Low-frequency Noise Measurements Research Articles

Current Transport and 1/f Noise Characteristics in Ferromagnetic Permalloy/n-type Ge Schottky Contacts

The current transport mechanism in permalloy/n-type Ge Schottky diodes was studied over the temperature range from 200 to 400 K. At temperatures above 250 K, the forward current-voltage (I-V) characteristics of the diode were ideal and obeyed the thermionic emission theory. Below 250 K, however, the recombination process was found to contribute to current transport. Similarly, in reverse bias, the thermionic emission mechanism appeared to dominate current transport at temperatures above 250 K, and the carrier generation mechanism dominated the reverse current below 250 K. A temperature-driven change in the current conduction mechanism from conduction dominated by low-barrier-height patches to conduction dominated by high-barrier-height regions suggests inhomogeneity in the Schottky barrier height. The barrier height inhomogeneity led to deviations in the Richardson constant from its theoretical value at lower temperatures. The room-temperature low-frequency noise measurements taken at different forward biases for the permalloy/n-type Ge Schottky diodes showed a 1/fγ dependence with a tight variation of γ between 1.20 and 1.31. The current dependence of the noise power spectral density exhibited a 1/f noise behavior, indicating the operation of the permalloy/n-type Ge Schottky diodes in the thermionic emission mode.

Defects and Low-Frequency Noise in Irradiated Black Phosphorus MOSFETs With HfO2Gate Dielectrics

We have evaluated radiation-induced charge trapping and low-frequency noise in passivated black phosphorus (BP) MOSFETs with HfO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> gate dielectrics. Thinning the gate dielectric reduces total ionizing dose-induced threshold voltage shifts. The defect-energy distribution estimated from low-frequency noise measurements performed as a function of temperature decreases with increasing energy in as-processed devices. Local maxima in noise magnitude are observed in irradiated devices at activation energies of ~0.2 and ~0.5 eV. Larger defect-related peaks in noise magnitude in the range of 0.35-0.5 eV are observed after biased post-irradiation annealing, and/or vacuum storage of the devices after irradiation and annealing. Density functional theory calculations strongly support significant roles for O vacancies in HfO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> and H+ transport and reactions near the BP/HfO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> interface in the observed radiation response and low-frequency noise.

Low-Frequency Current Fluctuations and Sliding of the Charge Density Waves in Two-Dimensional Materials.

We investigated low-frequency noise in two-dimensional (2D) charge density wave (CDW) systems, 1 T-TaS2 thin films, as they were driven from the nearly commensurate (NC) to incommensurate (IC) CDW phases by voltage and temperature stimuli. This study revealed that noise in 1 T-TaS2 has two pronounced maxima at the bias voltages, which correspond to the onset of CDW sliding and the NC-to-IC phase transition. We observed unusual Lorentzian features and exceptionally strong noise dependence on electric bias and temperature, leading to the conclusion that electronic noise in 2D CDW systems has a unique physical origin different from known fundamental noise types. We argue that noise spectroscopy can serve as a useful tool for understanding electronic transport phenomena in 2D CDW materials characterized by coexistence of different phases and strong pinning.

Simple programmable voltage reference for low frequency noise measurements

The paper presents a circuit design of a low-noise voltage reference based on an electric double-layer capacitor, a microcontroller and a general purpose DAC. A large capacitance value (1F and more) makes it possible to create low-pass filter with a large time constant, effectively reducing low-frequency noise beyond its bandwidth. Choosing the optimum value of the resistor in the RC filter, one can achieve the best ratio between the transient time, the deviation of the output voltage from the set point and the minimum noise cut-off frequency. As experiments have shown, the spectral density of the voltage at a frequency of 1 kHz does not exceed 1.2 nV/√Hz; the maximum deviation of the output voltage from the predetermined does not exceed 1.4 % and depends on the holding time of the previous value. Subsequently, this error is reduced to a constant value and can be compensated.

Out-of-plane interface dipoles and anti-hysteresis in graphene-strontium titanate hybrid transistor

The out-of-plane electric polarization at the surface of SrTiO3 (STO), an archetypal perovskite oxide, may stabilize new electronic states and/or host novel device functionality. This is particularly significant in proximity to atomically thin membranes, such as graphene, although a quantitative understanding of the polarization across graphene–STO interface remains experimentally elusive. Here, we report direct observation and measurement of a large intrinsic out-of-plane polarization at the interface of single-layer graphene and TiO2-terminated STO (100) crystal. Using a unique temperature dependence of anti-hysteretic gate-transfer characteristics in dual-gated graphene-on-STO field-effect transistors, we estimate the polarization to be as large as ≈12 μC cm−2, which is also supported by the density functional theory calculations and low-frequency noise measurements. The anti-hysteretic transfer characteristics is quantitatively shown to arise from an interplay of band bending at the STO surface and electrostatic potential due to interface polarization, which may be a generic feature in hybrid electronic devices from two-dimensional materials and perovskite oxides.

Probing in-plane anisotropy in few-layer ReS2 using low frequency noise measurement

ReS2, a layered two-dimensional material popular for its in-plane anisotropic properties, is emerging as one of the potential candidates for flexible electronics and ultrafast optical applications. It is an n-type semiconducting material having a layer independent bandgap of 1.55 eV. In this paper we have characterized the intrinsic electronic noise level of few-layer ReS2 for the first time. Few-layer ReS2 field effect transistor devices show a 1/f nature of noise for frequency ranging over three orders of magnitude. We have also observed that not only the electrical response of the material is anisotropic; the noise level is also dependent on direction. In fact the noise is found to be more sensitive towards the anisotropy. This fact has been explained by evoking the theory where the Hooge parameter is not a constant quantity, but has a distinct power law dependence on mobility along the two-axes direction. The anisotropy in 1/f noise measurement will pave the way to quantify the anisotropic nature of two-dimensional (2D) materials, which will be helpful for the design of low-noise transistors in future.

Measurement of low-frequency noise during CNC machining and its assessment

The aim of the paper is to point out the necessity to measure noise exposure by means of weighting filter Z, not only weighting filter A, which is prescribed by the standard. The measurement in the paper confirms the various acoustic pressure levels using weighting filter A and weighting filter Z at a low-frequency from 16 Hz to a frequency of 100 Hz. Such measurements suggest that the way in which this noise is evaluated must be adjusted. Due to the risks of exposure to excessive noise, the legislation prescribes regular measurement of permissible noise levels. European legislation and technical standards (e.g. ISO 1996) prescribe “weighting A” in case of such noise. However, this does not respect the energetic effect of sound on the auditory organ, as well as the neuropsychic and cardiovascular system of humans and sensory-motor functions. Experiments and research show that when evaluating low-frequency sounds with strong acoustic energy, the evaluation procedures should be adjusted to the impact of real acoustic energy affecting humans.The noise exposure measurement described in the paper was carried out during production of cars parts that were machined by a CNC machine. The measurement results showed that when weighting filter Z was used, the acoustic pressure levels were higher than those measured by weighting filter A by 22.8 dB. The measured equivalent LZeq values for the given work activity were 73.4 dB(Z) and LAeq was 50.6 dB(A). At low frequencies, this difference was the most pronounced, up to several times higher.

A high speed PE-ALD ZnO Schottky diode rectifier with low interface-state density

Zinc oxide (ZnO) has recently attracted attention for its potential application to high speed electronics. In this work, a high speed Schottky diode rectifier was fabricated based on a ZnO thin film deposited by plasma-enhanced atomic layer deposition and a PtOx Schottky contact deposited by reactive radio-frequency sputtering. The rectifier shows an ideality factor of 1.31, an effective barrier height of 0.79 eV, a rectification ratio of 1.17 × 107, and cut-off frequency as high as 550 MHz. Low frequency noise measurements reveal that the rectifier has a low interface-state density of 5.13 × 1012 cm−2 eV−1, and the noise is dominated by the mechanism of a random walk of electrons at the PtOx/ZnO interface. The work shows that the rectifier can be used for both noise sensitive and high frequency electronics applications.

Оценка качества термоэлектронных катодов сверхвысокочастотных электровакуумных приборов с использованием характеристик низкочастотного шума

It is proposed to estimate the quality of thermionic cathode emitting surface in microwave vacuum tubes from the level and shape of low- frequency noise spectral characteristics. The proposed concept is based on the idea about the noise generation mechanism caused by migrating flow of activating atoms over the surface of weakly emitting defects. The noise is generated due to work function fluctuations caused by a randomly changing number of activating atoms on the defect surface. The cathode emitting surface contains both emission centers with a low work function (the current from them is taken predominantly when the noise is significantly damped by spatial charge) and low-emitting areas with an increased work function, which are in saturated state when there is no spatial charge. The latter ones make the predominant contribution to the noise and perform the role of emission defects. A procedure for preprocessing the measured noise spectral characteristics has been developed, which involves smoothing and averaging by means of median filtering and cubic spline interpolation algorithms. The procedure also includes subsequent decomposition into separate components using the previously modeled base components for defects of different sizes. The decomposition technique has been implemented as a computer program based on a synthesis of spectral characteristics by summation of base components in various combinations. For a group of similar dispenser cathodes made of W-Re sponge impregnated with Ba compounds and coated with a thin Os film, the quantitative content of defects as a function of their dimensions — so-called cathode images — has been determined. The found defect areas increase with the operating time and are proportional to the square of cathode currents. It is shown that a larger defect area obtained from the noise spectral characteristics before long-term tests corresponds to more significant degradation of cathode emission parameters after the test. Thus, the measurement of low-frequency noise and processing the results after comprehensive experimental confirmation on large batches of cathodes can be regarded as a tool for predicting and evaluating the reliability of vacuum tubes.

Influence of LDD Spacers and H+Transport on the Total-Ionizing-Dose Response of 65-nm MOSFETs Irradiated to Ultrahigh Doses

The degradation induced by ultrahigh total ionizing dose in 65-nm MOS transistors is strongly gate-length dependent. The current drive decreases during irradiation, and the threshold voltage often shifts significantly during irradiation and/or high-temperature annealing, depending on transistor polarity, applied field, and irradiation/annealing temperature. Ionization in the spacer oxide and overlying silicon nitride layers above the lightly doped drain extensions leads to charge buildup as well as the ionization and/or release of hydrogen. Charge trapped in the spacer oxide or at its interface modifies the parasitic series resistance, reducing the drive current. The released hydrogen transports as H+ with an activation energy of ~0.92 eV. If the direction of the electric field is suitable, the H+ can reach the gate oxide interface and depassivate Si-H bonds, leading to threshold voltage shifts. Newly created interface traps are most prominent near the source or drain. The resulting transistor responses and defect-energy distributions often vary strongly in space and energy as a result, as demonstrated through current–voltage, charge-pumping, and low-frequency noise measurements.

Reliability Studies on AlGaN/GaN Metal-Insulator-Semiconductor High-Electron-Mobility Transistors with Through-Substrate via Technique and Backside Heat Sink Metal on Silicon-on-Insulator Substrates

AlGaN/GaN metal-insulator-semiconductor high-electron-mobility transistors (MIS-HEMTs) on silicon-on-insulator (SOI) substrates using the through-substrate via (TSV) and back side metal techniques are studies for improving thermal dissipation and device performances. The measured VTH values of the standard (SOI w/o TSV) and MIS-HEMT with TSV (SOI-TSV) devices are −4.1 and −3.9 V. The drain ON/OFF current ratio (ION/IOFF) values of SOI w/o TSV and SOI-TSV devices are 12.96 and 61.62 and the subthreshold swing of these two structures are 248 and 226 mV/dec. The results show that the reduced vertical leakage current in SOI-TSV device exhibited better ION/IOFF ratio and the subthreshold swing than the SOI w/o TSV device. In gate-to-drain current-voltage characteristics, the SOI-TSV devices shows a lower leakage current under the VGS from 0 to −10 V operation than the standard device. Additionally, the reliability and the trapping phenomenon of these two devices were studied using low-frequency noise and pulse measurements. Based on these two structures were processed on the same wafer, the better heat dissipation of SOI-TSV device with Ti/Al back side layer decreases the generation of hot carriers at the reliability stress measurement.

Cyclic Voltammetry Peaks Due to Deep Level Traps in Si Nanowire Array Electrodes

When metal-assisted chemical etching (MACE) is used to increase the effective surface area of Si electrodes for electrochemical capacitors, it is often found that the cyclic voltammetry characteristics contain anodic and cathodic peaks. We link these peaks to the charging–discharging dynamics of deep level traps within the nanowire system. The trap levels are associated with the use of Ag in the MACE process that can leave minute amounts of Ag residue within the nanowire system to interact with the H2O layer surrounding the nanowires in a room temperature ionic liquid. The influence of the traps can be removed by shifting the Fermi level away from the trap levels via spin-on doping. These results in lower capacitance values but improved charge–discharge cycling behavior. Low-frequency noise measurements proof the presence or absence of these deep level traps.

Noise Properties of Graphene-Polymer Thick-Film Resistors

AbstractGraphene is a very promising material for potential applications in many fields. Since manufacturing technologies of graphene are still at the developing stage, low-frequency noise measurements as a tool for evaluating their quality is proposed. In this work, noise properties of polymer thick-film resistors with graphene nano-platelets as a functional phase are reported. The measurements were carried out in room temperature. 1/f noise caused by resistance fluctuations has been found to be the main component in the specimens. The parameter values describing noise intensity of the polymer thick-film specimens have been calculated and compared with the values obtained for other thick-film resistors and layers used in microelectronics. The studied polymer thick-film specimens exhibit rather poor noise properties, especially for the layers with a low content of the functional phase.

Measurement of Noise in Supercapacitors

AbstractA developed method and measurement setup for measurement of noise generated in a supercapacitor is presented. The requirements for noise data recording are considered and correlated with working modes of supercapacitors. An example of results of low-frequency noise measurements in commercially available supercapacitors are presented. The ability of flicker noise measurements suggests that they can be used to assess quality of tested supercapacitors.

Low-Frequency Noise in III–V Nanowire TFETs and MOSFETs

We present a detailed analysis of low-frequency noise (LFN) measurements in vertical III-V nanowire tunnel field-effect transistors (TFETs), which help to understand the limiting factors of TFET operation. A comparison with LFN in vertical metal-oxide semiconductor field-effect transistors with the same channel material and gate oxide shows that the LFN in these TFETs is dominated by the gate oxide properties, which allowed us to optimize the TFET tunnel junction without deteriorating the noise performance. By carefully selecting the TFET heterostructure materials, we reduced the inverse subthreshold slope well below 60 mV/decade for a constant LFN level.

RF Performance of &lt;italic&gt;In Situ&lt;/italic&gt; SiN&lt;italic&gt;x&lt;/italic&gt;Gate Dielectric AlGaN/GaN MISHEMT on 6-in Silicon-on-Insulator Substrate

A high power-added efficiency and low dynamic on-resistance ( $R_{ \mathrm{\scriptscriptstyle ON}})$ AlGaN/GaN metal–insulator–semiconductor high-electron mobility transistor (MISHEMT) with in situ SiN x insulator design was demonstrated on 150-mm silicon-on-insulator (SOI) substrate. Compared to traditional high-resistivity Si substrate, SiN x /AlGaN/GaN MISHEMT grown on the SOI 5- $\mu \text{m}$ -thick Si active layer performed better tensile stress relaxation and surface flatness. Based on Hall measurement results, electron mobility and the sheet charge density on SOI substrate were improved simultaneously owing to a lower-defect density which is also proofed by pulse measurement and low-frequency noise measurement. Due to the low-feedback substrate capacitance, the bandwidth, and the linearity were also improved simultaneously by SOI substrate design.

Investigation on the Conduction Mechanisms in Metal-Base Vertical Organic Transistors by DC and LF-Noise Measurements

Vertical organic transistors are a promising candidate to overcome the scaling limits of conventional horizontal organic field-effect devices. In this paper, based on the results of direct current (dc) and low-frequency noise (LFN) measurements, we propose a picture for the carrier transport in metal-base organic transistors in which transmission across the base is due to the combined action of both hot-carriers (HCs) and high-conduction paths (pores) in the metal base. Investigated devices employ pentacene and copper phthalocyanine as active layers for the emitter and collector regions, and a bilayer consisting of Au/MoO3 as injecting electrode. The dc analysis highlights that the charge transport in the investigated devices is due to drift diffusion of the emitter-injected carriers in the highest occupied molecular orbital (HOMO) band and is dominated by HC injection, although conduction via pores increases and becomes not negligible at high base–emitter fields. The LFN analysis highlights the presence of two dominant and uncorrelated 1/f current noise sources, one located between base and emitter, due to the fluctuations of the not-transmitted HC current, and a second source located between collector and emitter, due to the fluctuations of the transmitted HC current and/or to the fluctuations of the current through the pores in the metallic base.

Mobile Adaptable Measuring Instrument of Low-Frequency Noise Characteristics in Diagnostics of Vacuum Tube Devices

Mobile measuring equipment adapted for measurements of low-frequency noise of vacuum tubes with a broad range of impedance characteristics has been developed. Control software making it possible to measure and process the obtained results in automatic mode has been created. The capability of determining the diagnostic parameters of thermionic cathodes of vacuum tubes is shown.

On current transients in MoS2 Field Effect Transistors

We present an experimental investigation of slow transients in the gate and drain currents of MoS2-based transistors. We focus on the measurement of both the gate and drain currents and, from the comparative analysis of the current transients, we conclude that there are at least two independent trapping mechanisms: trapping of charges in the silicon oxide substrate, occurring with time constants of the order of tens of seconds and involving charge motion orthogonal to the MoS2 sheet, and trapping at the channel surface, which occurs with much longer time constants, in particular when the device is in a vacuum. We observe that the presence of such slow phenomena makes it very difficult to perform reliable low-frequency noise measurements, requiring a stable and repeatable steady-state bias point condition, and may explain the sometimes contradictory results that can be found in the literature about the dependence of the flicker noise power spectral density on gate bias.

Improved reverse recovery characteristics of inAlN/GaN schottky barrier diode using a SOI substrate

The low-frequency noise (LFN) and reverse recovery charge characteristics of a six-inch InAlN/AlN/GaN Schottky barrier diode (SBD) on the Si-on-insulator (SOI) substrate were demonstrated and investigated for the first time. Raman spectroscopy indicated that using SOI wafers lowered epitaxial stress. According to the DC and LFN measurements at temperatures ranging from 300 to 450 K, the InAlN/GaN SBD on the SOI substrate showed improved forward and reverse currents and achieved a lower reverse recovery charge, compared with a conventional device.