Increase In Contact Resistance Research Articles

Study on contact degradation of ARC contact of SF 6 circuit breaker for reactive switching

Frequent operation of SF6 circuit breaker for switching capacitor banks leads to radial loss and stress relaxation of arc contact, and contact degradation occurs, which seriously affects its performance and operating life. In order to study the influence of radial loss and stress relaxation on contact degradation of SF6 circuit breaker arc contact, this paper established a contact resistance model based on Holm theory, and obtained the relationship between radial loss and increase of contact resistance, then influence of arc contact stress relaxation on contact resistance was studied through theoretical calculations. Results show that contact resistance increases with the increase of radial loss of arc contact. When inrush current peak is 15kA, radial loss reaches 0.2366mm, and contact resistance increases by 54μΩ. At the same time, it is found that stress relaxation during long-term deformation will lead to a decrease in contact force. It is predicted that stress loss will be close to 40% of initial stress after 20 years, and stress relaxation will increase contact resistance by 50μΩ.

Controlled Hydride Formation on Titanium Porous Transport Layer for Application in PEM Water Electrolysis

Titanium belongs to a group of valve metals that are known to possess a surface layer of passive oxide that protects the material from corrosion. Thanks to this attribute, titanium can withstand even harsh conditions prevailing in the anode compartment of PEM water electrolyzer. This makes titanium, together with its high electrical conductivity, a suitable material for the anode porous transport layer (PTL) and the bipolar plates in PEM water electrolyzers. However, too extensive passivation leads to an increase of contact resistance between the PTL and catalyst layer and consequently decreases the energy efficiency. This is the reason why titanium PTL is usually covered with a thin coating of precious metal (such as iridium or platinum) [1]. This thin coating hinders further titanium oxidation during electrolyzer operation and mediates good electrical contact with the catalyst particles. Recently, a much cheaper alternative approach based on titanium surface etching in acid has been introduced [2]. Titanium hydride that forms during this treatment has been shown to inhibit the passive layer growth, thus decreasing the contact resistance and improving the energy efficiency of the electrolysis.This work aims to further develop the ideas presented in reference [2] and investigate the role of titanium hydride during PEM water electrolysis. The hydridation treatment was done on pieces of titanium foil and consists of two steps. The first step is etching in boiling 35% HCl. This step removes the native oxide layer, increases the surface roughness, and introduces some amount of hydrogen into the crystal lattice of the metal. The second step involves cathodic polarization of the etched samples allowing more pronounced hydridation.By changing the condition of the cathodic polarization process, it is possible to tune the hydrogen uptake. The effects of polarization time, current density, temperature and concentration of electrolyte were studied with respect to the amount of the hydride layer formed, its thickness and penetration into the bulk phase. Treated titanium foils were characterized by various physicochemical techniques. X-ray diffractometry was used for hydride quantification, further analysis was done by scanning electron microscopy and cross-sectional metallography. Electrochemical properties of samples were studied by impedance spectroscopy and linear sweep voltammetry.The hydridation procedure was then used for titanium PTLs treatment which were then tested at the anode side of the PEM water electrolyser. Significant increase of current density was observed for etched and polarized Ti PTLs in comparison with pristine Ti PTL (Figure A). This can be attributed to significantly decreased contact resistance of treated PTLs (Figure B). A further performance increase was achieved when PTLs were treated prior to iridium coating (Figure A, B). It is thus possible to conclude, that the hydridation represents a promising approach to reduce precious metals demands in PEM water electrolysis construction.Financial support by the Czech Science Foundation within the framework of the project No.: 20-06422J is gratefully acknowlegded. Liu, C., et al., Exploring the Interface of Skin-Layered Titanium Fibers for Electrochemical Water Splitting. Advanced Energy Materials, 2021. 11(8): p. 2002926. Bystron, T., et al., Enhancing PEM water electrolysis efficiency by reducing the extent of Ti gas diffusion layer passivation. Journal of Applied Electrochemistry, 2018. 48(6): p. 713-723. Figure 1

Novel silver-enhanced hard gold electrodeposit applied for electrical contacts: comparison with conventional gold–cobalt alloy

ABSTRACT An Au–Ag coating has been envisaged as an alternative to the conventional Au–Co electrodeposit. In this study, an Au–Ag coating was electrodeposited on Cu substrates pre-coated with a Ni layer. The contact resistance of the Au–Ag coating was observed to be lower than that of the Au–Co coating. Under extended aging, the Au–Ag coating demonstrated a slightly increased contact resistance, while the contact resistance of the Au–Co coating increased significantly. Additionally, the solderability of the Au–Ag coating surpassed that of the Au–Co coating. Qualitative analyses demonstrate that, in the case of Au–Co coating, a considerable amount of Ni diffused through the Au layer to react with O2 in the air to form oxides during aging. The Co elements also oxidised due to aging. The formation of the oxide layer induced an increased contact resistance and diminished solderability. In addition, the Au–Co coating consisted of finer grains than the Au–Ag coating, promoting the Ni diffusion through the Au layer.

Refractory metal-based ohmic contacts on β -Ga2O3 using TiW

The present work investigates the use of the refractory metal alloy TiW as a possible candidate for the realization of ohmic contacts to the ultrawide bandgap semiconductor β-Ga2O3. Ohmic contact properties were analyzed by transfer length measurements of TiW contacts annealed at temperatures between 400 and 900 °C. Optimum contact properties with a contact resistance down to 1.5 × 10−5 Ω cm2 were achieved after annealing at 700 °C in nitrogen on highly doped β-Ga2O3. However, a significant contact resistance increase was observed at annealing temperatures above 700 °C. Cross-sectional analyses of the contacts using scanning transmission electron microscopy revealed the formation of a TiOx interfacial layer of 3–5 nm between TiW and β-Ga2O3. This interlayer features an amorphous structure and most probably possesses a high amount of vacancies and/or Ga impurities supporting charge carrier injection. Upon annealing at temperatures of 900 °C, the interlayer increases in thickness up to 15 nm, featuring crystalline-like properties, suggesting the formation of rutile TiO2. Although severe morphological changes at higher annealing temperatures were also verified by atomic force microscopy, the root cause for the contact resistance increase is attributed to the structural changes in thickness and crystallinity of the interfacial layer.

A new thermal conductivity relational expression for polymer composites with constructal design fillers

Constructal law is usually used to optimize the heat transfer enhancement of fillers. The filler with constructal design is easy to form the heat conductive path, so the composite with constructal fillers has high thermal conductivity. However, existing relational expressions cannot reveal the performance of heat transfer enhancement for constructal fillers. In this work, a new relational expression is established to reveal above coupled mechanism and calculate the thermal conductivity of composite with constructal fillers. The filler shape effect the strengthening mechanism of the thermal conductivity ratio. The critical values of the thermal conductivity ratio are round 150, 300, 600, 700 and 950 for rhombic, elliptical, I shaped, T shaped and rectangular fillers. With the increase of the thermal contact resistance, the thermal conductivity of composite will pass through three typical stages: very slow decrease, sharp decrease, and maintained stability. To improve the thermal conductivity of composite by decreasing the thermal contact resistance should be at the second stage (10−4 < thermal contact resistance <0.2). Meanwhile, the effect of filler shape on the thermal conductivity will be decreased with the thermal contact resistance.

P‐22: Effects of Self‐Assembled Monolayer on Contact Resistance Between IGZO and Electrode for High‐Resolution Display

We improved the contact properties by inserting a self‐assembled monolayer at the interface between a‐IGZO and metal electrode. For high‐resolution and high‐speed displays, the transistor channel length needs to be reduced without short channel effects. In case of Al electrode, it easily diffuses into a‐IGZO and forms AlOx at the interface, resulting in a considerable contact resistance increase. In our approach, we successfully suppressed Al diffusion by self‐assembled monolayer treatment on a‐IGZO thin film. The thickness of AlOx was significantly reduced, which was verified by transmission electron microscopy images. With a proper self‐assembled monolayer treatment, the contact resistance was decreased by 36%.

The Effect of the Surface Roughness Characteristics of the Contact Interface on the Thermal Contact Resistance of the PP-IGBT Module

In this article, the correlation between the thermal contact resistance and the surface roughness characteristics of the contact interface in the press-pack insulated-gate bipolar transistor (PP-IGBT) modules during power cycling was studied by experimental measurements and finite-element (FE) simulation-based factorial design analysis. Thermal transient test technology was applied to examine the change in the thermal characteristic parameters of the PP-IGBT module. This shows that the increase in the thermal contact resistance of the Al metallization/emitter Mo contact interface occurs more dramatically during power cycling. A 3-D surface profilometer was used to evaluate the surface morphology parameters of the Al metallization/emitter Mo contact interface. The equivalent root-mean-square (RMS) roughness increases during power cycling, and the equivalent asperity slope and the equivalent spacing between asperities increase slightly. Additionally, the surface roughening in the corner area of the chip is more obvious than in other regions. A fractional factorial design analysis based on FE simulations was performed. The results indicate that the thermal contact resistance strongly depends on the main effects of the real contact area and the spacing between the asperities, and the RMS roughness and the asperity slope interaction.

High-performance bulk heterojunction-based photocathode with facile architecture for photoelectrochemical water splitting

Organic semiconductors are promising candidates as photoactive layers for photoelectrodes used in photoelectrochemical (PEC) cells due to their excellent light absorption and efficient charge transport properties with the help of interfacial materials. However, the use of multilayers will make the charge transfer mechanism more complicated and decrease the PEC performance of the photoelectrode caused by the increased contact resistance. In this work, a PM6:Y6 bulk heterojunction (BHJ)-based photocathode is fabricated for efficient PEC hydrogen evolution reaction (HER) in an acidic aqueous solution. With RuO2 as an interfacial modification layer, the photocathode with a simple structure (fluorine-doped tin oxide (FTO)/PM6:Y6/RuO2) generates a maximum photocurrent density up to −15 mA/cm2 at 0 V vs. reference hydrogen electrode (RHE), outperforming all previously reported BHJ-based photocathodes in terms of PEC performance. The highest ratiometric power-saved efficiency of 3.7% is achieved at 0.4 V vs. RHE.

Research on the electric life evaluation technology of the arc extinguishing chamber of the 550 kV circuit breaker

When the circuit breaker is switched on and off, the phenomenon of arc ablation will occur. Under the action of the electric arc, the surface of the contact is constantly damaged, resulting in deformation and material evaporation. With the increase in the electric arc temperature, the material loss on the contact surface of the circuit breaker increases. In this paper, according to the three major factors affecting the electrical life of the circuit breaker arc extinguishing chamber—the state of the arc contact, the nozzle, and the SF6 gas—the corresponding test detection methods and evaluation methods are proposed. With the continuous accumulation of the breaking current, the effective contact displacement between the arc contacts decreases and the average contact resistance increases. The effective contact displacement decreases exponentially with the increase in the cumulative breaking energy. The content of CF4 can be used not only to characterize the discharge ablation on the surface of the nozzle insulating material but also to characterize the discharge decomposition degree of SF6 in the system by adding carbonaceous compounds. Through the experiment, it is suggested that CF4 should reach 600 µl/l as the threshold for judging whether the arc extinguishing chamber needs maintenance. This method can be extended to the working condition evaluation of the arc extinguishing chamber of other types of the SF6 circuit breaker.

Study on Fault Optimization of Intermediate Joint of Power Cable

Abstract Cable joints are often prone to failure due to loose contact, small contact area and increased contact resistance, resulting in obvious heating. In the existing cable emergency repair work, the cable joints of the original section of the cable and the access end are made on site. Due to the long production time, the emergency repair speed is reduced. Therefore, this paper studies the connection mode of the new cable joint to make the contact between conductors more sufficient and the contact resistance smaller, and designs a scheme of three-phase cable plug-in intermediate joint with high safety and simple installation; at the position of cable joint, three kinds of flexible conductive polymer materials suitable for joint connection are proposed to be used at the contact gap between conductor and conductor, conductor and conductor sleeve, so as to make close contact, reduce contact resistance and further reduce the incidence of cable joint failure.

An imperfect thermal contact problem for consolidation of bilayered saturated soil subjected to ramp-type heating

This study proposes a generalized imperfect thermal contact model to simulate the thermal contact resistance existing at the interface between the two adjacent soil layers. Based on the generalized imperfect thermal contact model, a thermo-hydro-mechanical (THM) coupled consolidation model for bilayered saturated soil under ramp-type heating load is established. By means of the Laplace transform, the semi-analytical solutions of temperature increment, excess pore water pressure and displacement of the bilayered saturated soil are obtained. Based on the present solutions, the THM coupled consolidation behaviors are investigated through comparative and parametric analysis. The results show that the generalized imperfect thermal contact model can realistically describe the imperfect thermal contact problem and can be degenerated into other commonly-used thermal contact models. Due to the existence of interfacial thermal contact resistance, only a portion of heat flux passes through the interface, weakening the influence of the thermal load on the consolidation behaviors of non-heated layer. With the decrease of contact transfer coefficient and the increase of partition coefficient, the interfacial thermal contact resistance increases, and the influence of the thermal conductivity of soil grains reduces.

Analysis of Cr/Au contact reliability in embedded poly-Si micro-heater for FET-type gas sensor

Gas sensors with micro-heaters are being widely studied in various fields. However, there are few systematic studies examining the effect of embedded heaters on their reliability and gas detection features. In this work, we investigate the change in electrical characteristics of the heater that occurs when thermal stress and current stress are applied to the embedded micro-heater for the FET-type gas sensor. Four different patterns of micro-heaters exhibited the same resistance change. Also, we investigate the effect of the increase in contact resistance between the poly-silicon heater and the metal (Cr/Au) electrodes on the gas sensing characteristics. As the heater resistance increases by 12%, the power consumption for optimal gas response increases by 58%, and the gas response is reduced by 46% without compensation of the heater voltage. The result indicates that the heating efficiency of the poly-silicon heater also changes during the degradation of the heater. The reason for the increase in the heater resistance and the change in the heating efficiency is explained by the inter-diffusion of Cr atoms to the surface through the Au layer. The diffusion of Cr atoms is confirmed by TEM and EDS analysis in the contacts at both ends of the heater. The results suggest that the temperature at the same voltage applied across the heater should also be considered in the reliability of the sensor platform.

Performance and reliability improvement in intercalated MLGNR interconnects using optimized aspect ratio

In this work, aspect ratio of various intercalation doped MLGNR interconnects are optimized using a numerical approach to achieve improved performance and reliability. A numerical optimization method is presented to estimate optimized aspect ratio considering combined effects of performance, noise and reliability metrics for any arbitrary nano interconnect system. This approach is cost effective and will be extremely useful to industry for selection of aspect ratio of interconnects as it is a non-SPICE method and reduces fabrication iterations for achieving desired performance and reliability. Our numerical method suggests that by minimizing the figure of merit (i.e. Noise Delay Power Product / Breakdown Power P_{BD} ratio), aspect ratio of FeCl3 doped MLGNR interconnect is optimized at 0.987, 0.61 and 0.579 for local, intermediate and global level, respectively at 7 nm node. Comparing the optimized performance metrics in this work with the estimated metrics at prescribed aspect ratio by IRDS roadmap, delay, noise delay product (NDP), power delay product (PDP), PDP/ P_{BD} ratio and figure of merit are improved by (sim2% and sim25%), (sim44% and sim50%), (sim9% and sim48%), (sim6% and sim48%) and (sim49% and sim68%) for 10 mu m and 1 mm long Fecl3 doped MLGNR interconnect, respectively at 7 nm node. Increase in contact resistance leads to significant decrease in performance and increase in optimized aspect ratio of local Fecl3 doped MLGNR interconnect. Scaling down from 10 to 7 nm node results in increase of optimized aspect ratio in all levels of interconnects. Even though the performance of MLGNR degrades with scaling down but when compared to copper, the performance improves with technology scaling. Finally, this study provides circuit designers a detailed guideline for selecting an optimized aspect ratio for achieving better performance, power efficiency and reliability in doped MLGNR interconnects.

Influence of Injection Barrier on Vertical Organic Field Effect Transistors

Organic field-effect transistors (OFETs) have shown great potential for applications that require low temperature deposition on large and flexible substrates. To increase their performance, in particular a high transconductance and transit frequency, the transistor channel length has to be scaled into the submicrometer regime, which can be easily achieved in vertical organic field effect transistors (VOFETs). However, despite high performance observed in VOFETs, these transistors usually suffer from short channel effects like weak saturation of the drain current and direct source-drain leakage resulting in large off currents. Here, we study the influence of the injection barrier at the source electrode on the OFF currents, on/off ratio, and transconductance of vertical OFETs. We use two semiconducting materials, 2,6-diphenyl anthracene (DPA), and C60 to vary the injection barrier at the source electrode and are able to show that increasing the Schottky barrier at the source electrode can decrease the direct source/drain leakage by 3 orders of magnitude. However, the increased injection barrier at the source electrode comes at the expense of an increased contact resistance, which in turn will decrease its transconductance and transit frequency. With the help of a 2D drift-diffusion simulation we show that the trade-off between low off currents and high transconductance is inherent to the current VOFET device setup and that new approaches have to be found to design VOFETs that combine good switching properties with high performance.

Дугостойкость на воздухе сплавов WС – Cr3С2 – Сu с бескаркасной упаковкой карбидов

In this work, the arc resistance of electrical contacts of the compositions WC – Cu, Cr3C2 – Cu and WC – Cr3C2 – Cu (with a mass ratio of WC:Cr3C2 = 1:1) was studied in comparison with the industrial contact D30V70, and an analysis was made of the dependence of functional properties on the composition and contact structures. Experimental samples of electrical contacts were obtained by liquid-phase impregnation of non-compacted carbide powders with copper at low-frequency (~ 80 Hz) vibration of the crucible with alloy components for 10 min in a resistance furnace in an atmosphere of flowing argon. Prepared samples were tested using equipment that simulated the operation of an AC contactor (170 A, 50 V, 1000 – 10000 arcing cycles). Their functional properties (hardness, arc wear, contact resistance) have been studied. The evolution of the structure was studied using optical and electron microscopy. It is shown that alloys containing WC or WC + Cr3C2 have stable values of contact resistance (up to 10,000 arcing cycles). Alloy WC57Cu43 (wt. %) has the highest arc resistance, which is not only comparable with the industrial alloy, but also surpasses it in long-term tests, despite the lower content of the arc-resistant phase. In contacts of the Cr3C2 – Cu composition, the contact resistance increases and grows most sharply after 4000 arcing cycles. In contacts made of bicarbide alloy WC – Cr3C2 – Cu, the degree of increase in contact resistance is similar to the industrial alloy, but the average values are higher. The wear layers of monocarbide alloys are highly oxidized. In a bicarbide alloy, there is no oxygen in the composition of such a layer. The composition of this alloy is represented by solid solutions of metals and their carbides, and the structure is finely dispersed. The mechanisms of arc resistance in electrical contacts of various compositions are discussed.

Effects of cobalt deposition and pretreatment process on electrical properties of products

The preferable conditions for formation of high quality CoSi2 films and effect of process parameters on properties of products were investigated. The pretreatment should not only remove the natural oxide layer completely, but also could not damage Si substrate. The good static random access memory (SRAM) proportion of products is high when pretreatment thickness is 20 Å, reached 96.5%. The radio frequency (RF) bias power process parameter should also take an optimal value. When RF bias power is 150 W, the good SRAM proportion of products is greater than 98%. The 100 Å Co can just completely react with Si substrate after twice annealing (500 °C 30 s and 750 °C 30 s), and if it exceeds 100 Å, Co will be residual. Decreasing Co thickness leads to contact resistance (RC) increase whatever in N-well or P-well. The overall standby current (Isb) of product is least when Co thickness is 80 Å. Finally, the products achieved good electrical properties when Co thickness is 80 Å, pretreatment thickness is 20 Å and RF bias power is 150 W.

A Platinum Micro-Reference Electrode for Impedance Measurements in a PEM Water Electrolysis Cell

We present a platinum wire micro-reference electrode (Pt-WRE) suitable for recording individual electrochemical impedance spectra of both the anode and the cathode in a proton exchange membrane water electrolyzer (PEM-WE). For this purpose, a thin, insulated Pt-wire reference electrode (Pt-WRE) was laminated centrally between two 50 μm Nafion® membranes, whereby the potential of the Pt-WRE is determined by the ratio of the local H2 and O2 permeation fluxes at the tip of the Pt-WRE. Impedance analysis with the Pt-WRE allows determination of the proton sheet resistance of the anode, the anode catalyst layer capacitance, and the high-frequency resistance (HFR) of both electrodes individually, using a simple transmission-line model. This new diagnostic tool was used to analyze performance degradation during an accelerated stress test (AST), where low and high current densities were alternated with idle periods without current (i.e., at open circuit voltage (OCV)), mimicking the fluctuating operation of a PEM-WE with renewable energy. Our analysis revealed that the increasing HFR that was observed over the course of the OCV-AST, which is the main cause for the observed performance decrease, can unequivocally be assigned to an increasing contact resistance between the anode electrode and the porous transport layer.

Tribodynamic studies of textured gearsets lubricated with fresh and MoS2 blended greases

The synergistic effects of surface texture and Molybdenum disulphide (MoS2) blended grease have been explored on the tribodynamic performance of spur gearsets. A texture involving ellipsoidal dimples on the face and flank of pinions’ teeth was fabricated using nanosecond pulsed fiber laser. The experiments were performed at different applied torques and a pitch line velocity of 4 m/s keeping in mind the practical application of the results. Contact resistance, vibrations, temperature rise and surface topographies have been measured and analyzed. Substantial increase (about 300%) in contact resistance and reduction (40% approximately) in vibration amplitudes at gear mesh frequency were found in the presence of texture. Reduction in interfacial temperature rise and less damage to teeth surface were also observed.

Influence of film morphology and crystallinity on charge carrier concentration-dependent hole mobility in hexamethyldisilazane treated Pentacene bottom contact devices

The effect of substrate temperature and deposition rate on the film morphology, crystallinity, and electronic properties of Pentacene transistors treated with hexamethyldisilazane (HMDS) is studied. The gate bias dependence of mobility is used to estimate the width of the density of states and thereby quantify the disorder of the highest occupied molecular orbital. A low deposition rate and the substrate held at room temperature are shown to be the optimal conditions for good mobility (0.20 cm2 V−1 s−1) and low electronic disorder (50 ± 10 meV). X-ray diffraction measurements are performed to quantify the ratio of the two crystalline phases (thin-film phase and bulk phase) present in the film. The crystalline phases, rather than grain size, plays a significant role in determining the charge carrier mobility. Film deposition with the substrate at room temperature leads to low electronic disorder as the film is composed of one crystalline phase (thin-film phase), while high substrate temperature makes the film increasingly polymorphic, leading to increased electronic disorder (up to 230 meV). A high deposition rate leads to poor morphology of Pentacene near the source/drain electrode edge, thereby leading to increased contact resistance and electronic disorder. Hence, a low growth rate at room temperature is required for HMDS treated substrates to induce good crystalline properties of the film in the channel region, which results in enhanced electronic properties of the transistors.

Effect of Thermal Annealing on the Charge Carrier Selectivity of Ultra‐Thin Organic Interface Dipoles in Silicon Organic Heterojunction Solar Cells

Interfacial layers consisting of organic molecules with a permanent dipole moment exhibit enhanced charge carrier selectivity when applied as electron‐selective contacts in crystalline silicon (c‐Si) heterojunction solar cells. It is found that thermal annealing has a detrimental effect on the charge carrier selectivity of dipole materials based on the amino acid l‐histidine mixed with a fluorosurfactant. Although, the implied open‐circuit voltage (iVoc) increases with annealing, the Voc decreases significantly which is accompanied by a decrease in the built‐in voltage (Vbi) and increase in the specific contact resistivity (ρc). Based on numerical device simulations, it is concluded that the tunneling of electrons through the dipole layer becomes less effective with increasing annealing temperature due to the decomposition of the dipole materials. The decomposition leads to a more “resistive” interfacial layer and to a gradient in the electron quasi‐Fermi potential and, thus, a decrease in Voc. Furthermore, storage under ambient air at room temperature degraded the electron‐selective contacts substantially, limiting the potential of the dipole material for the application in silicon organic heterojunction solar cells.