Auxiliary Cathode Research Articles

Fiber laser irradiation in chemical solution for micro fabrication: Mechanisms and applications

The laser and electrochemical hybrid machining (LECM) could realize high-efficient and quality processing of difficult-to-cut materials and has become a research topic in microfabrication. However, it was difficult to ensure the stability and efficiency of laser transmission in chemical solutions, and an external voltage and auxiliary cathode should be added. In the present study, a novel fiber laser irradiation in chemical solution (LICS) has been proposed to process microstructures. The surface microstructures and chemical composition of the surfaces processed by LICS, laser irradiation in the ultrapure water, and electrochemical machining were compared. In LICS the materials were removed by laser processing and the following high-temperature gradient induced electrochemical dissolution. The high temperature gradient induced electrochemical dissolution could enhance the MRR and improve the surface quality. LICS can be regarded as a novel LECM process. The machining efficiency of LICS had been improved by 46.2 % compared with that laser irradiation in the ultrapure water, and the proportion of laser-induced electrochemical dissolution was 31.6 % in the LICS process. Further, the effects of laser power, chemical solution concentration, and optical fiber end movement control on the processing of micro grooves were explored, considering the dimension, MRR, and surface roughness. A front gap of smaller than 0.8 mm between the optical fiber end and workpiece was recommended during LICS. The repeated feeding of optical fiber was proposed to improve the depth-to-width ratio of the micro grooves fabricated by LICS. Finally, LICS was used to process microstructures with the controlled profiles on the nickel-based superalloy and titanium alloy workpieces without a recast layer, which holds great potential in surface microfabrication and texturing.

Simulation and Optimization of the Auxiliary Cathode for Inter-Electrode Discharge Electric Field in Microarc Oxidation.

Currently, research on the edge effect issue in the micro-arc oxidation process primarily focuses on investigating process conditions and enhancing additives. However, some scholars have utilized finite element analysis software to simulate the edge effect during the simulation process, overlooking the investigation of the morphology of the auxiliary cathode. This study analyzes the growth characteristics of the oxide film on aluminum alloy 2A12 during micro-arc oxidation. Additionally, the inter-electrode discharge electric field is simulated using the finite element analysis method. The auxiliary cathode is optimized to mitigate the influence of the edge effect on the film layer. The findings indicate that employing a cylindrical shape as the auxiliary cathode instead of a rectangular groove leads to an increased thickness of the micro-arc oxidation film. However, it also results in an augmented length of the film layer affected by the edge effect at both ends of the workpiece. Decreasing the distance between the auxiliary cathode and the workpiece surface leads to a higher thickness of the obtained micro-arc oxidation film. Decreasing the length of the auxiliary cathode results in a reduction in both the thickness of the film layer on the workpiece surface and the area affected by the edge effect. Increasing the eccentric cone ratio of the auxiliary cathode enhances the uniformity of the micro-arc oxidation film layer. In this study, we present a novel auxiliary cathode model that incorporates a smaller cylindrical shell at the center and eccentric cone shells on each side. This model has the potential to enhance the optimization rate of the micro-arc oxidation film layer on cylindrical workpieces by 17.77%.

Effect of the auxiliary cathode on the thickness of the HiPIMS TiAlN coating deposited on the inner surface of the tube

The paper is focused on influencing the thickness of the TiAlN layer deposited using the high power pulse magnetron sputtering (HiPIMS) method on the inner surface of the tube. The HiPIMS method makes it possible to deposit layers at temperatures up to 400°C. An auxiliary cathode placed in the axis of the coated tube was used. The auxiliary cathode made it possible to deposit an AlTiN layer with a thickness in the center of the coated tube up to 45% higher compared to the thickness of the layer deposited without an auxiliary cathode.The layer thickness was measured to be from 1.5 µm to 2.2 µm for the layer deposited without an auxiliary cathode and 1.05 µm to 1.95 µm for the layer deposited with the wire as the cathode in the axis of the coated tube. Adhesion of the evaluated layers showed the degree of HF2 at the measured thickness points.

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.

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.

Improvement of Surface Quality for Titanium Alloys During Counter-Rotating Electrochemical Machining Using an Auxiliary Cathode

Counter-rotating electrochemical machining (CRECM) is an innovative ECM method that can be used to manufacture revolving parts, especially titanium alloy casings. Because titanium alloys are easily passivated metals, sufficient electrical quantity is required to achieve the transition from pitting to smoothing with a lower speed. However, a low rotational speed means more material is removed in a machining cycle, which is not conducive to wall thickness control. Therefore, achieving fast smoothing at a relatively high rotational speed for titanium alloys is focused. In this paper, the proposed methodology applies an auxiliary cathode to accelerate the transition from pitting corrosion to smoothness of titanium alloys at a relatively high rotational speed. Experimental results show that titanium alloy can be smoothed regardless of rotational speed with an auxiliary cathode. The auxiliary cathode can weaken the off-current density region and accelerate the breakdown of the oxide layer, and the layer-by-layer dissolution of micron-thick materials is achieved at a relatively high rotational speed. The grid-like convex structure is produced at a relatively high rotational speed with an auxiliary cathode, and the surface roughness is 1.808 μm. This fully demonstrates the reliability of the auxiliary cathode for achieving the smoothness of titanium alloys.

P‐20: High Quality Self‐Aligned Coplanar Thin‐Film Transistors with SOG Materials for High Transparent AMOLED Display

We improved the performance of self‐aligned coplanar thin‐Film transistors with SOG Materials. In this work, the composition of TFT's buffer layer was changed by SOG Material to ensure the electrical performance of TFTs and high transparency of panel simultaneously. In addition, the shielding metal layer of self‐aligned top gate TFT was used as auxiliary cathode which can improve the uniformity of large size AMOLED display. We achieved 48% transparency of AMOLED display panel with 80PPI resolution ratio.

7‐2: High Transmittance Under‐Display Camera Structure with COE

A novel under‐display camera structure with high transmittance up to 40.8% was proposed to increace transmittance, in which all pixel circuits and metal traces were moved to the transition zone which is right next to the UDC zone, and the circular polarizer was replaced with COE, and then the metal cathode is patterned by self‐assembly method, and the disconnected cathodes are connected together by transparent auxiliary cathode.

Si-DLC films deposited by a novel method equipped with a co-potential auxiliary cathode for anti-corrosion and anti-wear application

A novel DLC film deposition method was proposed to realize the deposition of DLC film on the surface of complex shaped workpiece. Meanwhile, Si-DLC film was deposited on the surface of M2 high-speed steel (HSS M2) and 304 stainless steel (304SS), and the microstructure, surface roughness, mechanical properties, corrosion resistance and tribological properties of Si-DLC films were characterized in detail. Results show that Si-DLC film at different axial positions of the auxiliary cathode possesses similar microstructure, film thickness and surface roughness, and the as-deposited Si-DLC film shows the low intrinsic stress of < 0.3 GPa. Compared with the 304SS substrate, the Si-DLC film presents more noble corrosion potential, lower corrosion current density and higher polarization resistance, exhibiting higher corrosion resistance. Moreover, the Si-DLC film exhibits higher hardness, elastic factor and plastic factor than HSS M2 substrate and the corresponding adhesive strength is more than 10 N. The Si-DLC film sliding against GCr15 steel ball shows a lower friction coefficient than that of HSS M2 substrate and the wear rate of GCr15 steel ball sliding against the Si-DLC is lower than that of HSS M2 substrate. In addition, this novel method was used to deposit Si-DLC film on gears, drills and bearings without rotating sample racks. As a consequence, this method possesses great potential and can be generalized for the deposition of DLC film on the surface of complex shape workpiece.

Operating an ozone-evolving PEM electrolyser in tap water: A case study of water and ion transport

While PEM water electrolysis could be a favourable technique for in situ sanitization with ozone, its application is mainly limited to the use of ultrapure water to achieve a sufficient long-time stability. As additional charge carriers influence the occurring transport phenomena, we investigated the impact of different feed water qualities on the performance of a PEM tap water electrolyser for ozone evolution. The permeation of water and the four most abundant cations (Na+, K+, Ca2+, Mg2+) is characterised during stand-by and powered operation at different charge densities to quantify underlying transport mechanisms. Water transport is shown to linearly increase with the applied current (95 ± 2 mmol A−1 h−1) and occurs decoupled from ion permeation. A limitation of ion permeation is given by the transfer of ions in water to the anode/PEM interface. The unstabilized operation of a PEM electrolyser in tap water leads to a pH gradient which promotes the formation of magnesium and calcium carbonates and hydroxides on the cathode surface. The introduction of a novel auxiliary cathode in the anolytic compartment has shown to suppress ion permeation by close to 20%.

Improved solution cathode glow discharge micro-plasma source with a geometrically optimized stainless steel auxiliary cathode for optical emission spectrometry of metal elements

An improved micro-plasma source for the quantitative analysis of heavy metal elements by solution cathode glow discharge-optical emission spectrometry (SCGD-OES) was developed. The glow-discharge plasma source was fabricated using a geometrically optimized stainless steel auxiliary cathode solution and a tungsten anode. Optimum discharge could be attained at reduced solution flow rates under the following operating conditions: pH 1.0 (HNO3); a discharge current of 80 mA; a solution flow rate of 1.65 mL/min; and a discharge gap of 2.5 mm. The detection limits (DLs) of the improved micro-plasma source for K, Na, Ni, Cd, Co and Hg were 0.17, 0.06, 18, 10, 25 and 66 μg/L, respectively. The recoveries of metal elements from spiked samples of spring river, Yangtze River and reservoir water measured by SCGD-OES showed good agreement with those obtained using ICP-OES. The results from this study may provide a new direction for the design of glow discharge sources for the in situ determination of metal elements in complex water samples.

Numerical Simulation of Optimizing Plating Uniformity of Interconnect Circuits on Printed Circuit Boards

Based on the finite element method, the interconnection circuit models with different pattern designs were established and plating copper circuits were simulated to obtain the plating uniformity. Meanwhile, the influence of insulating shield, auxiliary cathode and the distance between anode and cathode (DAC) on the plating uniformity is studied to provide theoretical guidance for improving the uniformity of electroplating copper at actual production. Compared with other pattern designs, the circuit with a pattern design area ratio of 20% has the best plating uniformity under the initial conditions. The increase in the auxiliary cathode width and the decrease the aperture of insulating shield and DAC can improve the electroplating uniformity of circuit.

Study on Controllable Thickness and Flatness of Wafer-Scale Nickel Shim in Precision Electroforming Process: Simulation and Validation

Abstract A new approach to precision electroforming of a wafer scale nickel shim using a rotating cathode with an auxiliary cathode mask is developed to improve thickness uniformity and flatness. The effects of critical process parameters, including cathode rotating speed, cathode mask size, and current density, on the thickness uniformity and flatness of electroformed nickel shim are systematically studied based on experiments and simulations. The results show that the thickness uniformity of the deposits is highly dependent on the current density distribution, where a cathode mask can effectively tune electrical field lines and induce a more uniform current density distribution. The simulations and experimental results consistently agree that a minimum thickness nonuniformity of 8% and below 1% on the wafer with a diameter of 80 mm and 40 mm, respectively, can be achieved using a mask with a 70 mm opening size. However, for flatness, the cathode rotating speed influences the surface warpage due to the intrinsic stress. It is also found that the gradient current density can significantly reduce the intrinsic stress with better flatness. The best flatness is controlled below 47 µm and 32 µm on the wafer with diameters of 80 mm and 40 mm, respectively, under the synergistic effect of optimal cathode rotating speed (30 rpm) and gradient current density.

P‐92: A 12.3‐in. Top‐Emission AMOLED Transparent Display

A 12.3‐inch top‐emission AMOLED transparent display based on LTPS TFT technology was developed. The transmittance of this novel display reached nearly 50% by adopting transparent area and pattern cathode. In addition, the design of auxiliary cathode can effectively reduce power consumption and improve reliability and lifetime of the panel.

Bio-inspired design of an auxiliary fishbone-shaped cathode flow field pattern for polymer electrolyte membrane fuel cells

A bio-inspired auxiliary fishbone-shaped flow field (AFFF) pattern is proposed and designed at the cathode flow field plate (FFP) of polymer electrolyte membrane (PEM) fuel cells, in order to enhance under-rib mass transport and water removal from gas diffusion layer (GDL). The bio-inspired AFFF pattern is numerically investigated by a three-dimensional multiphase fuel cell model. It is shown that the AFFF pattern significantly improves under-rib mass transport and water removal ability, hence fuel efficiency is improved. In comparison with the conventional parallel flow field (CPFF) pattern, the new pattern exhibits higher uniformity of reactants and saturation distributions, and thereby improving the operation stability of fuel cells. Furthermore, sub-branch channels of various numbers and widths in the AFFF pattern are evaluated with consideration of electrical contact resistance (ECR) between the FFP and GDL. Under-rib mass transport and water removal is improved when increasing the number and width of sub-branch channels. However, the ECR somehow increases as well. Therefore, counterbalance between under-rib mass transfer and ECR should be considered. Finally, the AFFF pattern with an optimized combination between number and width of sub-branch channels is achieved to improve the maximum power density of fuel cells.

Surface hardening of laser melting deposited 12CrNi2 alloy steel by enhanced plasma carburizing via hollow cathode discharge

Plasma carburizing of 12CrNi2 alloy steel fabricated by laser melting deposition was carried out in a propane-containing atmosphere at temperature of 930 °C with and without hollow cathode discharge (HCD). The generation of the HCD in the carburizing process was achieved by adding an auxiliary cathode opposite the alloy steel sample. The carburized samples were characterized by analysis of microstructure, microhardness and wear performance. The assistance of HCD increased the carbon concentration in the carburized layer and the case depth without changing the carburizing atmosphere and discharge voltage, indicating the improvement of carburizing kinetics. This leads to an increased volume fraction of acicular martensite and an increased the microhardness of the carburized layer as well as the improvement of the wear resistance of alloy steel.

Effect of auxiliary cathode on plasma nitriding behavior of Cr12MoV alloy steel

Cr12MoV alloy steel was nitrided in a plasma chamber with and without an auxiliary cathode. The results indicate, that at an appropriate distance between the auxiliary cathode and the alloy steel, hollow cathode discharge (HCD) is generated. The HCD is effective and important to harden the alloy steel by promoting the formation of a harder and thicker nitrided layer, which not only contains a nitrogen diffusion zone, where nitridation of the chromium carbide of the alloy occurs as in the case without auxiliary cathode, but also a top compound layer. The distance between the auxiliary cathode and the alloy steel noticeably affected the plasma nitriding kinetics of the Cr12MoV alloy steel. As the distance increases, the thickness of the compound layer and the microhardness of the nitrided layer increase first followed by a decrease. The nitridation mechanisms of the alloy steel with and without auxiliary cathode are discussed.

Fabrication of metal microfluidic chip mold with coplanar auxiliary cathode in the electroforming process

Thickness nonuniformity is one of the prominent problems in the electroforming process of the metal microfluidic chip mold, which decreases the dimensional accuracy of the mold, and has a direct influence on the usability of the microfluidic chip. A novel method of auxiliary cathode for improving the thickness uniformity of electroformed mold is presented in this paper. Compared with the traditional method of the auxiliary cathode, a coplanar auxiliary cathode similar to the local microstructure of mold is used to fabricate the electroformed mold, and the thickness uniformity of electroformed mold is improved obviously. In addition, in order to determine the dimensions and placement of the auxiliary cathode, the computer-aided analysis is performed to simulate electroforming process. The simulated results show that with the help of a specially designed auxiliary cathode, the thickness uniformity is improved by about 53.2% compared with the result without the auxiliary cathode. Finally, based on the simulation, a microfluidic chip mold is fabricated by micro electroforming with the coplanar auxiliary cathode. The result shows that the thickness uniformity of the mold is improved by about 49.1%, which is in good agreement with the simulation result.

Improvement of plating uniformity for copper patterns of IC substrate with multi-physics coupling simulation

PurposeOptimized plating conditions, included proper designs of insulating shield (IS), auxiliary cathode (AC) and different patterns, contribute to the uniformity enhancement of copper deposition.Design/methodology/approachPlating experiments were implemented in vertical continuous plating (VCP) line for manufacturing in different conditions. Multiphysics coupling simulation was brought to investigate and predict the plating uniformity improvement of copper pattern. In addition, the numerical model was based on VCP to approach the practical application.FindingsWith disproportionate current distribution, different plating pattern design formed diverse copper thickness distribution (CTD). IS and AC improved plating uniformity of copper pattern because of current redistribution. Moreover, optimized plating condition for effectively depositing more uniformed plating copper layer in varied pattern designs were derived by simulation and verified by plating experiment.Originality/valueThe comparison between experiment and simulation revealed that multiphysics coupling is an efficient, reliable and of course environment-friendly tool to perform research on the uniformity of pattern plating in manufacturing.

Spatial-Harmonic Magnetrons with Cold Secondary-Emission Cathode: State-of-the-Art (Review)

Spatial-harmonic magnetrons with cold secondary-emission cathode are efficient high-power sources throughout the millimeter wavelength band. In this paper, resent advances in design, modeling, and fabrication of such magnetrons are described. Low-voltage magnetrons, sub-THz tubes, and magnetrons with metamaterial anode structure are described to illustrate these advances. The issue of the lifetime of the magnetrons with a cold secondary-emission cathode is also addressed. The main problems related with the usage of an auxiliary cathode in such tubes are considered and alternative solutions are discussed. Potentials for further improving the performance of spatial-harmonic magnetrons are analyzed as well.