Gaussian Defects Research Articles

Ultrasonic Rough Crack Characterization Using Time-of-Flight Diffraction With Self-Attention Neural Network.

Time-of-flight diffraction (ToFD) is a widely used ultrasonic nondestructive evaluation (NDE) method for locating and characterizing rough defects, with high accuracy in sizing smooth cracks. However, naturally grown defects often have irregular surfaces, complicating the received tip diffraction waves and affecting the accuracy of defect characterization. This article proposes a self-attention (SA) deep learning method to interpret the ToFD A-scan signals for sizing rough defects. A high-fidelity finite-element (FE) simulation software Pogo is used to generate the synthetic datasets for training and testing the deep learning model. Besides, the transfer learning (TL) method is used to fine-tune the deep learning model trained by the Gaussian rough defects to boost the performance of characterizing realistic thermal fatigue rough defects. An ultrasonic experiment using 2-D rough crack samples made by additive manufacturing is conducted to validate the performance of the developed deep learning model. To demonstrate the accuracy of the proposed method, the crack characterization results are compared with those obtained using the conventional Hilbert peak-to-peak sizing method. The results indicate that the deep learning method achieves significantly reduced uncertainty and error in rough defect characterization, in comparison with traditional sizing approaches used in ToFD measurements.

Comparing the Buckling Strength of Spherical Shells With Dimpled Versus Bumpy Defects

AbstractWe investigate the effect of defect geometry in dictating the sensitivity of the critical buckling conditions of spherical shells under external pressure loading. Specifically, we perform a comparative study between shells containing dimpled (inward) versus bumpy (outward) Gaussian defects. The former has become the standard shape in many recent shell-buckling studies, whereas the latter has remained mostly unexplored. We employ finite-element simulations, which were validated previously against experiments, to compute the knockdown factors for the two cases while systematically exploring the parameter space of the defect geometry. For the same magnitudes of the amplitude and angular width of the defect, we find that shells containing bumpy defects consistently exhibit significantly higher knockdown factors than shells with the more classic dimpled defects. Furthermore, the relationship of the knockdown as a function of the amplitude and the width of the defect is qualitatively different between the two cases, which also exhibit distinct post-buckling behavior. A speculative interpretation of the results is provided based on the qualitative differences in the mean-curvature profiles of the two cases.

Reliability analysis of cost-efficient CH3NH3PbI3 based dopingless tunnel FET

Electrostatically-doped TFETs (ED-TFETs) are amongst the most widely used cost-efficient steeper devices due to the use of charge-plasma technique and tunneling mechanism. However, the reliability analysis of ED-TFETs is considered an important concern for the research community. Most studies have only focused on improving the performance of ED-TFETs such as dopingless (DL)-TFET in terms of on-current (I ON), subthreshold swing (SS) and threshold voltage (V th), rather than investigating the reliability issues. In this context, the aim of our work is to investigate the reliability analysis of our previously reported methyl-ammonium lead tri-iodide materials based DL-TFET (MAPbI3-DL-TFET). The influence of interface trap charges, shallow and deep defects on the electrical and analog performance of MAPbI3-DL-TFET has been analyzed using the Silvaco ATLAS tool at room temperature. Extensive results produced show that deep-level (Gaussian) defects impact the performance of the device prominently while the tail defects affect the device performance insignificantly. The present findings showed that the donor/acceptor trap charges impact the device in the subthreshold region considerably, while in the superthreshold region the impact of trap charges is marginal. In our view, these results emphasize the reliability analysis of MAPbI3-DL-TFET for the very first time. We hope that our research will be useful and valuable for DL-TFET manufacturers.

Spontaneous Formations of Dynamical Steady States in Polariton Condensates

We present a numerical analysis on dynamical steady states of polariton Bose–Einstein condensates (BECs) in an incoherent exciton reservoir driven by a ring-shaped optical pump. The balance between the loss and gain of polariton BEC induces a variety of steady states with different configurations, including approximate Gaussian distribution and topological defects, such as vortex–antivortex pairs, vortices with a winding number, and solitons. Besides, the system becomes unstable under fast decay rates and small pumping ring, where BECs can no longer exist in the long-time limit. We also confirm the soliton is dynamically stable in this system, with a steady polariton current induced by the repulsive polariton–polariton and polariton–exciton interactions.

Soft Recovery Process of Mechanically Degraded Flexible a-IGZO TFTs With Various Rolling Stresses and Defect Simulation Using TCAD Simulation

We examine the effects of repetitive rolling stress on thin-film transistors (TFTs) using various rolling radii, and evaluate the subsequent thermal treatment at various temperatures. After applying repetitive rolling stress, the electrical characteristics of the TFTs changes. In particular, change of subthreshold swing (SS) is significant than that of threshold voltage (Vth), and saturation mobility ( $\mu _{\text {sat}}$ ). We simulated the electrical performance of TFTs using technology computer-aided design (TCAD) to quantitatively ascertain the change to donor-like and acceptor-like defects in the active region. Both Gaussian donor-like defects (NGD) and acceptor-like defects (NGA) increased under mechanical strain due to the formation of oxygen-related defects, oxygen vacancy (Vo), and oxygen interstitials (Oi). In addition, negative bias illumination stress (NBIS) reliability results show that degraded TFTs at higher rolling stress yield more variation of threshold voltage ( $\Delta \text{V}_{\text {th}}$ ) and $\Delta $ SS due to increase in interface trap site, and defect sites. The rolling stress generates more oxygen-related defects, Vo and Oi, which act as TFT degradation factors. Finally, we investigate the possible recovery mechanism of mechanically degraded TFTs through thermal treatment. Thermal treatment at 150 °C and 250 °C cannot recover the electrical performance of mechanically stressed TFTs and NBIS reliability to before rolling state. Therefore, we used TCAD simulation to speculate the origin of incomplete recovery. We thought that this incomplete recovery originated from oxygen dimers (O-O) formed from Oi under mechanical stress.

Numerical analysis of Mg2Si/Si heterojunction DG-TFET for low power/high performance applications: Impact of non- idealities

Abstract In the advanced technology nodes, conventional MOSFETs are being replaced by tunnel field effect transistors (TFETs), due to its potential of achieving subthreshold swing (SS) less than 60 mV/decade. However, certain constraints are to be met to improve the performance of TFET in terms of higher ON current (ION) and lower threshold voltage (Vth). Here, in this paper, magnesium silicide/silicon (Mg2Si/Si) heterojunction double gate TFET (Mg2Si/Si HDG-TFET) is explored and is simultaneously compared with conventional silicon double gate TFET (Si DG-TFET). Results depict superior performance of Mg2Si/Si HDG-TFET as compared to conventional Si DG-TFET, in terms of dc characteristics, i.e., ION, Vth, SS, and ION/IOFF ratio. Obtained Vth (0.26 V), SS (10.05mV/decade) and ION/IOFF ratio (1013) for the case of Mg2Si HDG-TFET shows an improvement of 77%, 49% and 10 decades respectively compared to counterpart i.e., Si DG-TFET. In particular, this improvement in the performance of Mg2Si/Si HDG-TFET over Si DG-TFET is attributed to staggered type-II heterojunction interface at the source-channel junction, which leads to reduction of the width for interband tunneling barrier and hence, improves ION. This viability of the device is also determined by analyzing the impact of non-idealities present in the device. In this respect, the Gaussian and tail defects are considered in the bulk of Mg2Si. The results reveal that the Gaussian defects alter the device characteristics mainly in the subthreshold regime, whereas, in the ON state, the impact of defects is minimal. Further, it is obtained that the device is much immune for tail defects in comparison with the Gaussian defects. The CV analysis reveals a marginal degradation in parasitic capacitances for Mg2Si/Si HDG-TFET as compared to Si DG-TFET. However, this degradation can be overlooked against the remarkably enhanced drain current. Thus, the device overcomes the bottleneck of TFET and provides high ION and low Vth without degrading the other performance parameters and hence is suitable for low power analog and digital applications.

Contact angle hysteresis in a microchannel: Statics

We study contact angle hysteresis in a chemically heterogeneous microchannel by tracking static meniscus configurations in the microchannel upon varying the volume of liquid. We first construct a graphical force balance similar to a previous approach by Joanny and de Gennes for this system, though here with a straight contact line. It is shown that hysteresis is induced by wettability gradients above a finite threshold value. This is also visualized in a phase-plane plot enabling to easily predict stick-slip events of the contact line and the occurrence of hysteresis. Above the threshold and for nonoverlapping Gaussian defects, we find good agreement with the expressions by Joanny and de Gennes for the hysteresis amplitude induced by a dilute system of defects. In particular, the hysteresis amplitude is found to be proportional to the square of the defect force and to the defect concentration. For a model sinusoidal heterogeneity, decreasing the ratio between the heterogeneity wavelength and the microchannel gap size brings the system from a subthreshold regime, to a stick-slip dominated regime, and finally to a regime with a quasiconstant advancing and receding angle. In the latter case, the hysteresis amplitude is found to be proportional to the defect force. We also consider an unusual heterogeneity for which the gradients of increasing and decreasing wettability are different. In such a situation breaking the left/right symmetry, whether or not hysteresis is observed will depend on the side the liquid enters the microchannel.

Correlation between Threshold Voltage and the S-factor of Polysilicon Thin-Film Transistors and the Changes due to Bias Stress

The correlation between threshold voltage (VTH) and the inverse of the subthreshold slope (S-factor) of polysilicon thin-film transistors (TFTs) has been investigated. The S-factor of poly-Si TFTs increases linearly in proportion to VTH. A linear relationship is also seen between the changes of the S-factor and VTH owing to bias stress. These are consistent with the results of numerical simulation with a homogeneous density of states having exponential band tails and Gaussian defects.

Practical approach for modeling extreme ultraviolet lithography mask defects

An approximate method is proposed to calculate the extreme ultraviolet (EUV) scattering from a defect within a multilayer coating. In this single surface approximation (SSA) the defective multilayer structure is replaced by a single reflecting surface with the shape of the top surface of the multilayer. The range of validity of this approximation has been investigated for Gaussian line defects using two-dimensional finite-difference-time-domain simulations. The SSA is found to be valid for sufficiently low aspect ratio defects such as those expected for the critical defects nucleated by particles on the mask substrate. The critical EUVL defect size is calculated by combining the SSA with a multilayer growth model and aerial image simulations. Another approximate method for calculating the aerial image of an unresolved defect is also discussed. Although the critical substrate defects may be larger than the resolution of higher numerical aperture cameras, the point defect approximation provides a useful framework for understanding the printability of a wide range of defects.

Effects of multilayer mask roughness on extreme ultraviolet lithography

Effects of multilayer roughness are explored based on rigorous electromagnetic simulation with TEMPEST and aerial image calculation with SPLAT. The TEMPEST simulation on small roughness features using an average material properties technique is validated by comparison with the simulation using finer gridding and approximate analytical methods. Simulations for rms roughness from 0 to 1.4 nm show a reflectivity reduction, a phase shift, and a polarization dependence. Midsize Gaussian defects are shown to be slightly less printable in the presence of roughness. For extreme ultraviolet lithography systems with roughness rms of 0.15 nm, the above effects are very second order.

A method for obtaining an approximate Wiener filter

The Wiener restoration filter yields the minimum mean-square error between the restored image and the true object function. However, it has found limited use because, in its usual formulation, it requires information about the object power spectrum which is generally unknown. In this paper, it is shown that the Wiener filter can be derived from the noise-free image power spectrum, and a method is presented for estimating this from the observed data. From this estimate an approximate Wiener filter was calculated. The method was tested on three sets of simulated data which included a constant background, rectangular defects, and Gaussian defects at varying contrast and noise levels. The performance of the approximate Wiener filter was compared both to the true Wiener filter and to the standard 1-2-1 three-point smooth. The results confirmed that the approximate Wiener filter adapted to the information content of the observed data and closely matched the performance of the true Wiener filter. The approximate Wiener filter outperformed the three-point smooth in all cases, especially at low contrast and high noise levels. The approximate Wiener filter can be calculated without operator intervention and requires little additional computation time over conventional Wiener filter techniques.