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Surface resistance, Microwave measurements, Microwave devices, Alloys, and Measurement errors

Additive manufactured (AM) metals are a subject of much interest for their performance in passive microwave applications. However, limitations could arise due to artifacts, such as surface texture and/or roughness resulting from the manufacturing process. We have, therefore, adopted a parallel plate microwave resonator for the accurate measurement of the surface resistance of flat metal plates, allowing for microwave current flow in two orthogonal directions by simply exciting a different resonant mode (at 5.3 and 6.4 GHz), without the need to remove and refix the sample. The systematic and random errors associated with the measurement of surface resistance are very small, less than 1% and 0.1%, respectively. The technique is demonstrated with measurements on a range of samples of the alloys, AlSi10Mg and Ti6Al4V, manufactured by laser powder bed fusion, in addition to traditionally machined samples of bulk metal alloys of aluminum and brass. For AM samples of AlSi10Mg, we have studied the effect on the surface resistance of directional roughness features, generated by the laser raster paths, in directions transverse or parallel to microwave current flow. Importantly for passive microwave device applications, we demonstrate that these samples exhibit no systematic anisotropy of surface resistance associated with such surface features. [ABSTRACT FROM AUTHOR]

Ricci flow, Computational electromagnetics, Almond, Integral equations, Jet fighter planes, Quadrilaterals, and Surface preparation

We propose a surface meshing approach for computational electromagnetics (CEM) based on discrete surface Ricci flow (DSRF) with iterative adaptive refinement (AR) in the parametric domain for the automated generation of high-quality surface meshes of arbitrary element type, order, and count. Surfaces are conformally mapped by DSRF to a canonical parametric domain, allowing a canonical seed mesh to be mapped back to an approximation of the original surface. The new DSRF-based meshing technique provides a framework for generation of meshes with high element quality, aimed to greatly enhance the accuracy, conditioning properties, stability, robustness, and efficiency of surface integral equation CEM solutions. We demonstrate the ability of the proposed DSRF technique to produce meshes with near-optimal element corner angles for complicated, highly varied surfaces such as the NASA almond and a fighter jet model, using triangular, quadrilateral, and discontinuous quadrilateral elements. Other element types are also discussed. Where high-fidelity meshing is desired, the technique can capture fine-scale detail using very few high-order elements. Where low-fidelity meshing is desired, DSRF with AR can accurately recreate course-scale detail using standard first-order elements (e.g., flat triangular patches). [ABSTRACT FROM AUTHOR]

Electronic packaging, Microwave plasmas, Dielectric materials, Chemical processes, Electroless deposition, Microwave materials, Ohmic contacts, and Thermal stresses

Radio frequency (RF) or microwave printed circuit board (PCB) is a type of PCB designed to operate on signals in megahertz-to-gigahertz frequency (medium to extremely high frequency) ranges. The materials used to construct these PCBs are advanced composites with very specific characteristics for dielectric constant, loss tangent, and coefficient of thermal expansion (CTE). These microwave materials with critical values of very low dielectric loss and absolute dielectric constant allow high-speed signals to travel through the PCB with more stable impedance characteristics than in standard FR-4 dielectric materials. These microwave substrates are composite dielectric materials produced generally with combination of polytetrafluoroethylene (PTFE), ceramics, hydrocarbons, and/or various forms of glass. PTFE-based microwave PCB laminates, which require vias after drilling, are subjected to an appropriate surface modification for metallization, because of its hydrophobic nature and very low surface energy. Sodium-based wet chemical process followed by various copper deposition process techniques are commonly employed for metallization of microwave PCBs. In our study, plasma treatment process is used to generate microroughened surface in drilled vias, and electroless copper deposition followed by copper electroplating process have been employed for void-free metallization in microwave PCBs with enhanced plated-through-hole (PTH) reliability for space electronics packaging applications, as evidenced from the results of thermal stress and PTH bond strength tests conducted as per IPC-TM-650. [ABSTRACT FROM AUTHOR]

Vertical integration, Mass production, Copper oxide, Copper oxidation, Copper analysis, Copper surfaces, Analytical chemistry, and Nitrides

As 3-D packaging is expected to meet new requirements for next-generation system-in-packaging (SiP), various technologies have been discussed for vertical integration. To enable high-performance vertical interconnects, Cu-to-Cu bonding is an essential process for decreasing the metal-interconnect size between vertically stacked devices and for improving system performance. However, the high-temperature and high-pressure conditions of the Cu bonding process and copper surface oxidation are important issues to be resolved for better mass production, especially for chip-to-wafer bonding. In this study, a comprehensive analysis was performed on the effects of a two-step Ar and N2 plasma treatment used to create a copper nitride passivated surface. Chemical and structural analyses of the copper nitride surface showed that this two-step plasma treatment removed nonuniformly formed native copper oxides and formed an ultrathin copper nitride passivation layer. Electrical and mechanical analyses showed that the resulting uniform conductive copper nitride surface and plastic property have the potential to improve the quality of thermocompression bonding. The results of these comprehensive analyses demonstrate the excellent ability of copper nitride to passivate copper surfaces and indicate the possibility of achieving effective Cu bonding in air. [ABSTRACT FROM AUTHOR]

Wireless power transmission, Electromagnetic waves, Feedforward neural networks, and Intelligent networks

Intelligent surfaces exert deterministic control over the wireless propagation phenomenon, enabling novel capabilities in performance, security and wireless power transfer. Such surfaces come in the form of rectangular tiles that cascade to cover large surfaces such as walls, ceilings or building facades. Each tile is addressable and can receive software commands from a controller, manipulating an impinging electromagnetic wave upon it by customizing its reflection direction, focus, polarization and phase. A new problem arises concerning the orchestration of a set of tiles towards serving end-to-end communication objectives. Towards that end, we propose a novel intelligent surface networking algorithm based on interpretable neural networks. Tiles are mapped to neural network nodes and any tile line-of-sight connectivity is expressed as a neural network link. Tile wave manipulation functionalities are captured via geometric reflection with virtually rotatable tile surface norm, thus being able to tunable distribute power impinging upon a tile over the corresponding neural network links, with the corresponding power parts acting as the link weights. A feedforward/backpropagate process optimizes these weights to match ideal propagation outcomes (normalized network power outputs) to wireless user emissions (normalized network power inputs). An interpretation process translates these weights to the corresponding tile wave manipulation functionalities. [ABSTRACT FROM AUTHOR]

Packaging, Electric insulators & insulation, Flip chip technology, Semiconductors, Vacuum chambers, Numerical calculations, and Electric fields

Delamination between the molding compound and the die surface is a common failure pattern in the semiconductor package industry. Plasma treatment is a standard process to clean and activate the die surface to enhance the bonding force between the molding compound and the die surface in the packing procedure. However, the unexpected delamination still happens and results in a huge commercial loss for the packaged products. This study adopts experimental and numerical approaches to systematically investigate the delamination risk for plasma treatment before compound molding. A vacuum chamber is established to visualize the plasma distribution and the oxidation condition of the lead frames placed on the metal and the insulator rails. Moreover, a numerical calculation is used to systematically predict the plasma distribution over the lead frame and die surface. Results show that the lead frame placed on the metal rail exhibited a higher electric field gradient than that placed on the insulation rail. Moreover, the copper lead frame placed on the insulation rail exhibits a lower electric field gradient and less metal oxidation on the die surface. The delamination risk for semiconductor packaging can be systematically predicted and efficiently reduced before the packing process with the results obtained in the present study. [ABSTRACT FROM AUTHOR]

Semiconductor manufacturing, Manufacturing processes, Convolutional neural networks, Semiconductor wafers, Surface defects, and Robotic welding

Semiconductor wafer is widely used in welding robot, spray robot, unmanned material delivery vehicle, and detection station sensor. The defects of semiconductor wafer, such as stains, burrs, scratches, and holes generated in the manufacturing process, severely affect the quality of downstream products. Therefore, the inspection of wafer defect could not be neglected. Traditional semiconductor wafer defect inspection methods based on handcrafted features heavily rely on the expertise and are limited in some application scenario. In this article, a novel method based on deep convolutional neural networks for semiconductor wafer surface defect inspection is proposed. First, a new structure of feature pyramid networks with atrous convolution (FPNAC) is developed to extract the features and to generate feature maps. Second, the feature maps are fed into region proposal network (RPN) to generate region proposals. Finally, the region proposals are aligned to corresponding size as the inputs of deep multibranches neural network (DMBNN) consisting of three branches, to classify and segment the defects precisely. Experimental results demonstrate that the proposed method yields good comprehensive performance with mean pixel accuracy (MPA) 93.97% and mean intersection over union (MIoU) 83.58%. [ABSTRACT FROM AUTHOR]

Convolutional neural networks, Metallic surfaces, Metal defects, Inspection & review, and Pyramids

Visual surface defect inspection for metal part has become a rapidly developing research field within the last decade. But due to the variances of defect shapes and scales, the inspection of tiny and irregular shape defects has posed challenges on the robustness of the inspection model. In this context, a deep learning method based on the deformable convolution and concatenate feature pyramid (CFP) neural networks is proposed to improve the inspection. We design a deformable convolution layer in the neural networks as an attention mechanism to adaptively extract the features of defect shape and location, which enhances the inspection of the defects with large shape variances. We also merge the multiple hierarchical features collected from different deformable convolution layers by the CFP, which improves the inspection of tiny defects. The results show that the proposed method has a better generalization ability than traditional convolution neural networks. [ABSTRACT FROM AUTHOR]

Schottky barrier diodes, Wide gap semiconductors, and Aluminum gallium nitride

Critical design parameters for AlGaN/GaN Schottky barrier diodes (SBDs) are analyzed in this work using TCAD computations and detailed experiments. A comprehensive TCAD-based computational modeling approach is developed for GaN-based SBD. Breakdown mechanisms in SBD for unintentionally doped (UID) buffer, Fe-doped buffer and C-doped buffer are studied. For the first time, we have reported impact of anode recess, on breakdown and leakage behavior of SBD, in correlation with interface defects. Using these insights an optimum recess design strategy has been presented and is validated experimentally. Furthermore, for the first time, we have revealed critical repercussions of the field plate termination on SBD’s breakdown, leakage as well as transient behavior. Forward and reverse recovery measurements were carried out to study the diode’s transient performance as a function of field plate design. Various performance matrices such as diode current collapse, reverse current overshoot and reverse recovery time were studied experimentally as a function of field plate design. Moreover, the field plate-dependent electro-thermal behavior of SBD was studied using TCAD computations and experiments. Using the systematic device design approach we have experimentally demonstrated large periphery SBD with 15 A forward current at 5.5 V. [ABSTRACT FROM AUTHOR]

Field-effect transistors, Chemical vapor deposition, Discontinuous precipitation, Charge carrier mobility, Surface roughness, and Dielectric films

In this article, an effective way of chemical modification on the dielectric surface (Al2O3) is investigated to chemical vapor deposition (CVD)-grown high-quality monolayer MoS2 and the relevant back-gated FETs are fabricated without MoS2 transfer. As a result, the size of the triangle MoS2 is increased and its quality is improved as the surface of Al2O3 is treated by H2SO4. Furthermore, as compared with the gate dielectrics of the SiO2 and as-deposited Al2O3, the fabricated transistor with the H2SO4-treated Al2O3 as gate dielectric achieves better electrical properties: high carrier mobility of 12.9 cm2/Vs (~10 times higher than the untreated sample, ~5.2 times higher than the SiO2 gate-dielectric sample), small subthreshold swing of 110 mV/dec, and high ON/OFF ratio of $3\times 10^{{6}}$. The involved mechanisms are attributed to the fact that the H2SO4-treated Al2O3 not only can increase its surface roughness to promote the nucleation and high-quality growth of MoS2 but also can improve the quality of the MoS2/Al2O3 interface. This simple chemical-modification treatment will open up an effective approach of combining the high-crystallinity CVD-MoS2 with the high- ${k}$ dielectric without MoS2 transfer required. [ABSTRACT FROM AUTHOR]

Mathematical models, Failure mode & effects analysis, Semiconductor devices, Surface preparation, and Rough surfaces

In this study, we have developed a method to quantify inherent conditioner-to-conditioner variation using a mathematical model. Quantification of the lifetime of pad and conditioner in a chemical mechanical planarization (CMP) process using the model is also elucidated. Three conditioner types are selected based on their aggressiveness, and conditioning experiments are performed with five different conditioners of the same type to quantify the variation. Assuming exponential decay equation for pad wear rate (PWR), a simple model is developed and the model parameters, K and ${\lambda }$ , are derived in numeric form. K, a measure of conditioner aggressiveness, can be used as a metric to assess conditioner-to-conditioner variation, while ${\lambda }$ is a measure of conditioner lifetime. K and ${\lambda }$ values are also used to predict the failure mode of a CMP process (conditioner or pad failure mode). Pad groove depth and PWR curves of five different conditioners of the same type as a function of time are plotted along with upper and lower limits. The limiting factor (low PWR due to conditioner decay or excess pad removal) is identified to predict the failure mode. An example for each failure mode (A122 and 8031C1 conditioners for conditioner and pad failure modes, respectively) is presented. [ABSTRACT FROM AUTHOR]

Induction heating, Zero current switching, Metals, Industrial metals, and Zero voltage switching

A new multiresonant three-phase utility frequency ac (UFAC) to high-frequency ac (HFAC) direct power converter for the industrial metal hardening induction heating (IH) applications is presented in this article. The proposed ac–ac converter features direct frequency conversion with the wide range of soft switching by means of the minimized numbers of bidirectional switches. The conducting current of bidirectional switches can be reduced effectively owing to the multiresonant tank while keeping a high power in the IH load. Accordingly, the practical power converter with simplicity, cost-effectiveness, and high efficiency can be realized on the basis of a simple pulse-frequency modulation (PFM). The circuit topology and operating principle of the proposed converter are described, after which the design procedure of the multiresonant tank and switching frequency is presented. The performances on the soft switching and the steady-state PFM characteristics of the ac–ac converter are evaluated in experiment with the 1.7 kW/85–90-kHz prototype. Finally, the feasibility of the proposed ac–ac converter is evaluated from a practical view point. [ABSTRACT FROM AUTHOR]

Adaptive control systems, Chattering control (Control systems), Sliding mode control, Permanent magnet motors, and Lyapunov functions

In order to enhance the speed control performance of the permanent magnet synchronous motor (PMSM) with internal and external disturbances, a new adaptive terminal sliding mode reaching law (ATSMRL) is proposed with continuous fast terminal sliding mode control (CFTSMC). Firstly, the ATSMRL is presented with the aim of reducing the input control efforts, which can dynamically adopt all positive aspects in terms of the finite time convergence, high tracking precision, and reduction of the chattering in the control input of the system. Secondly, an extended sliding mode disturbance observer (ESMDO) is designed to estimate the total disturbances of the system, and then the estimated disturbance has been brought for the feed-forward compensation technique, which would enhance the disturbance rejection ability of the system. Afterwards, the close loop stability is validated by the Lyapunov function. Finally the comprehensive numerical and experimental analyses have been carried out to demonstrate the superiority of the ATSMRL method than those of conventional exponential sliding mode reaching law (ESMRL) and terminal sliding mode reaching law (TSMRL). [ABSTRACT FROM AUTHOR]

Rough surfaces, Electromagnetic wave scattering, Discrete Fourier transforms, Power spectra, Power density, and Separation of variables

This article presents a new approach to analytically compute high-frequency (HF) electromagnetic (EM) scattering from an arbitrary undulating rough surface according to the statistical characteristics of its geometric fluctuation. The integral expression of the scattering coefficient is derived from Kirchhoff approximation (KA) and extended to arbitrary spectra. Two methods are presented to calculate the integral: 1) the discrete Fourier transforming method based on the autocorrelation function (ACF) (KAC) and 2) the convolution method based on the power spectrum density function (KAW). For some analytically expressed spectra, the scattering coefficients can be calculated directly by the KAW and KAC methods according to its power spectrum density (PSD). The analytical expressions of classical KA for Gaussian and exponential spectrum are used to validate the proposed methods. For the case of unknown undulation height spectra of rough surfaces, the ACF is statistically calculated first, and then the KAC and KAW methods are used to calculate the average scattering coefficients numerically. Moreover, the numerical results show that the KAW method takes up more memory to retain enough energy of the ACF for accurate scattering coefficients. The two new methods are effective in the range of $\theta _{i} $ from 0° to 45° and have broad application prospects for real scenarios. [ABSTRACT FROM AUTHOR]

Radio telescopes, Reflector antennas, Radio astronomy, and Surface preparation

The reflector surface of a large reflector antenna may even consist of thousands of panels, and if the panel molds with high-precision requirements are fabricated uniquely for each ring, the overall cost will be very high. Therefore, from a perspective of reducing the cost, the mold sharing design is of particular significance. In order to obtain the minimum number of molds satisfying the given electronic performance index, the electronic performance-oriented mold sharing design is suggested, in which the effective surface accuracy is used to evaluate electrical performance. The smaller the combined effective root-mean-square (rms) error value introduced after sharing the mold, the more preferential these rings should share the mold to reduce the number of molds. Based on such idea, a fast mold reduction process is presented, which can give the minimum number of molds quickly according to the electrical performance requirements. During this process, a combined effective rms value matrix and a mold sharing discriminant matrix are defined and used. To construct these two matrices, the panel normal error induced by mold sharing is derived, and the optimal mold position is determined first. As a test problem, application of the proposed method to mold reduction of a 110 m radio telescope is presented, and the discussions of the results are given. [ABSTRACT FROM AUTHOR]

Compression molding, Electrodes, Accelerated life testing, Laser ablation, and Silicon wafers

Objective: The purpose of this paper is to establish fabrication method of cyclic olefin copolymer(COC)-based neural electrode. Methods: The fabrication started with preparing COC pellets into COC films by compression molding. Metal layers were deposited on the COC film and attached to a silicon wafer. Laser ablation was used to cut the outer edges and mark alignment keys. The metal layers were patterned using standard photolithography procedures. Finally, the isolated electrodes were laminated. To ensure that the resulting electrode is safe and suitable for long-term implants, in vitro biocompatibility test, impedance evaluation, accelerated soak test, and repeated bend test were conducted. Results: Cytotoxicity test and elution test confirmed the biocompatibility in vitro. The basic performance was not hindered compared to other polymer-based electrodes, and the longevity of the electrode was validated by accelerated soak test. However, repeated bend test revealed that the material might not be suitable for applications where constant bending is required. Conclusion: The COC-based neural electrode was successfully fabricated. The material showed several merits such as biocompatibility, thermoplasticity, low water absorption rate, and high transparency, but should be limited to applications where repeated bending is not required. Significance: Electrical circuits in implantable prosthetic devices must be hermetically encapsulated for a long period of time. Material such as COC with extremely low water absorption rate could have a significant impact on the longevity of these devices. [ABSTRACT FROM AUTHOR]

Manufacturing processes, Light emitting diodes, Angles, Petri nets, and Elastic deformation

In order to improve the optical and electrical consistency in lighting and display, light emitting diode (LED) dies should be sorted and aligned precisely one by one. As per given current production process practices, the sorting efficiency is required to be more than 36 thousand units per hour (KUPH), while the alignment deviation should not exceed 1 mil (25.4 $\mu \text{m}$) and all dies’ angle deviations should fall within 5°. Among all the requirements, the chip angle correction is particularly difficult to achieve because a small die correction on wafer would cause a change in all dies’ positions, leading to significant performance degradation. This results in an ambiguity, due to the difficulty in balancing efficiency and accuracy. In this article, the influence factors of the accuracy deviation caused by the angle correction are analyzed in detail, and the negative effect caused by tiny deformation of the elastic substrate is studied with comprehensive experiments. The parallel scheduling mechanism of the angle correction is analyzed, and the influences on sorting performance are evaluated with stochastic petri net (SPN) model, so that the suitable working area is disclosed. A local compensation strategy using the local deformation trend of the membrane is utilized to optimize the accuracy of precorrection. Further, the alignment area is actively compensated according to the alignment precision requirements, so that the performance and accuracy requirements are balanced. In the chip packaging field, microchip angle correction is often needed. This method is applicable to similar situation and chips are adhesive on membrane. [ABSTRACT FROM AUTHOR]

Thin films, Intraocular lenses, Drug delivery systems, Atomic force microscopy, Spin coating, Scanning electron microscopy, and Transparency (Optics)

To design, develop and study a novel drug delivery system for intraocular applications. The spin coating technique was applied to develop a polymeric, drug-eluting thin film consisting of a blend of organic polymers [poly (D, L lactide coglycolide) lactide: glycolide 75: 25, PLGA and polycaprolactone, PCL] and dexamethasone on the surface of intraocular lenses (IOLs). The initial durability of the IOLs during spinning was assessed. Information about the structural and optical properties of the modified IOLs was extracted using atomic force microscopy, scanning electron microscopy and spectroscopic ellipsometry. A drug release study was conducted for 8 weeks. The IOLs were durable in spinning speeds higher than the ones used to develop thin films. Single-layer thin films were successfully developed on the optics and the haptics of the lenses. The films formed nanopores with encapsulated aggregates of dexamethasone. The spectroscopic ellipsometry showed an acceptable optical transparency of the lenses regardless of the deposition of the drug-eluting films on their surface. The drug release study demonstrated gradual dexamethasone release over the selected period. In conclusion, the novel drug-eluting IOL system exhibited desired properties regarding its transparency and drug release rate. Further research is necessary to assess their suitability as an intraocular drug delivery system. [ABSTRACT FROM AUTHOR]

Acoustic emission, Grinding wheels, Piezo-electric detectors, Acoustic imaging, Cutting tools, Piezoelectric transducers, and Acoustic transducers

The main difficulty in the grinding process is to identify the correct moment to dress the grinding wheel. Therefore, the cutting tool (grinding wheel) must be monitored. In this context, an innovative technique was developed in this article to obtain an image from the surface of the grinding wheel during the dressing process, based on acoustic images acquired through a piezoelectric diaphragm or piezoelectric buzzer. To this end, scratches (faults) are made on a grinding wheel, after which tests are performed at various dressing depths, and signals are collected by an acoustic emission (AE) sensor and a piezoelectric diaphragm. Based on these signals, frequency bands are evaluated to obtain acoustic images that would accurately and clearly represent the scratches imprinted on the grinding wheel. Finally, the performance of the two sensors (AE sensor and piezoelectric diaphragm) are compared, and the results are analyzed in light of the dressing conditions under study. The results indicate that the piezoelectric diaphragm is as efficient in obtaining acoustic maps of the grinding wheel surface as the AE sensor and in some machining conditions, it provides superior results to those obtained when monitoring the tool with the AE sensor. [ABSTRACT FROM AUTHOR]

Polypropylene films, Electric charge, Triboelectricity, Electric potential measurement, Corona discharge, and Electric potential

In roll-to-roll manufacturing of products, such as thin films, fibers, textiles, or membranes, the generation and accumulation of electric charges by the triboelectric effect represents a major source of electrostatic hazards. The best solution to this problem is to eliminate these charges. The aim of this article is to pave the way to the use of a triode-type corona electrode system at an industrial frequency (50 Hz) for active neutralization of electrically charged insulating films. The experimental study was carried out on dc corona charged polypropylene films that were neutralized by a sinusoidal corona discharge. The neutralization efficiency was evaluated by noncontact measurement of the electric potential at the surface of charged and neutralized polypropylene film samples. The response surface methodology was used for quantifying the effects of the various influential factors (i.e., voltage amplitude, duration of exposure to the discharge, and relative position of the neutralizer with respect to the sample) and optimizing the neutralization process. [ABSTRACT FROM AUTHOR]