Electrical Contact Properties Research Articles

Al concentration-dependent electrical modulation of Al-doped ZnO thin film using atomic layer deposition

A series of 150-nm-thick Al-doped ZnO (AZO) thin films with various Al doping concentrations were deposited by atomic layer deposition technique to determine their applicability in transparent electronic devices. For incorporation into transparent electrodes, the electrical properties of AZO films must be modulated to minimize the parasitic effect. The results show that AZO thin films with various Al dopant concentrations had different work-functions and electrical contact properties, while the other physical characteristics were not significantly changed. Hence, AZO thin films can be used as transparent conducting oxide materials and are potential alternatives for the currently used indium-tin-oxide (ITO) thin films.

P‐225: Late‐News Poster: Improving Specific Contact Resistivity of a‐IGZO Thin‐Film‐Transistors via Multi‐stack Interlayer

We report the effects of sputter‐based multi‐stack interlayer on the electrical contact properties of a‐IGZO TFTs. The a‐IGZO TFTs with a multi‐stack interlayer of TiN and IGTO showed remarkable outcomes, including the lowest specific contact resistivity (ρC) and the highest field‐effect mobility (μFET). This research suggests a highly effective approach to reduce the contact resistivity of oxide semiconductors by nearly two orders magnitude.

First-Principles and Experimental Study of Ge, V, Ta-Doped AgNi Electrical Contact Materials

To explore the stability, electrical, and mechanical characteristics of undoped AgNi alongside AgNi doped with elemental Ge, V, and Ta, we performed calculations on their electronic structures using density functional theory from first-principles. We also prepared AgNi(17) and AgNi-x(Ge, V, Ta) electrical contact materials using the powder metallurgy technique, and they were subsequently assessed experimentally. The electrical properties of these materials were evaluated under a 24 V/15 A DC-resistive load using the JF04D contact material testing system. A three-dimensional morphology scanner was employed to examine the contact surface and investigate the erosion patterns of the materials. Our findings indicate that doping with metal elements significantly enhanced the mechanical properties of electrical contacts, including conductivity and hardness, and optimizes arc parameters while improving resistance to arc erosion. Notably, AgNi-Ge demonstrated superior conductivity and arc erosion resistance, showing significant improvements over the undoped AgNi contacts. This research provides a theoretical foundation for selecting doping elements aimed at enhancing the performance of AgNi electrical contact materials.

Specific contact resistivity reduction in amorphous IGZO thin-film transistors through a TiN/IGTO heterogeneous interlayer

Oxide semiconductors have gained significant attention in electronic device industry due to their high potential for emerging thin-film transistor (TFT) applications. However, electrical contact properties such as specific contact resistivity (ρC) and width-normalized contact resistance (RCW) are significantly inferior in oxide TFTs compared to conventional silicon metal oxide semiconductor field-effect transistors. In this study, a multi-stack interlayer (IL) consisting of titanium nitride (TiN) and indium-gallium-tin-oxide (IGTO) is inserted between source/drain electrodes and amorphous indium-gallium-zinc-oxide (IGZO). The TiN is introduced to increase conductivity of the underlying layer, while IGTO acts as an n+-layer. Our findings reveal IGTO thickness (tIGTO)-dependent electrical contact properties of IGZO TFT, where ρC and RCW decrease as tIGTO increases to 8 nm. However, at tIGTO > 8 nm, they increase mainly due to IGTO crystallization-induced contact interface aggravation. Consequently, the IGZO TFTs with a TiN/IGTO (3/8 nm) IL reveal the lowest ρC and RCW of 9.0 × 10−6 Ω·cm2 and 0.7 Ω·cm, significantly lower than 8.0 × 10−4 Ω·cm2 and 6.9 Ω·cm in the TFTs without the IL, respectively. This improved electrical contact properties increases field-effect mobility from 39.9 to 45.0 cm2/Vs. This study demonstrates the effectiveness of this multi-stack IL approach in oxide TFTs.

Arc erosion resistance of Al2O3–Cu/35Mo composites reinforced by trace graphene oxide

In this study, Al2O3–Cu/35Mo composites were prepared by rapid hot-press sintering-internal oxidation method, and the materials were modified by adding trace amounts of graphene oxide (GO). The results show that the relative densities of the composites are above 99%, the γ-Al2O3 generated by internal oxidation is diffusely distributed on the copper matrix. The incorporation of GO produced a small number of hard MoC particles at the interface, which facilitated the interfacial bonding of the composites. In the 30 V DC, 10–30 A electrical contact test, the anode mass of the composites increases, while the cathode mass decreases. And GO reduces the total mass loss of the electric contact by 63.6%, 38.9%, 51.3% and 20.9%, respectively. A comparison of the electrical contact properties of the two materials showed that the addition of GO dispersed the concentrated erosion of the arc. At 10 A and 30 A, the arc energy is reduced by 75.5% and 12.5%, respectively. With the gradual increase in electric current, GO makes the Al2O3–Cu/35Mo composites more stable during the electric contact process, improves the anti-welding ability of the contact and reduces contact resistance.

Prediction of contact resistance of electrical contact wear using different machine learning algorithms

H62 brass material is one of the important materials in the process of electrical energy transmission and signal transmission, and has excellent performance in all aspects. Since the wear behavior of electrical contact pairs is particularly complex when they are in service, we evaluated the effects of load, sliding velocity, displacement amplitude, current intensity, and surface roughness on the changes in contact resistance. Machine learning (ML) algorithms were used to predict the electrical contact performance of different factors after wear to determine the correlation between different factors and contact resistance. Random forest (RF), support vector regression (SVR) and BP neural network (BPNN) algorithms were used to establish RF, SVR and BPNN models, respectively, and the experimental data were trained and tested. It was proved that BP neural network model could better predict the stable mean resistance of H62 brass alloy after wear. Characteristic analysis shows that the load and current have great influence on the predicted electrical contact properties. The wear behavior of electrical contacts is influenced by factors such as load, sliding speed, displacement amplitude, current intensity, and surface roughness during operation. Machine learning algorithms can predict the electrical contact performance after wear caused by these factors. Experimental results indicate that an increase in load, current, and surface roughness leads to a decrease in stable mean resistance, while an increase in displacement amplitude and frequency results in an increase in stable mean resistance, leading to a decline in electrical contact performance. To reduce testing time and costs and quickly obtain the electrical contact performance of H62 brass alloy after wear caused by different factors, three algorithms (random forest (RF), support vector regression (SVR), and BP neural network (BPNN)) were used to train and test experimental results, resulting in a machine learning model suitable for predicting the stable mean resistance of H62 brass alloy after wear. The prediction results showed that the BPNN model performed better in predicting the electrical contact performance compared to the RF and SVR models.

How to Accurately Determine the Ohmic Contact Properties on n-Type 4H-SiC

The electrical properties of ohmic contacts are classically investigated by using the transfer length method (TLM). In the literature, the TLM patterns are fabricated onto different substrate configurations, especially directly onto the 4H-SiC wafers. But, due to the high doping level of commercial substrates, the current is not confined close to the contact and, in this case, the specific contact resistance (SCR) value is overestimated. In this article, we propose, by the means of simulations, to investigate the influence of the layer under the contact towards the estimation of the SCR. The simulation results highlight that, for an accurate determination of the SCR values, an isolation layer between the contact and the silicon carbide substrate is mandatory. Thus, we have determined the characteristics (doping level and thickness) of a suitable isolation layer compatible with SCR values ranging from 10−3 to 10−6 Ω·cm2.

Electrical contact properties of 2D metal-semiconductor heterojunctions composed of different phases of NbS<sub>2</sub> and GeS<sub>2</sub>

Metal-semiconductor heterojunction (MSJ) is the basis for developing novel devices. Here, we consider different two-dimensional van der Waals MSJs consisting of different-phase metals H- and T-NbS<sub>2</sub> and semiconductor GeS<sub>2</sub>, and conduct an in-depth study of their structural stabilities, electronic and electrical contact properties, with an emphasis on exploring the dependence of the electrical contact properties of the MSJs on the different phases of metals. Calculation results of their binding energy, phonon spectra, AIMD simulations, and mechanical properties show that both heterojunctions are highly stable, which implies that it is possible to prepare them experimentally and feasible to use them for designing electronic devices. The intrinsic H-NbS<sub>2</sub>/GeS<sub>2</sub> and T-NbS<sub>2</sub>/GeS<sub>2</sub> heterojunctions form p-type Schottky contacts and quasi-n-type Ohmic contacts, respectively. It is also found that their Schottky barrier heights (SBHs) and electrical contact types can be effectively modulated by an applied electric field and biaxial strain. For example, for the H-NbS<sub>2</sub>/GeS<sub>2</sub> heterojunction, Ohmic contact can be achieved regardless of applying a positive/negative electric field or planar biaxial compression, while for the T-NbS<sub>2</sub>/GeS<sub>2</sub> heterojunction, Ohmic contact can be achieved only at a very low negative electric field. The planar biaxial stretching can achieve quasi-Ohmic contact. In other words, when the semiconductor GeS<sub>2</sub> monolayer is used as the channel material of the field effect transistor and contacts different metal NbS<sub>2</sub> monolayers to form the MSJ, the interfacial Schottky barriers are distinctly different, and each of them has its own advantages in different situations (intrinsic or physically regulated). Therefore, this study is of great significance for understanding the physical mechanism of the electrical contact behaviors for H(T)-NbS<sub>2</sub>/GeS<sub>2</sub> heterojunction, especially for providing the theoretical reference for selecting suitable metal electrodes for the development of high-performance electronic devices.

Key role of initial interface on contact characteristics of Pd/p-GaN

Sequential three-layers of Pd/Pt/Au were deposited on p-GaN by magnetron sputtering under high vacuum (HV, ∼1.33 × 10−4 Pa) and ultra-high vacuum (UHV, ∼1.33 × 10−7 Pa) background conditions, respectively, for investigating the electrical contact properties. Linear I–V curves are observed in the samples deposited under the UHV conditions, whereas nonlinear I–V characteristics are obtained in the samples deposited under the HV vacuum. The depth profiles of X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS) of the as-deposited samples were probed in detail. It is found that the amounts of O and OH as well as Pd oxide of the sample deposited under the HV background condition are larger than those of the sample deposited under the UHV conditions due to the higher residual gases such as water in the HV chamber. The oxide layer leads to an extra barrier, influencing the electrical characteristics of Pd/Pt/Au/p-GaN contact. This study demonstrates that metal deposition under the UHV environmental conditions can reduce and even prevent formation of oxide on p-GaN surface, and hence favor making a good ohmic contact on p-GaN.

Break-Arc Erosion and Material Transfer Behavior of Pt–Ir and Pt–Ir–Y Electrical Contact Materials under Different Currents

In order to explore the influence of rare earth element Y on the electrical contact properties of Pt–Ir alloys, Pt–10Ir–Y and Pt–25Ir–Y were prepared via arc melting combined with thermal processing, and electrical contact experiments were carried out with a DC voltage of 24 V and current ranging from 5 A to 25 A. Comparative analyses were conducted to analyze the changes in the break arc duration and arc energy, as well as the contact resistance before and after the addition of Y. The arc erosion surface morphology was characterized, and the transfer behavior of the alloys was discussed. The results show that at 5 A and 25 A, adding Y improves the stability of the arc duration of the Pt–Ir alloy, but it increases the overall arcing energy and decreases the stability. The contact resistance of the Pt–Ir alloy shows a clear partitioning phenomenon; the partitioning phenomenon disappears after the addition of Y, and the contact resistance fluctuates around the average value. The material transfer direction of the Pt–Ir alloy is affected by the current change, while the material transfer direction of the Pt–Ir–Y alloy is always from cathode to anode. The research results provide a reference for the performance optimization of Pt–Ir alloys.

Fluid Flow in the Gas Diffusion Layer Using Computational Fluid Dynamics and Microscopy Techniques

The utilization of a proton exchange membrane fuel cell (PEMFC) as an energy provider using hydrogen as a fuel has increased drastically. The reasons are the current limitation of fossil fuel-based devices, pollutants-free, high efficiency, and zero-carbon emission. The life-cycle assessment results of this type of fuel cell have also indicated the lowest contribution to global warming, human health, and resource scarcity in comparison to other types of fuel cells. In this regard, improving the performance of PEMFC is of importance.As an important component of the PEMFC, the gas diffusion layer (GDL) transports the gas reactants to the catalyst layer with the least electrical resistance. The GDL is often made of carbon fibers and should have a surface with good electrical contact and hydrophobic properties to facilitate the water removal. Remaining water in the GDL will result in difficulties during the cold-start and enhances the degradation of this layer. It is believed that the water removal of the GDL has a direct relationship with the capillary pressure, which is strongly linked to the GDL’s microstructure and wettability. However, further investigations can be done once a comprehensive simulation model is developed to monitor the changes in the GDL liquid removal by the effective parameters.In this regard, the Focused Ion Beam-Scanning Electron Microscopy (FIB-SEM) has been used to perform three-dimensional cross-section imaging of the GDL. The GDL samples are provided by Freudenberg in which the Microporous layer (MPL) is impregnated into the GDL. The average porosity of this sample is in the range of 75% while having the in-plane gas permeability of 2.4 under a compressive stress of 1 MPa. The utilized resin for FIB-SEM imaging is a mixture of Epoxy embedding medium (diglycidyl ether of bisphenol – A) with two different hardeners DDSA (2-Dodecenylsuccinic anhydride) and MNA (Methylnadic anhydride), which will be mixed with DPM – 30 [2,4,6 – Tris(dimethylaminomethyl)phenol] as the accelerator, all provided by Sigma Aldrich. After the preparation of the resin, 0.4 gr of Cobalt (II) acetylacetonate nanoparticles (supported by Sigma Aldrich) were added to 7.14 ml of the resin to improve the contrast of the images. The samples were impregnated with the resin under vacuum to be pressurized (3 MPa) for 20 minutes, and afterward, heated in an oven at 60℃ for 12 hours. The surfaces for analyses were cut by a diamond wire, polished by abrasive plates down to 0.1 and gold coated (20nm).FIB-SEM acquisition consisted of the polishing of cross-sections with a focused ion beam (LMIS Ga+ source) at 30 keV and 1 nA (Zeiss Crossbeam 540), followed by imaging with an electron beam at acceleration voltages of 1.0, 3.0 kV. Milling and imaging were performed at a working distance of 5.2 mm and stage tilt of 54°, i.e., the coincidence point of the electron and ion beams.Once the three-dimensional cross-sections of the GDL are obtained, the segmentation and reconstruction will be made to provide the needed geometry for fluid flow simulation and to calculate the microstructural properties. Fig. 1 shows the generated structure of the GDL after the segmentation and reconstruction of the cross-section images. The geometry will be then used to characterize the effective parameters of the thermal/water management of the PEMFC. This study can also be a valid reference for future computational fluid dynamic analyses in the GDL using the numerical modeling with the conservative equations or the Lattice Boltzmann modeling (LBM) with the kinetic and particle distribution equations. Keywords : Proton exchange membrane fuel cell (PEMFC); Gas Diffusion Layer (GDL); Focused Ion Beam- Scanning Electron Microscopy (FIB-SEM); Three-dimensional simulation; Lattice Boltzmann method (LBM) Figure 1

Improved electrical contact property of Si-doped GaN thin films deposited by PEALD with various growth cycle ratio of SiNx and GaN

Gallium Nitride (GaN) is becoming increasingly attractive due to its advantages in efficiency, switching speed, and high temperature operation. Although the performance of GaN in light-emitting devices and power electronics has been significantly improved, the need to reduce the power loss of GaN-based devices still exists. In this paper, Si derived from the SiNx sub-cycle in plasma-enhanced atomic layer deposition (PEALD) was used as a dopant to improve the ohmic contact resistance of GaN. The doping concentration of Si ranging from 0% to 33 at% were obtained by varying the SiNx sub-cycle ratio from 0% to 50%. A 13.56 at% Si-doped GaN film with moderate SiN bonding deposited at a SiNx sub-cycle ratio of 20% exhibits the highest carrier concentration of 1.29 × 1018 cm−3 and the lowest resistivity of 0.78 Ω·cm. The transmission line model (TLM) measurements show that the as-deposited Si-doped GaN has a specific contact resistance of 4.77 × 101 Ω·cm2, which decreases to 8.15 × 10−4 Ω·cm2 after annealing at 500 °C.

Enhancement mechanism of carbon fiber on the current-carrying tribological properties of Cf-Al2O3/Cu composites

Cf-Al2O3/Cu composites were fabricated by powder metallurgy combined with internal oxidation. The microstructure, electrical contact properties and tribological properties of the fabricated composites were characterized. The results showed that the addition of an appropriate amount of carbon fibers improved the tribological properties of Al2O3/Cu composites. The friction coefficient of the composites is lower (0.182) and the specific wear rate decreased by 64.2% in comparison with Al2O3/Cu composites. The reduction of arc erosion reduced the roughness of the friction surface of the composite and improved the stability of the friction system. And the improvement of friction stability, in turn, avoided the formation of bumps and pits on the friction surface and prevented concentrated arc erosion at the bumps.

NbS2/MoSi2P4 van der Waals Heterojunction: Flexibly tunable electrical contact properties and potential applications for Schottky junction devices

To obtain miniaturized and high-performance nanoelectronic devices, it is still crucially technical problem to realize ohmic contact at metal–semiconductor interface. Here, we construct H-, T-NbS2/MoSi2P4 van der Waals heterojunctions (vdWHs) and theoretically explore their mechanic and electronic behaviors, focusing on electrical contact features and tunability as well as Schottky junction device properties. The suitable Poisson’s ratio and sufficient rigidity suggest that such vdWHs are highly favorable to act as electrode or channel materials. The quasi-ohmic contact for H-NbS2/MSP occurs in the intrinsic equilibrium state (ES), and its entire ohmic contact emerges only by a very small interlayer spacing compression. For both H- and T-NbS2/MSP, entire ohmic contacts can be realized by applied appropriate electric field. Based on these studies, we design 5 nm gate-controlled Schottky junction devices. The calculated energy-resolved currents show that the thermal emission transmission plays an important role in rectification, making the rectification ratio exceeding 105, enhanced further by positive gate voltage applied. These behaviors can be identified by the calculated PLDOS, which shows that the highly asymmetric device potential barrier with respect to bias polarity and tuned flexibly by gate voltage results in a highly asymmetric electron transport under different directional biases. Our study provide a new possibility for designing high-performance Schottky junction devices.

Silicon heterojunction solar cells with up to 26.81% efficiency achieved by electrically optimized nanocrystalline-silicon hole contact layers

Silicon heterojunction (SHJ) solar cells have reached high power conversion efficiency owing to their effective passivating contact structures. Improvements in the optoelectronic properties of these contacts can enable higher device efficiency, thus further consolidating the commercial potential of SHJ technology. Here we increase the efficiency of back junction SHJ solar cells with improved back contacts consisting of p-type doped nanocrystalline silicon and a transparent conductive oxide with a low sheet resistance. The electrical properties of the hole-selective contact are analysed and compared with a p-type doped amorphous silicon contact. We demonstrate improvement in the charge carrier transport and a low contact resistivity (<5 mΩ cm2). Eventually, we report a series of certified power conversion efficiencies of up to 26.81% and fill factors up to 86.59% on industry-grade silicon wafers (274 cm2, M6 size).

Effect of short-time hot repressing on a Ag-SnO2 contact material containing CuO additive

It remains difficult to achieve high-density metal matrix composites by traditional powder metallurgy. In this study, short-time hot repressing was proposed to densify a Ag-SnO2 contact material prepared by powder metallurgy. The effect of the vacuum repressing temperature on the Ag-SnO2 material containing CuO additive was systematically investigated under a constant pressure of 200 MPa. The results showed that the relative density of the material repressed at 800 °C for 10 min can be increased to as high as 99.75%. The microstructure of the Ag-SnO2(CuO) material was obviously refined and homogenized by short-time hot repressing. The dispersive distribution of the SnO2 particles in the Ag matrix was induced, resulting in the elimination of particle aggregation. It is worth noting that almost all the CuO additive was decomposed into Cu2O after hot repressing, which was beneficial for improving the electrical contact properties. Furthermore, the arc energy of the repressed material significantly decreased with increasing repressing temperature, which can be attributed to the high density and uniform microstructure. During arc erosion, the mass loss of the Ag-SnO2(CuO) materials repressed at 800 °C was smallest, and the formation of pores and cracks was inhibited. However, the relative density of the material showed a tendency to decrease when the repressing temperature reached 850 °C.

Semimetal contacts to monolayer semiconductor: weak metalization as an effective mechanism to Schottky barrier lowering

Recent experiment has uncovered semimetal bismuth (Bi) as an excellent electrical contact to monolayer MoS2 with ultralow contact resistance. The contact physics of the broader semimetal/monolayer-semiconductor family beyond Bi/MoS2, however, remains largely unexplored thus far. Here we perform a comprehensive first-principle density functional theory investigation on the electrical contact properties between six archetypal two-dimensional (2D) transition metal dichalcogenide (TMDC) semiconductors, i.e. MoS2, WS2, MoSe2, WSe2, MoTe2 and WTe2, and two representative types of semimetals, Bi and antimony (Sb). As Bi and Sb work functions energetically aligns well with the TMDC conduction band edge, Ohmic or nearly-Ohmic n-type contacts are prevalent. The interlayer distance of semimetal/TMDC contacts are significantly larger than that of the metal/TMDC counterparts, which results in only weak metalization of TMDC upon contact formation. Intriguingly, such weak metalization generates semimetal-induced gap states (SMIGSs) that extends below the conduction band minimum, thus offering an effective mechanism to reduce or eliminate the n-type Schottky barrier height (SBH) while still preserving the electronic structures of 2D TMDC. A modified Schottky–Mott rule that takes into account SMIGS, interface dipole potential, and Fermi level shifting is proposed, which provides an improved agreement with the density functional theory-simulated SBH. We further show that the tunneling-specific resistivity of Sb/TMDC contacts are generally lower than the Bi counterparts, thus indicating a better charge injection efficiency can be achieved through Sb contacts. Our findings reveal the promising potential of Bi and Sb as excellent companion electrode materials for advancing 2D semiconductor device technology.

Progress, Challenges, and Opportunities in Oxide Semiconductor Devices: A Key Building Block for Applications Ranging from Display Backplanes to 3D Integrated Semiconductor Chips.

As Si has faced physical limits on further scaling down, novel semiconducting materials such as 2D transition metal dichalcogenides and oxide semiconductors (OSs) have gained tremendous attention to continue the ever-demanding downscaling represented by Moore's law. Among them, OS is considered to be the most promising alternative material because it has intriguing features such as modest mobility, extremely low off-current, great uniformity, and low-temperature processibility with conventional complementary-metal-oxide-semiconductor-compatible methods. In practice, OS has successfully replaced hydrogenated amorphous Si in high-end liquid crystal display devices and has now become a standard backplane electronic for organic light-emitting diode displays despite the short time since their invention in 2004. For OS to be implemented in next-generation electronics such as back-end-of-line transistor applications in monolithic 3D integration beyond the display applications, however, there is still much room for further study, such as high mobility, immune short-channel effects, low electrical contact properties, etc. This study reviews the brief history of OS and recent progress in device applications from a material science and device physics point of view. Simultaneously, remaining challenges and opportunities in OS for use in next-generation electronics are discussed.

Role of Ti and W in the Ni-based ohmic contacts to n-type 4H-SiC

The paper investigated the influence mechanism of Ti and W on the electrical and structural properties of the Ni-based ohmic contacts to n-type 4H-SiC. The variation of specific contact resistances (SCRs) with different contact structures was found to be correlated to the relative proportion of the total contact area occupied by the (220) plane than that of the (301) plane at the contact interface for the polycrystalline and textured δ-Ni2Si films characterized by the X-ray diffraction (XRD). Due to the formation of metal carbides, the W layer was found to be beneficial for a higher relative proportion contributing to a reduction of SCR. In contrast, the Ti layer was detrimental owing to the incorporation of metal oxides and carbides. Therefore, W is considered a better candidate to improve the thermal stability of Ni-based ohmic contacts to n-type 4H-SiC while maintaining a low specific contact resistance. Moreover, it was found that the free carbon atoms were immobilized or blocked by the W or Ti layer, and a greater distance of free carbon away from the contact surface led to a smoother and more uniform surface morphology. We believe that this discovery provides a valuable insight into the tuning of surface morphology for the wire bonding challenge.

Electrical Contact Properties of Nanostructured Carbon Films under Transverse Current-carrying Condition

Electrical Contact Properties of Nanostructured Carbon Films under Transverse Current-carrying Condition