispersed on the surface of a GaAs-based nanowire field-effect transistor. Our analysis successfully verified the time constant of the molecule-related dynamic charge events and effects of photo-excitation.

Modeling and characterization of the low frequency noise behavior for amorphous InGaZnO thin film transistors in the subthreshold region

An analytical model of the low-frequency noise (LFN) for amorphous InGaZnO (a-IGZO) thin film transistors (TFTs) in the subthreshold region is developed. For a-IGZO TFTs, relations between the device noise and the subgap defects are characterized based on the dominant multiple trapping and release (MTR) mechanism. The LFN is considered to be contributed from trapping/detrapping of carriers both into the border traps and the subgap density of states (DOS). It is revealed that the LFN behavior of a-IGZO TFTs in the subthreshold region is significantly influenced by the distribution of tail states, where MTR process prevails. The 1/f α (with α < 1) spectrum of the drain current noise is also related to the characteristic temperature of the tail states. The new method is introduced to calculate the LFN of devices by extracting the LFN-related DOS parameters from the current-voltage characteristics.

Performance Characterization of Random Pulse Width Modulation Algorithms in Industrial and Commercial Adjustable-Speed Drives

One of the problems of the pulse-width-modulation (PWM)-controlled ac machines is the acoustic noise that could become unacceptable when used in sensitive environments. Random PWM (RPWM) in industrial and commercial adjustable-speed drives (ASD) results in the partial transfer of power from the discrete spectrum (narrowband noise) of the output voltage to the continuous spectrum (wideband noise), with advantageous effects on reducing the acoustic noise in the motor drive system. In this paper, the theoretical power spectrum analysis as the basis for RPWM is presented. Five state-of-the-art RPWM strategies, their voltage, current, and acoustic noise spectra characteristics are quantitatively evaluated. The PWM schemes and theoretical analysis are validated through a 2.2-kW 380-V 50-Hz ASD induction machine experimental setup. The results provide valuable data for practicing engineering community to choose the best option in real-world applications.

Tunneling current noise spectra of biased impurity with a phonon mode

We report the results of theoretical investigations of the tunneling current noise spectra through a single-level impurity both in the presence and in the absence of electron–phonon interaction based on the nonequilibrium Green’s functions formalism. We show that due to the quantum nature of tunneling, the Fano factor is dramatically different from the Poisson limit both in the presence and in the absence of inelastic processes. The results are demonstrated to be sensitive to the tunneling contact parameters.

Influence on Noise Performance of GaN HEMTs With In Situ and Low-Pressure-Chemical-Vapor-Deposition SiN x Passivation

High-frequency and low-frequency noise (LFN) performance of GaN high electron-mobility transistors (HEMTs), passivated with SiN x deposited by either $in~situ$ or low-pressure-chemical-vapor-deposition (LPCVD), are compared. From 8–26 GHz, the LPCVD sample has a lower minimum noise figure (1 dB at 8 GHz) because of lower power spectral density of noise sources and less transconductance ( $g_{m})$ dispersion. The LPCVD and the $in~situ$ SiN x passivated HEMTs exhibit similar LFN in the 1 Hz–100 kHz range (drain current noise spectra $\sim 10^{-17}~\text{A}^{2}$ /Hz at 100 kHz). Nevertheless, LPCVD should be a preferred choice for voltage-controlled oscillator (VCO) applications, since it is capable of suppressing current collapse more effectively, which results in a higher output power and, therefore, a lower phase noise. Furthermore, the low current collapse, low LFN, and minimum noise figure makes the LPCVD SiN x passivation a promising candidate for multifunctional monolithic microwave integrated circuits, including power amplifiers, low-noise amplifier, switches, mixers, and VCOs.

Low-Frequency Noise in Advanced SiGe:C HBTs—Part I: Analysis

In this paper, we present extensive characterization of low-frequency noise in advanced silicon germanium heterojunction bipolar transistors. We demonstrate the extraction methodology of base and collector noise spectral densities for a wide range of transistor geometries. In addition to 1/ $f$ noise, generation–recombination (G–R) mechanisms are observed at low bias in the base current noise. Their existence is confirmed by Random Telegraph Signal (RTS) noise measurements. 1/ $f$ and G–R components are extracted from the base current noise spectra and their bias dependencies are studied. Finally, base current noise spectral densities measured at the same base current density in different geometries are compared to study the individual contribution of 1/ $f$ noise from the periphery as well as the intrinsic device. Part II of this paper will discuss the modeling aspects and noise correlation.

Biased impurity tunneling current emission spectrum in the presence of quasi-particle interaction

Abstract We performed theoretical investigations of the tunneling current noise spectra through single-level impurity in the presence of quasi-particle (electron-phonon) interaction by means of the non-equilibrium Green function formalism. We demonstrated a fundamental link between quantum noise in tunneling contact and light emission processes. We calculated tunneling current noise spectra through a single level impurity atom both in the presence and in the absence of quasi-particle interaction for a finite bias voltage and identified it as a source of experimentally observed light emission from bias STM contacts. The results turn out to be sensitive to the tunneling contact parameters. Our findings provide important insight into the nature of non-equilibrium electronic transport in tunneling junctions with quasi-particle interaction.

Dissipation equation of motion approach to open quantum systems

This paper presents a comprehensive account of the dissipaton-equation-of-motion (DEOM) theory for open quantum systems. This newly developed theory treats not only the quantum dissipative systems of primary interest, but also the hybrid environment dynamics that are also experimentally measurable. Despite the fact that DEOM recovers the celebrated hierarchical-equations-of-motion (HEOM) formalism, these two approaches have some fundamental differences. To show these differences, we also scrutinize the HEOM construction via its root at the influence functional path integral formalism. We conclude that many unique features of DEOM are beyond the reach of the HEOM framework. The new DEOM approach renders a statistical quasi-particle picture to account for the environment, which can be either bosonic or fermionic. The review covers the DEOM construction, the physical meanings of dynamical variables, the underlying theorems and dissipaton algebra, and recent numerical advancements for efficient DEOM evaluations of various problems. We also address the issue of high-order many-dissipaton truncations with respect to the invariance principle of quantum mechanics of Schrodinger versus Heisenberg prescriptions. DEOM serves as a universal tool for characterizing of stationary and dynamic properties of system-and-bath interferences, as highlighted with its real-time evaluation of both linear and nonlinear current noise spectra of nonequilibrium electronic transport.

Plasmonic noise of field-effect transistors operating at terahertz frequencies

We analyze electronic noise in field-effect transistors associated with plasma waves in the terahertz frequency domain by using a numerical approach based on the coupled hydrodynamic and Poisson equations. The current and voltage noise spectra, calculated by means of the transfer impedance method, exhibit a series of peaks associated with two- and three-dimensional plasma resonances. The two-dimensional plasma peaks have been found to depend on the channel length including gated and ungated regions. Under asymmetric boundary conditions, electrical instabilities characterized by terahertz oscillations of the drain voltage and gate current can be reached at sufficiently high values of the total drain current. A resonant enhancement of the plasma peaks in the noise spectra has been found to be a precursor of the instability onset. Through a spatial analysis of the local contributions we have shown that the main contribution to the total noise at frequencies near the plasma resonance comes from the ungated n-region placed between the source and the gate contacts.

A Modified 1/ Noise Model for MOSFETs With Ultra-Thin Gate Oxide

A modified 1/ $f$ noise model has been proposed for MOSFETs with an ultra-thin gate oxide layer. It is revealed that as the gate length $L$ deceases, the normalized drain current noise spectra density also decreases, which does not coincide with the regular 1/ $f$ noise theory. It is found that the trap-assisted gate leakage affects the drain current 1/ $f$ noise, and for the first time, it is demonstrated that the equivalent oxide trap density, the free carrier density, as well as $L$ determine the 1/ $f$ noise. A modified quantitative model is then proposed, which can well predict the 1/ $f$ noise.

Investigation of local tunneling current noise spectra on the silicon crystal surfaces by means of STM/STS

We report on a careful analysis of the local tunneling conductivity by means of ultra-high vacuum scanning tunneling microscopy/spectroscopy (STM/STS) technique in the vicinity of low-dimensional structures on the Si(111)–(7 × 7) and Si(110)–(16 × 2) surfaces. The power-law exponent α of low-frequency tunneling current noise spectra is investigated for different values of the tunneling contact parameters: relaxation rates, the localized state coupling, and the tunneling barrier width and height.

Current noise spectra and mechanisms with dissipaton equation of motion theory.

Based on the Yan's dissipaton equation of motion (DEOM) theory [J. Chem. Phys. 140, 054105 (2014)], we investigate the characteristic features of current noise spectrum in several typical transport regimes of a single-impurity Anderson model. Many well-known features such as Kondo features are correctly recovered by our DEOM calculations. More importantly, it is revealed that the intrinsic electron cotunneling process is responsible for the characteristic signature of current noise at anti-Stokes frequency. We also identify completely destructive interference in the noise spectra of noninteracting systems with two degenerate transport channels.

Description of the Spectrum of Natural Noise in Semiconductor Diodes Based on the Modified Van Der Ziel Relation

UDC 621.391.822 In this work, we study the spectrum SiD of natural (thermal and shot) current noise of the p-n junction and the Schottky barrier in the case where their current-voltage characteristic has a nonideality coefficient η exceeding unity. The results obtained with the help of a special experimental setup are presented and explained using an equivalent scheme, which takes into account the presence of the series resistance of the diode base and contacts, as well as the possibility of existence of the leakage current. It is theoretically proven and experimentally confirmed that the van der Ziel relation SiD =2 q (ID +2 Is), which is used for calculating the current-noise spectrum of an “ideal” junction with η =1 , cannot be used for η> 1 (here, q is the elementary charge, ID is the current across the junction, and Is is the junction saturation current). The previously obtained results are generalized using the Gupta theorem for the thermal-noise spectrum in the nonlinear resistive systems and are confirmed experimentally. It is found that the noise-current spectrum is given by the formula SiD =( 2 q/η )( ID +2 Is), which is a modification of the van der Ziel relation for the case of an arbitrary value of the nonideality coefficient. The obtained formula for SiD is experimentally tested by measuring the noise spectrum of the δ-doped Schottky diode, which is in thermodynamic equilibrium with the surrounding medium.

Electroluminescence and multiphoton effects in a resonator driven by a tunnel junction

We study a transmission line resonator which is driven by electrons tunneling through a voltage-biased tunnel junction. Using the Born-Markovian quantum master equation in the polaron basis we investigate the nonequilibrium photon state and emission spectrum of the resonator as well as properties of the transport current across the tunnel junction and its noise spectrum. The electroluminescence is optimized, with maximum peak height and narrow linewidth, when the back-action of the tunnel junction on the resonator and the damping of the resonator are similar in strength. For strong coupling between the resonator and tunnel junction, multiphoton effects create signatures in the transport current and current noise spectrum.

Phonon effects on the current noise spectra and the ac conductance of a single molecular junction

By using nonequilibrium Green’s functions and the equation of motion method, we formulate a self-consistent field theory for the electron transport through a single-molecule junction (SMJ) coupled with a vibrational mode. We show that the nonequilibrium dynamics of the phonons in a strong electron–phonon coupling regime can be taken into account appropriately in this self-consistent perturbation theory, and the self-energy of the phonons is connected with the current fluctuations in the molecular junction. We calculate the finite-frequency nonsymmetrized noise spectra and the ac conductance, which reveal a wealth of inelastic electron tunneling characteristics on the absorption and emission properties of this SMJ. In the presence of a finite bias voltage and the electron tunneling current, the vibration mode of the molecular junction is heated and driven to an unequilibrated state. The influences of unequilibrated phonons on the current and the noise spectra are investigated.

Noise Phenomena Caused by Reversible Adsorption in Nanoscale Electrochemical Devices

We theoretically investigate reversible adsorption in electrochemical devices on a molecular level. To this end, a computational framework is introduced, which is based on 3D random walks including probabilities for adsorption and desorption events at surfaces. We demonstrate that this approach can be used to investigate adsorption phenomena in electrochemical sensors by analyzing experimental noise spectra of a nanofluidic redox cycling device. The evaluation of simulated and experimental results reveals an upper limit for the average adsorption time of ferrocene dimethanol of ∼200 μs. We apply our model to predict current noise spectra of further electrochemical experiments based on interdigitated arrays and scanning electrochemical microscopy. Since the spectra strongly depend on the molecular adsorption characteristics of the detected analyte, we can suggest key indicators of adsorption phenomena in noise spectroscopy depending on the geometric aspect of the experimental setup.

Current Noise and AC Response of a Back-Gated Single-Molecule Junction

Current noise and ac response properties of single-molecule junctions (SMJs) are essential for their potential application as nanoscale electron devices. We first study I-V characteristics of electronic transport through a back-gated benzene-type SMJ based on the nonequilibrium Green's function formalism within a tight-binding model, and then present analytical expressions and numerical calculations for current noises and ac conductances of the SMJ. We show that the noise power density in the high-frequency region is independent of the applied bias voltage, and will be significantly suppressed and have dip structures at the frequencies where electron transitions from the occupied molecular states to the unoccupied ones are excited. It is found that both the bias voltage and the back-gate voltage can affect current noise spectra and ac conductances drastically in the low-frequency region. The low-frequency part of the ac conductance can be enhanced by applying a bias voltage, but an opposite behavior with suppression of conductances is observed for the system without the particle-hole symmetry. AC conductances for the source and the drain leads also show distinct characteristics for this SMJ system. It is expected that our results will provide some bases for the ac application of SMJ nanodevices.