Thickness Nonuniformity Research Articles

Partial abrasion modeling and variable load characteristics analysis for high-speed load sensing electro-hydrostatic actuator pump of aircraft

The load-sensing electro-hydrostatic actuator (LS-EHA) allows to reduce the thermal output and enhance the dynamic characteristics of the more electric aircraft (MEA). In addition, the forecasting of the LS-EHA is crucial for its efficient functioning. This study proposes a novel model for the analysis of overturning and wear characterization of the slipper, while focusing on the partial abrasion. The transient thermoelastic hydrodynamic (TEHD) lubricating analysis of the slipper pair is solved by an analytical model along with the finite difference method. In the proposed partial abrasion model, the non-uniformity of the oil film thickness and the partial abrasion contour for the slipper bottom surface are considered through the discrete friction area approach in order to reach a higher precision. Afterward, the overturning behavior characteristics of the slipper and the variation law in its overturning behavior under different rotation speeds, load delivery pressures, and swashplate angles are analyzed. The obtained results demonstrate that the lubricating oil film field is unevenly distributed, and the overturning behavior of the slipper has certain variable load characteristics. Finally, the effectiveness and precision of the proposed partial abrasion model are validated through comparative simulation experiments and analysis.

Achieving low-porosity AlSi10Mg cladding layers for the additive repair of aluminum alloy parts by directed energy deposition

Directed Energy Deposition (DED) has broad application prospects for repairing damaged aluminum alloy parts such as piston aero-engine casing. However, due to the low laser absorptivity and the complex thermal cycle process, it is challenging to obtain aluminum alloy cladding layers with high-quality morphology and low-porosity by DED method. In this work, a series of individual stages of DED process are studied during single-tracks overlapping and layers stacking. Correspondingly, the within layer scanning strategy, inter-layer stacking strategy, and process parameters are examined carefully. Using the proposed DED processing flow that combines substrate preheating with intermittent process, the deposited layers without balling and collapse are successfully achieved. Furtherly, the bi-directional scanning strategy for single-tracks overlapping within layer is proposed to compensate the thickness nonuniformity caused by heat accumulation. The inter defects identified as “lack of fusion” and “gas pores” are observed in the cladding layers with uniform surface. By analyzing the pore formation mechanism and considering the energy distribution and re-melting, the multi-layer offset stacking strategy is proposed to inhibit the porosity to 0.25 %. Combined with the optimized process parameters, the porosity is reduced up to 0.09 %, ensuring the density of the DED deposition coating. This work provides new pathway and direct guidance for fabricating high-quality AlSi10Mg cladding layers during the DED repairing of valuable aluminum alloy parts.

Improvement of titanium film uniformity by magnetron sputtering with electromagnetic coil design

A novel magnetron assembly based on a combination of permanent magnet and adjustable electromagnetic coil is proposed for improved uniformity of the magnetron sputtering deposition process. The design of the magnetron sputtering system containing a rotating substrate and an off-axis arranged magnetron. A numerical framework has been developed to describe the evolution of the plasma density and distribution of sputtered particles. Specifically, the finite element method (FEM) was used to calculate the magnetic field and to model the magnetron sputtering discharge, and binary-collision Monte Carlo method was used to determine the transport of sputtered atoms to the substrate. Through parametric analyses, it was found that increasing the substrate-to-target distance, gas pressure, and coil current intensity benefits the uniform distribution of particles. The condition where the off-axis displacement of the magnetron effectively enhances uniformity. A strategy for optimizing deposition uniformity by combining adjustable current with an off-axis magnetron arrangement was proposed, which reduce the non-uniformity of film thickness by 77.6 % compared to the traditional fixed magnetic field model.

Influence of dimensional deviation and thickness non-uniformity on the small-size specimen tensile results of CLF-1 steel

Tensile testing of small-size specimens has been widely used to evaluate the influence of neutron irradiation on the mechanical properties for structural materials of fusion reactors. In recent years, researchers have been trying to standardize small-size specimen tensile test method. In the present paper, we have investigated the influence of dimensional deviation and thickness non-uniformity on the tensile results of small-size specimen by both experiments and finite element simulations, based on one of the candidate structural materials of fusion reactor, i.e. CLF-1 steel. It was found that under the conditions of small grain size, small metallurgical defect size and suitable specimen preparation, the tensile results of SS-J3 specimen could be close to the results of large-size specimen. Slightly higher yield and ultimate strengths for small specimens may be caused by the surface treatment of the wheel grinding. The repeatability of ultimate strength was better than that of yield strength, and the repeatability of elongation was worse than that of strength. For tensile tests on eight SS-J3 specimens, the maximum difference in total elongation was about 3 %. With ±0.1 mm deviation of thickness and parallel width, the maximum variation in total elongation was about 1.8 %. The ductility properties were sensitive to specimen's thickness non-uniformity, the measured uniform and total elongations would obviously decrease even with 0.01 mm thickness non-uniformity.

Fabrication of organic thin films using slit nozzle with a wide viscosity spectrum

A slit nozzle with a broad viscosity spectrum is highly demanded for slit coating of various materials with different viscosities without a compromise on the film quality. To this end, we have fabricated a multi-cavity slit nozzle with the inlet and vent holes for each cavity. Compared with a slit nozzle with a high-volume single cavity, such a multi-cavity slit nozzle further reduces the dead volume and thus material waste. As a design parameter in computational fluid dynamics (CFD) simulations for the multi-cavity slit nozzles, we have calculated the coefficient of variation in the internal pressure (Pcv) of the cavity and investigated the correlation between the simulated Pcv value and the measured thickness uniformity of low-viscosity (tens of cPs) poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS), medium-viscosity (5000 cPs) polydimethylsiloxane (PDMS), and high-viscosity (18,000 cPs) hard-PDMS films. It is addressed that the Pcv value that can ensure the thickness non-uniformity of less than 5 % is of the order of 1 %, and the internal pressure of the nozzle should not exceed a specific upper limit to protect a coating system against overload. Based on the design guideline provided, we have found that the upper limit of the viscosity spectrum of the triple-cavity slit nozzle with the 800-μm-thick shim is 79,000 cPs when the flow rate is 50 ml/min. Using the multi-cavity slit nozzle, we have fabricated a highly uniform PDMS film exhibiting the tensile strain as high as 180 %, which can be used as a substrate for stretchable displays. Furthermore, we have successfully fabricated flexible OLED stripes on the slit-coated conductive PEDOT:PSS stripes, showing the average luminance of 72.8 cd/m2 at 5 V and inter-stripe luminance non-uniformity as low as 8.2 %.

Deposition and structural investigation of uniform AlN(100) films at wafer scale through RF magnetron sputtering

a-axis-oriented AlN(100) films are identified as promising candidates for surface acoustic wave devices owing to their high transversal-acoustic velocity. Achieving uniform films across a wafer scale is crucial for enhancing device performance and minimizing manufacturing costs. In this study, we employ radio-frequency magnetron sputtering to deposit AlN(100) films on 2-in Si(100) wafers. We further examine the influence of various process parameters on the nonuniformity of film thickness and structural properties, including crystallite size, microstrain, and dislocation density. The optimization of parameters leads to the selection of a gas flow ratio of N2:Ar = 4:7, a sputtering power of 160 W, and a substrate temperature of 350 °C. Under these optimized conditions, the AlN films not only demonstrate a preferred (100) orientation and remarkable crystallinity, as indicated by a full width at half maximum of the X-ray diffraction peak of just 0.03°, but also achieve an optimal film thickness nonuniformity of 1.66 %. Our results offer valuable insights for the wafer-scale fabrication of AlN(100) films, potentially enhancing industrial production yields and reducing costs.

Dependence of the Nonuniformity of Thickness of the Vacuum-Arc Discharge Plasma Coating on the Geometric Parameters of the Inter-Blade Channel

Dependence of the Nonuniformity of Thickness of the Vacuum-Arc Discharge Plasma Coating on the Geometric Parameters of the Inter-Blade Channel

High-Q adiabatic micro-resonators on a wafer-scale ion-sliced 4H-silicon carbide-on-insulator platform.

A 4H-silicon carbide-on-insulator (4H-SiCOI) has emerged as a prominent material contender for integrated photonics owing to its outstanding material properties such as CMOS compatibility, high refractive index, and high second- and third-order nonlinearities. Although various micro-resonators have been realized on the 4H-SiCOI platform, enabling numerous applications including frequency conversion and electro-optical modulators, they may suffer from a challenge associated with spatial mode interactions, primarily due to the widespread use of multimode waveguides. We study the suppression of spatial mode interaction with Euler bends, and demonstrate micro-resonators with improved Q values above 1 × 105 on ion-sliced 4H-SiCOI platform with a SiC thickness nonuniformity less than 1%. The spatial-mode-interaction-free micro-resonators reported on the CMOS-compatible wafer-scale 4H-SiCOI platform would constitute an important ingredient for the envisaged large-scale integrated nonlinear photonic circuits.

Numerical modelling for retrieval of the coating thickness variations from wavefront errors measurements.

Multilayers coating are needed for large optical components performances, but the thickness non-uniformities over the useful aperture can generate spatial and chromatic variations of the reflectance, the transmittance and the wavefront errors. Although these dependences can be measured, they are difficult to anticipate if the underlying thickness variations are unknown. We present a model to retrieve these variations from wavefront error measurements that enables the computation of any optical properties over the useful aperture at any wavelength, angle of incidence or polarization.

Contribution of physical and system parameters in the determination of optical constants of thin solid phase samples using THz time domain transmission spectroscopy

Accurate estimation of complex refractive index of optically thin sample is an important challenge in terahertz time domain spectroscopy (THz-TDS). While majority of the previous studies on this topic consider Fabry-Perot (FP) effect as the primary cause of erroneous optical parameter extraction, advanced application criteria in industrial domains, such as, quality control of pharmaceutical composites or semiconductor heterostructure characterization etc. demand further assessment beyond FP effect only. Instead of conventional time-of-flight calculation pivoted to the reference data (usually obtained separately without any sample through air), we employed the differential data obtained from primary and secondary THz pulse through thin pellets to obtain accurate thickness mapping of the same. We observed that for pelletized samples with significantly larger porosity (>15%), the competing optical process like multiple internal scattering has greater impact on the accuracy of estimated optical properties. While in thin pelletized samples with smaller porosity (<10 %), the principal contributor of error is the non-uniform distribution of pellet thickness. For extremely thin pellets the optical parameter extraction is highly susceptible to uncertainties due to external factors such as environmental and/or system drift because of significantly small sample-THz interaction volume. Our observations indicate that short THz-sample interaction, porosity and non-uniformity of sample thickness are the principal causes of erroneous estimation of complex refractive index. It must be noted, however, that, this description does not specify an absolute value of material thickness but is highly dependent on the complex refractive index of the material itself. We also conclude that for specific material, there exists an optimized optical thickness beyond which the contribution of physical and system parameters in the determination of optical constants becomes minimal: it was determined to be around 3 mm for HDPE and 3.2 mm for PTFE. For most of the materials (with lower values of real and complex parts of optical constant) suitable for THz-TDS transmission spectroscopy, this critical thickness for accurate determination of the optical constant, therefore, is expected to be substantial, based on this present study.

Magnetron sputtering system for depositing boron carbide film use as neutron detection.

Boron carbide (B4C) films used as neutron conversion layers were investigated in this paper to replace the traditional 3He detectors due to their shortage. A magnetron sputtering system was developed for depositing large-size B4C films with the 1500 × 400mm2 uniform-area. B4C films at the micron scale were deposited on aluminum (Al), float glass (SiO2), and silicon (Si) substrates with an inserting adhesion layer. The key characteristics, including surface morphology, thickness nonuniformity, purity, and neutron efficiency of B4C films, were characterized using atomic force microscopy, scanning electron microscopy, grazing incidence x-ray reflectivity, x-ray photoelectron spectroscopy, and neutron radiation metrology. The experimental results indicate that the deposition thickness nonuniformity across a 1500 × 400mm2 area was better than ±3%. The stoichiometric ratio of boron atoms and carbon atoms (B/C) is 5.18, with 6 at. % O and 0.79 at. % N concentrations. The measured neutron detection efficiency of a 3 µm 10B4C film for 25meV neutrons was 3.3 ± 0.3(sys)%, which is close to the simulated results (3.4%). The results show that the B4C neutron conversion layer is a promising substitute for 3He for neutron detection in the future.

A large area 100-channel PICOSEC Micromegas detector with time resolution at the 20 ps level

The PICOSEC Micromegas precise timing detector is based on a Cherenkov radiator coupled to a photocathode operating in a semi-transparent mode and a Micromegas amplification structure. The first proof of concept single-channel prototype was able to achieve a time resolution below 25 ps. One of the crucial aspects in the development of precise timing gaseous detectors applicable in high-energy physics experiments is a modular design that enables large area coverage. The first 19-channel multi-pad prototype with an active area of approximately 10 cm2 suffered from degraded timing resolution due to the non-uniformity of the preamplification gap thickness. A new 100 cm2 detector module with 100 channels based on a rigid hybrid ceramic/FR4 Micromegas board for improved drift gap uniformity was developed. Initial measurements with 80 GeV/c muons showed improvements in timing response over the measured pads and a time resolution below 25 ps. More recent measurements with a thinner drift gap detector module and newly developed RF pulse amplifiers show that the pad centre resolution can be enhanced to the level of 17 ps. This work will present the development of the detector from structural simulations, design, and beam test commissioning with a focus on the timing performance of a thinner drift gap detector module in combination with new electronics using an automated timing scan method.

An Effect of Layered Auxiliary Cathode on Thickness Uniformity in Micro Electroforming Process.

Thickness nonuniformity is a bottleneck in the micro electroforming process of micro-metal devices. In this paper, a new method of fabricating a layered auxiliary cathode is proposed to improve the thickness uniformity of a micro-electroforming layer. In order to analyze the general applicability of the proposed method, four basic microstructures, namely circular, square, regular triangular, and regular hexagonal were used to study the effect of a layered auxiliary cathode on thickness uniformity through simulation and experimentation. The simulation results showed that with the help of the proposed auxiliary cathode, the thickness nonuniformity of four microstructures should decrease due to the reduced edge effect of the current density. The experimental results showed that the thickness uniformity of four microstructures fabricated via the proposed method was improved by 190.63%, 116.74%, 80.43%, and 164.30% compared to that fabricated via the traditional method, respectively. Meanwhile, the micro-gear was fabricated and the nonuniformity was reduced by 101.15% using the proposed method.

Realistic finite element analysis model of the pilgering process to deal with initial tube thickness nonuniformity

Traditional finite element analysis (FEA) models for simulating the pilgering process, based on the assumption of a fixed rigid mandrel and uniformity of the initial tube thickness, have practical disadvantages in solving industrial problems due to tube thickness nonuniformity and related mandrel deformation. A novel FEA model of the pilgering process with initial tube nonuniformity is presented herein, using an implicit elasto-thermoviscoplastic finite element method (FEM) with tetrahedral MINI-elements and multi-body treatment scheme, with an emphasis on the moveable and deformable mandrel and practical boundary conditions for the tube material. The effects of the number of layers in the radial direction on the predictions are investigated. The variation in thickness ratio with stroke during the pilgering process is predicted. It has been shown that the pilgering process considerably improves tube eccentricity.

Polishing and Local Planarization High-Precision HDC Capsules by Four-Cup-Type Technology for Inertial Confinement Fusion

In inertial confinement fusion (ICF) experiments, high-density carbon (HDC) is being evaluated as an alternative to the current point-design ablator material (glow discharge plasma) due to its high density and optimal opacity, which leads to a higher energy efficiency and implosion stability. Chemical vapor deposition–coated HDC capsules have a near-perfect surface figure but a microscopically rough surface, so polishing is needed to achieve the required nanometer surface finish. Herein, HDC capsule polishing is investigated with modified four-cup-type polishing technology. The surface morphology, microstructures, and wall thicknesses of the polished capsules were examined by multiple techniques, such as an optical microscope, scanning electron microscope, X-ray radiography, and so on. The results show that the HDC capsules can be polished to a surface roughness less than 15 nm and a wall thickness nonuniformity of about 0.5 μm. The Raman spectra indicated that four-cup polishing had no obvious influence on the original surface crystallinity and phase composition of the HDC capsules. The crystallographic of the HDC capsules with different four-cup polishing times had no deterioration. This work plays an important role for the application of HDC capsules in ICF research.

Improving the Thickness Uniformity of Micro Gear by Multi-Step, Self-Aligned Lithography and Electroforming.

The thickness nonuniformity of an electroformed layer is a bottleneck problem for electroformed micro metal devices. In this paper, a new fabrication method is proposed to improve the thickness uniformity of micro gear, which is the key element of various microdevices. The effect of the thickness of the photoresist on the uniformity was studied by simulation analysis, which showed that as the thickness of the photoresist increased, the thickness nonuniformity of the electroformed gear should decrease due to the reduced edge effect of the current density. Differently from the traditional method performed by one-step front lithography and electroforming, multi-step, self-aligned lithography and electroforming are used to fabricate micro gear structures in proposed method, which intermittently keeps the thickness of photoresist from decreasing during processes of alternate lithography and electroforming. The experimental results show that the thickness uniformity of micro gear fabricated by the proposed method was improved by 45.7% compared with that fabricated by the traditional method. Meanwhile, the roughness of the middle region of the gear structure was reduced by 17.4%.

New precision electroforming process for the simultaneous improvement of thickness uniformity and microstructure homogeneity of wafer-scale nanotwinned copper arrays

Nanotwinned (nt) Cu has received much attention because of its superior mechanical and electrical properties, but only a few production processes can yield nt-Cu parts with uniform thickness and a homogeneous microstructure on the wafer scale. To solve this problem, a new precision electroforming process is proposed that combines auxiliary cathodes with pulse reverse current (PRC) electroforming, which provides a synergistic effect to increase the homogeneity of the thickness and a nanoscale twin structure. As a practical example of the proposed process, 4-inch nt-Cu lamina arrays were fabricated and numerically modeled to probe into the synergistic mechanisms. The intrinsic correlations among the array element spacing, current waveform, and main forms of thickness nonuniformity were determined. In addition, the effects of the processing parameters on the microstructural evolution and microhardness of the nt-Cu arrays were analyzed. The results indicated that such a significant improvement in thickness uniformity and microstructure homogeneity were due to the auxiliary-cathode/PRC combination, which enables maximization of the PRC leveling efficiency by inducing a uniform current distribution; this effectively ensures that the microstructures are uniform across all laminae on the wafer scale. Additionally, thick nt-Cu deposited on the current-crowding regions was preferentially stripped during the application of reverse current. This alleviates the adverse effects of the current redistribution resulting from the auxiliary cathode on the thickness uniformity of the laminae and offers additional possibilities for homogeneous growth of nt-Cu. The new precision electroforming process has significant potential to produce wafer-scale components with uniform thickness and specific microstructures.

A novel broken wire evaluation method for bridge cable magnetic flux leakage testing under lift-off uncertainty

Magnetic flux leakage (MFL) is one of the most commonly used techniques for detecting broken wires of bridge cables. In practical testing, the sensor and magnetizer lift-off variations caused by mechanical vibration, sheath surface roughness and thickness nonuniformity significantly affect the accuracy of the estimated defect size. To address this problem, the theory of ratio of adjacent peaks (RAP) is developed based on the magnetic dipole model, which reveals the nonlinear relationship between RAP vector and broken-wire width. Based on the RAP theory, a radial sensor array (RSA) configuration and an evaluation method are further proposed in this paper. The RSA consists of four sensors along the bridge cable radial direction with a fixed interval and is employed to acquire RAP vector, which is identified as a spatial characteristic of MFL signal. An artificial neural network (ANN) algorithm is employed to develop the nonlinear defect width evaluation method based on the RAP vector. The effectiveness of the RSA configuration and the evaluation method is verified by finite element method (FEM). The results indicate that the broken-wire width can be accurately estimated utilizing RAP vector obtained by RSA without considering the lift-off variation.

Novel wafer-scale adhesive bonding with improved alignment accuracy and bond uniformity

We report a versatile method for improving post-bonding wafer alignment accuracy and BCB thickness uniformity in stacks bonded with soft-baked BCB. It is based on novel BCB-based micro-pillars that act as anchors during bonding. The anchor structures become a natural part of the bonding interface therefore causing minimal interference to the optical, electrical and mechanical properties of the bonded stack. We studied these properties for fixed anchor density and various anchor heights with respect to the adhesive BCB thickness. We demonstrated that the alignment accuracy can be improved by approximately an order of magnitude and approach the fundamental pre-bond alignment accuracy by the tool. We also demonstrated that this technique is effective for a large range of BCB thicknesses of 2–16 μm. Furthermore we observed that the thickness non-uniformities were reduced by a factor of 2–3 × for BCB thicknesses in the 8–16 μm range.

Preparation and Structural Investigation of Ultra-Uniform Mo Films on a Si/SiO2 Wafer by the Direct-Current Magnetron Sputtering Method

As a kind of important strategic resource, molybdenum (Mo) and its alloys are widely applied in solar cells and 5G radio frequency filters. In order to improve the yield of industrial production, it is important to reduce the nonuniformity of thin-film thickness. We prepared Mo films on CMOS compatible Si/SiO2 wafers through a magnetron sputtering method and systematically investigated the effect of tuning of several process parameters on film thickness nonuniformity and other structural properties, including crystallite size (D), microstrain (ε), and dislocation density (δ). At optimized sputtering power (80 W), chamber pressure (0.4 Pa), argon flow rate (90 sccm), substrate temperature (350 °C), and target–substrate distance (9 cm), the deposited 200 nm-thick Mo films show a unified <110> preferred orientation, and the film thickness nonuniformity reaches an excellent value of 0.46%, with a surface roughness of 0.83 nm and the full width at half maximum (FWHM) of X-ray diffraction (XRD) (110) rocking curve as low as 0.47°. Our results provide efficient reference for the preparation of uniform metal films, which have potential for improving the quality and yield in filter device manufacturing.