Defect Profiles Research Articles

An Opening Profile Recognition Method for Magnetic Flux Leakage Signals of Defect

The defect opening profile recognition is of great concern in the magnetic flux leakage (MFL) measurement technique. The detected spatial MFL signal has three components: horizontal, vertical, and normal components. Horizontal and normal component signals are commonly used to estimate the defect profile, while the vertical component has always been neglected. With the development of the high resolution and the 3-D MFL testing techniques, the vertical component signal is becoming more available. This paper analyzes the essential right-angle features of the vertical component signal, which is useful for the defect opening profile recognition. After obtaining the initial profile from the horizontal or normal component, the types of the right angle is identified from the vertical component, and the opening profile is further optimized based on these right-angle features. The opening profile recognition method is put forward in this paper to improve the accuracy of the recognition result of the defect. Both simulation and experimental tests are conducted to verify the good performance of the proposed method. Compared with the opening profiles recognized merely by the horizontal component signal, the proposed method shows better recognition results, which also validates that the vertical component signal can also be a useful information for the defect estimation.

On the Impact of the Gate Work-Function Metal on the Charge Trapping Component of NBTI and PBTI

We investigate bias temperature instability (BTI) charge trapping trends in high-k metal gate (HKMG) stacks with a variety of work function metals (WFMs). Most BTI models suggest charge trapping in oxide defects is modulated by the applied oxide electric field, which controls the energy barrier for the capture process, irrespective of the gate work function. However, experimental data on capacitors show enhanced or reduced charge trapping at a constant oxide electric field for different WFM stacks. We ascribe this to a different chemical interaction of the metals with the dielectric, which yields different defect profiles depending on the process thermal budget, and not to the gate work function per se. This observation is confirmed by comparing BTI degradation in nMOS and pMOS replacement gate planar transistors with three selected WFM stacks (representative of high-, standard-, and low-Vth device flavors), and two different process thermal budgets. Furthermore, by employing the imec/T.U. Wien physics-based BTI simulation framework “Comphy,” we also show that, on top of the unavoidable chemical interaction of different metals with the underlying SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /HfO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> dielectric stack, different gate work functions within a typical range of relevance (4.35-4.75 eV) can yield a different charge state of the deep high-k defects, and can therefore have an impact on charge trapping kinetics during BTI stress, particularly in nMOSFETs.

Effect of boundary conditions on reduction during early stage flash sintering of YSZ

The onset of flash sintering is generally considered to be predominantly a function of the conductivity of a given ceramic, the furnace temperature, and the electric field. However, the evolution of the point defect profiles in ionic conductors such as yttria-stabilized zirconia (YSZ) can complicate the picture of homogeneous Joule heating and thermal runaway during DC flash sintering. Here, 8 mol% YSZ pellets were partially flash sintered under a DC bias using various current densities and hold times. The electrode geometry was varied to modulate the oxygen ion flux available to the cathode to compare the effects on the resulting oxygen vacancy inhomogeneity. The contribution from fundamental and experimental factors to the cathodic reduction reaction is also discussed, such as interface reaction kinetics and sample geometry. Local reduction of the ceramic was inevitably observed under all current densities and the resulting microstructural inhomogeneity was explained as the result of a transient conductivity asymmetry. This asymmetry was the result of the enhanced electronic conductivity in the cathode region to a value significantly greater than the ionic conductivity of near-stoichiometric YSZ. The link between the local conductivity, voltage and Joule heating is mathematically demonstrated to result in an asymmetric heating profile.

Моделирование областей разупорядочения в процессе радиационного дефектообразования

This article discusses the model of regions of disordering that are formed as a result of the separation of Frenkel pairs, taking into account the neutral and charged state of the pair. The probability of separation depends on the temperature and the position of the Fermi level in the band gap, therefore, the concentration of primary radiation defects also depends on the temperature and concentrations of donors, acceptors. The depth distribution profiles of primary radiation defects created by low-energy protons in silicon and the dependence of the parameters of the disordering regions on the proton energy are calculated. It is shown that the maximum of the distribution of the disordering regions created by protons is always spatially separated from the maxima of the interstitial silicon distribution, vacancies and divacancies, which allows changing the surface and volume properties of semiconductor structures in various ways. The results obtained are used to predict the characteristics of semiconductor devices operating under conditions of radiation exposure.

Unraveling the Charge State of Oxygen Vacancies in ZrO2–x on the Basis of Synergistic Computational and Experimental Evidence

The functional properties of metal oxide semiconductors depend on intrinsic and extrinsic defects. The population of intrinsic defects is strongly affected by the synthesis method and subsequent treatments of the material, while extrinsic defects can originate from suitable doping. Stoichiometric ZrO2 is a nonreducible oxide with a large band gap. Therefore, controlling and modulating its defect profile to induce energy states in the band gap is the sole possibility to make it a photocatalyst responsive to visible light. We report a method, based on low temperature sol–gel synthesis coupled with treatments performed in mild conditions, to obtain undoped visible light-responsive ZrO2–x. The electronic structure of these materials is interpreted in relation to their oxygen vacancy defect population. On the basis of a wide set of experimental measurements (X-ray photoelectron, steady-state and time-resolved photoluminescence, electron paramagnetic resonance, and UV–visible diffuse reflectance spectroscopy) a...

Arsenic-ion implantation-induced defects in HgCdTe films studied with Hall-effect measurements and mobility spectrum analysis

The Hall-effect/electrical conductivity measurements and mobility spectrum analysis (MSA) have been used for the study of the profiles of different electron species and corresponding defects induced in a HgCdTe film by implantation of arsenic ions. Two specific donor defects were revealed as a result of extracting parameters of different carrier species found with MSA. Identification of the defects was performed with the use of the data acquired with transmission electron microscopy and the literature data on Rutherford backscattering. It was found that low-mobility (∼5000 cm2/(V·s)) electrons originated from donor centers formed when mercury interstitials were captured by implantation-induced dislocation loops, while middle-mobility (∼20,000 cm2/(V·s)) electrons were due to donor centers formed when the interstitials were captured by quasi-point radiation defects. For comparison, profiling was also performed with the single-field differential Hall-effect measurements. The results of the study suggest that only MSA-assisted carrier profiling is capable of retrieving actual defect profiles in ion-implanted HgCdTe.

Nanoscale magnetization reversal by electric field-induced ion migration

Abstract

Study of damage in binary Fe85Cr15 alloys irradiated by ions and the effect of an external magnetic field during irradiation

Understanding radiation-induced damage in iron-chromium alloys is critical for the use of advanced steels in future fusion reactors. However, the role of the strong magnetic fields present in such magnetically confined plasma devices on material damage, though considered important, has not been thoroughly explored to date. In this work, irradiation experiments of Fe85Cr15 alloy (15% Cr content) by heavy (Fe+) and light (He+) ions have been carried out in order to characterize the damage and, additionally, the influence of an external magnetic field (B = 0.4 T) has been taken into account. The analysis of the data has been done with different techniques, the distribution of the Cr and/or vacancies around probe nuclei has been explored by Mössbauer spectroscopy and the vacancy profile by Slow Positron Annihilation Spectroscopy (SPAS). Comparison between samples irradiated by He+ and Fe+, in absence of B, reveals significant differences in the average hyperfine magnetic field (<ΔH> = 0.8 T). This can be attributed to changes in the local environment around the probe nuclei (57Fe) where either vacancies or the Cr distribution play a role. From depth-profiling by SPAS in Fe+ irradiated samples, a large concentration of vacancy-type defects is found with a profile that extends deeper than that predicted by computer simulations. Furthermore, sequential irradiation by Fe+ and He+ ions indicates that the He atoms tend to fill the vacancy clusters just in the depth where the He+ is implanted. On the other hand, small but significant differences in vacancy-type defect profiles are found between the samples irradiated both in the presence and absence of a magnetic field (B = 0.4 T) both independently of single and sequential irradiation. Detailed Mössbauer spectroscopy and SPAS analysis seem to point out that external magnetic fields could be a non-negligible parameter in the material damage due to ion irradiation.

Bio-realistic synaptic characteristics in the cone-shaped ZnO memristive device

We demonstrate inherent biorealistic synaptic plasticity functions in the Pt/n-ZnO/SiO2–x/Pt heterostructures, where the n-ZnO semiconductor is geometrically cone-shaped in the size of a few nanometers. The synaptic functions were achieved within a two-terminal, electroforming-free, and low-power rectifying diode-like resistive switching device. The important rate-dependent synaptic functions, such as the nonlinear transient conduction behavior, short- and long-term plasticity, paired-pulse facilitation, spike-rate-dependent plasticity and sliding threshold effect, were investigated in a single device. These characteristics closely mimic the memory and learning functions of those in biosynapses, where frequency-dependent identical spiking operations are mostly taking place, and we emulate these characteristics in the “Learning-Forgetting-Relearning” synaptic behavior. The switching dynamics in the cone-shaped n-ZnO semiconductor are correlated with the transport mechanism along the grain boundaries of the charged ion species, namely, oxygen vacancies and charged oxygen. The diffusion and generation/recombination of these defects have specific time scales of self-decay by virtue of the asymmetric profile of the n-ZnO cone defects. Finally, the essential biorealistic synaptic plasticity functions were discovered for the perspectives of dynamic/adaptive electronic synapse implementations in hardware-based neuromorphic computing.

Fast reconstruction of 3-D defect profile from MFL signals using key physics-based parameters and SVM

Fast reconstruction of three-dimensional (3-D) defect profile from three-axis magnetic flux leakage (MFL) signals is important to the pipeline inline inspection (ILI) in the oil and gas industry. Traditional methods require the processing of a large amount of raw input and output data, which poses significant challenges in balancing the inspection efficiency, i.e. sensing and data processing speed, and the ILI accuracy and robustness. Here, a novel fast reconstruction framework combining key physics-based parameters and data-driven machine learning algorithms is proposed. Geometric parameters based rational Bézier curve (RBC) model is proposed to generate the 3-D defect profile, while local and global feature parameters are determined using a nonlinear least square (NLS) approach from the three-axis MFL signals. These physics-based geometric and feature parameters are then correlated through a least-square support vector machine (LS-SVM). Meanwhile, a pipeline inspection gauge (PIG) is developed to measure the three-axis MFL signals for evaluating the reconstruction performance through field testing. Both simulation and experimental results demonstrate that the proposed method's accuracy, robustness and computation speed have been improved significantly comparing with other existing methods.

TDDB Mechanism in a-Si/TiO2 Nonfilamentary RRAM Device

Mechanisms of time-dependent dielectric breakdown (TDDB) in nonfilamentary a-Si/TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> RRAM cell [a-vacancy modulated conductive oxide (VMCO)] have been examined in this paper, including defects generation in the grain boundary, defects clustering, and different defects generation rates in a-Si and TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> layers. The unique feature of a bimodal Weibull distribution at low-resistance state (LRS) and a single shallow slope distribution at high-resistance state (HRS) cannot be explained by the above mechanisms. By using a combination of constant voltage stress, time-to-breakdown Weibull distribution, and random telegraph noise (RTN)-based defect profiling in devices of various sizes, layer thicknesses, and processes, it is revealed that the defect profile is modulated when switching between HRS and LRS and the correlation of defect profile modulation with local defect generation rate can explain the difference in Weibull distributions at HRS and LRS. The transition from bimodal distribution at LRS to a single-steep slope with thinner a-Si layer, and the good area scaling of Weibull distribution at HRS but not at LRS, can also be explained. The critical layers affecting the TDDB in a-VMCO are identified, providing useful guidance for device performance improvement.

Образование дефектов в структурах GaAs с непокрытой и покрытой пленкой AlN поверхностями при имплантации ионов азота и последующем отжиге

AbstractThe concentration profiles of defects produced in structures upon the implantation of nitrogen ions into GaAs epitaxial layers with an uncovered surface and that covered with an AlN film and subsequent annealing are studied. The ion energies and the implantation doses are chosen so that the nitrogen-atom concentration profiles coincided in structures of both types. Rutherford proton backscattering spectra are measured in the random and channeling modes, and the concentration profiles of point defects formed are calculated for the samples under study. It is found that the implantation of nitrogen ions introduces nearly the same number of point defects into structures of both types, and the formation of an AlN film by ion-plasma sputtering is accompanied by the formation of an additional number of defects. However, the annealing of structures of both types leads to nearly the same concentrations of residual defects.

Characterization of the distribution of defects introduced by plasma exposure in Si substrate

Defects in a silicon (Si) substrate induced by plasma exposure—plasma-induced damage (PID)—were investigated using various techniques. The authors performed a comprehensive characterization of plasma induced damages, which will be indispensable for suppressing PID, by precisely assigning the density profile of defects in the region to ∼1016 cm−3. In this study, the Si substrate was damaged using an electron cyclotron resonance plasma system. Cathodoluminescence analysis was used to detect the defects in the damaged Si substrates. The thickness of the damaged layer in the Si substrates was determined to be approximately 1–2 nm by transmission electron microscopy and spectroscopic ellipsometry, while time-of-flight secondary ion mass spectrometry identified the presence of interstitial atoms to a depth of ∼20 nm. Positron annihilation spectroscopy showed that the structural changes related to vacancies interacting with C and F atoms were distributed from the substrate surface to a depth of approximately 130 nm. The authors further verified this finding by a technique using the PID-enhanced dechanneling of As atoms implanted with a projection range of 10 nm. After plasma exposure, the difference between the plasma-damaged and the nondamaged samples in the injected As profiles was identified to a depth of ∼130 nm with a density of ∼1016 cm−3. The comprehensive defect profiling performed in this study provides key guidelines for the introduction mechanism of defects in plasma exposed Si before designing future electronic devices.

Enhanced electron transfer properties of NiO thin film for the efficient detection of urea

Ur/NiO matrix is used efficiently for the detection of Urea. NiO thin film is deposited using rf magnetron sputtering. Variation in processing pressure (10–40 mT) and growth temperature (room temperature to 500 °C) during film deposition alter its defect profile, thus tailoring the charge transfer characteristics. The studies reveal a relationship between biosensing characteristics with various properties of NiO matrix (structural, electrical etc.). The Ur/NiO/ITO/glass biosensor demonstrate very high sensitivity (66.7 μA/(mM)) with rapid time of response (5 s) and good linearity over a wide range of urea concentration (0.83–16.65 Mm). Lower Michaelis–Menten constant value (Km = 0.34 mM) ensures high affinity of Urease for urea. High electron transfer characteristics and long shelf life (20 weeks) are the key features of the fabricated urea biosensor.

Mean temperature calculations in a turbulent channel flow for air and mercury

Direct numerical simulations (DNSs) in a turbulent channel flow are used to examine the behavior of the turbulent Prandtl number Prt for air (Pr = 0.71) and mercury (Pr = 0.025), with a view to calculating the mean temperature. Constant time-averaged (surface) heat flux (CHF) is used as a thermal boundary condition. For each Pr, four values of the Kármán number (h+ = 180, 395, 640, 1020) are used. Datasets for the constant heating source (CHS) are also examined. For Pr = 0.71, Prt is approximately 1.1 at the wall, varies between 0.9 and 1.1 in the region y+ <100, and is approximated by 0.9–0.3(y/h)2 for y/h > 0.2. The latter relation, with a low Re correction term (i.e. 25/h+), yields an excellent prediction for the mean temperature up to h+ = 2000, whereas a calculation based on Prt = 0.85 underestimates the mean temperature. The calculated maximum wall-normal turbulent heat flux and Nusselt number also agree well with the empirical relations over a wide range of h+. For Pr = 0.025, Prt departs significantly from unity inside the inner region (y/h < 0.2) owing to the strong conductive effect, whilst the magnitude in the outer region (y/h > 0.2) tends to approach that corresponding to Pr = 0.71 as h+ increases due to the increase in the Peclet number. The h+ dependence of Prt in the logarithmic and outer regions is represented adequately by the turbulent Peclet number, i.e. Pet=Prνt/ν. The resulting Prt relation, which is an extension of the expression established by Kays (1994), leads to a correct calculation of the mean temperature not only for mercury (Pr = 0.025) but also for liquid sodium (Pr = 0.01). The mean temperature defect profile exhibits an outer-layer similarity when Pe(≡RebPr) ≥ 2000; the Nusselt number is represented by Nu=4.8+0.0147Pe0.84 reasonably well.

In Situ Modification and Analysis of the Composition and Crystal Structure of a Silicon Target by Ion-Beam Methods

The method of Rutherford backscattering (RBS) with channeling is widely used in compositional analysis and structural determination. An experimental process line for in situ ion implantation and RBS spectrometry is presented, and its technical parameters are given. The parameters of a probing beam needed to reach a several-percent error in the study of distribution profiles of impurities and defects are detailed. The resolution of this method was estimated using the spectrum of alpha particles produced in the decay of 239Pu and based on the RBS spectrum from a silicon monocrystal. The implantation of Xe+ ions with an energy of 100 keV into a silicon monocrystal and the RBS analysis of targets in the channeling mode were performed without breach of vacuum conditions. The distribution profiles of implanted atoms and defects in irradiated monocrystals were examined.

Inspection of RC half-joint bridges in England: analysis of current practice

The strategic road network (SRN) in England carries 33% of traffic in England and Highways England's bridge management systems plays a crucial role in the maintenance of infrastructure assets along the SRN. Reinforced concrete half-joint structures are susceptible to deterioration and hard to inspect, hence they require special attention. Inspection data relating to half-joint structures on the SRN was gathered. Within this portfolio, 252 structures with half-joint-related defects were interrogated to classify the most common defects and identify any potential shortcomings in current inspection practice. Clear correlations were shown to exist between defect classes, emphasising the need for quality control and proper workmanship. A revised inspection methodology for half-joint structures that provides more comprehensive information about crack details, and a greater alignment between defect information and indicators of structural measures, is proposed. Concurrently, knowledge of the zonal crack location, crack orientation and crack severity helps inform decision making about the structural condition. There is scope for use of the methodology in conjunction with automated processing procedures to identify half-joint structures with particular defect characteristics and profiles. In this way, asset managers will be better able to allocate resources to structures with an increased risk of failure.

Quantitative detection of lamination defect in thin-walled metallic pipe by using circumferential Lamb waves based on wavenumber analysis method

Lamination defect is one of the common defects in the manufacturing process of seamless pipes. In this paper, the quantitative detection of a lamination defect in thin-walled metallic pipe using circumferential Lamb waves is studied. To interpret the received time-domain signals and extract useful information about the lamination defect, wavenumber analysis is performed on these signals. A three-dimensional finite-element model is established using Matlab and ABAQUS commercial software. Owing to the processing technique, an aluminum ring structure with a three-quarters circumference is considered to represent the metallic pipe. The lamination defect constructed in the model is a “zero-volume” crack, which stretches from θ = 180° to 270° and locates in the mid-plane of the wall. A five-cycle 0.41-MHz sinusoidal tone-burst signal modulated by a Hanning window is carefully chosen to generate the appropriate excitation wave, in CL0 mode. According to the received signals, the conclusion that the incident CL0 mode interacts with the lamination defect for numbers of times can be obtained. The space-amplitude curve of incident waves is also depicted to reveal the amplitude distribution of incident waves. A fully non-contact experimental platform that adopts an electromagnetic acoustic transducer as a transmitter and a laser ultrasonic inspection system as a receiver is set up to verify the finite-element model. Three different wavenumber analysis methods are performed on the wavefield signals to explain the detectability of the lamination defect separately through both numerical and experimental studies. It can be concluded that, from the variation of wavenumber, the continuity of structure can be deduced. Not only can the location be calculated with an error of less than 10%, but the profile of the lamination defect can also be imaged. It is also found that very good consistency exists between numerical and experimental results.

Distribution profiles of radiation donor defects in arsenic-implanted HgCdTe films

Mobility spectrum analysis and step-by-step chemical etching-based depth profiling have been employed for establishing distribution profiles of radiation-induced donor defects in an arsenic-implanted HgCdTe film grown by molecular beam epitaxy. Three electron species associated with specific defect layers in implanted material were detected, and defects responsible for these species were identified. The advantage of mobility spectrum analysis methodology over the use of traditional differential Hall effect-measurements with a single value of magnetic field was demonstrated for the ion-implanted HgCdTe.

Defect Manipulation To Control ZnO Micro-/Nanowire-Metal Contacts.

Surface states that induce depletion regions are commonly believed to control the transport of charged carriers through semiconductor nanowires. However, direct, localized optical, and electrical measurements of ZnO nanowires show that native point defects inside the nanowire bulk and created at metal-semiconductor interfaces are electrically active and play a dominant role electronically, altering the semiconductor doping, the carrier density along the wire length, and the injection of charge into the wire. We used depth-resolved cathodoluminescence spectroscopy to measure the densities of multiple point defects inside ZnO nanowires, substitutional Cu on Zn sites, zinc vacancy, and oxygen vacancy defects, showing that their densities varied strongly both radially and lengthwise for tapered wires. These defect profiles and their variation with wire diameter produce trap-assisted tunneling and acceptor trapping of free carriers, the balance of which determines the low contact resistivity (2.6 × 10-3 Ω·cm-2) ohmic, Schottky (Φ ≥ 0.35 eV) or blocking nature of Pt contacts to a single nano/microwire. We show how these defects can now be manipulated by ion beam methods and nanowire design, opening new avenues to control nanowire charge injection and transport.