Contact Resistance Characteristics Research Articles

Low-voltage organic field-effect transistors by using solution-processable high-κ inorganic-polymer hybrid dielectrics

Organic field-effect transistors (OFETs) incorporating hybrid high-κ inorganic Al2O3 and polymer dielectrics, including polyvinyl alcohol (PVA), polystyrene (PS), or polymethyl methacrylate (PMMA), through solution-processing techniques were fabricated. The analyses revealed that the high surface energy and hydrophilicity property of Al2O3 and PVA, and the relatively hydrophobic property of PS surface, hindered the performance of corresponding OFETs. The Al2O3/PMMA-based OFET achieved the optimized performance, with a threshold voltage of −2.7 V, a hole carrier mobility of 0.056 cm2/Vs, and a current on/off ratio of 1.0 × 104 at a low operating voltage of −5 V. Through analyzing the characteristics of leakage current, capacitance, contact resistance, and trap density of OFETs, we found that the PMMA-engaged films possessed the optimized electrical properties. The introduction of PMMA eliminated the interfacial trapping, thereby lowering the threshold voltage and enhancing the performance of the device. The COMSOL Multiphysics simulation was conducted to confirm the physical mechanism. The strategy of utilizing Al2O3/PMMA hybrid dielectric could simultaneously ensure the low operating voltage and good performance of OFET, while guaranteeing the low leakage current by the thick PMMA.

Contact Resistance and Over-Current Characteristics of No-Insulation High-Temperature Superconducting Coils Impregnated With an Electrically-Conductive Epoxy

Contact Resistance and Over-Current Characteristics of No-Insulation High-Temperature Superconducting Coils Impregnated With an Electrically-Conductive Epoxy

Optimization of Contact Resistance and DC Characteristics for AlGaN/GaN HEMTs Utilizing Sub-10 nm Nanohole Etching

In this paper, the contact resistance of AlGaN/GaN high electron mobility transistor (HEMT) was improved by introducing nanoscale hole arrays in ohmic regions, and the DC characteristics of the conventional structure and nanohole etching structure for HEMTs were measured for comparison. Sub-10 nm nanoholes were patterned on the ohmic area surface of AlGaN using electron beam lithography and a low-temperature short-time development. Various dwell times of e-beam exposure from 5 to 30 μs were investigated and the corresponding contact resistance of the nano hole etching structure and planar structure were compared by the transmission line model (TLM) method. We observed a reduced contact resistance from 1.82 to 0.47 Ω-mm by performing a dwell time of 5 μs of exposure for nanohole formation compared to the conventional structure. Furthermore, the DC characteristics demonstrate that the maximum drain current for HEMTs was enhanced from 319 to 496 mA/mm by utilizing this optimized ohmic contact. These results show that devices with sub-10 nm nanohole ohmic contacts exhibit an improved contact resistance over the conventional structure, optimizing device performance for HEMTs, including a lower on-resistance and higher maximum drain current.

CURRENT LEADS FOR RESISTIVE CCCM HEATERS

The article justifies the necessity of taking into account the transient electrical resistance of the welding contact between the titanium current lead and the resistive element of the heater made of carbon-carbon composite material (CCCM) during its manufacturing.
 Carbon-carbon composite material possesses a unique set of technical characteristics that make it suitable as a structural material for manufacturing resistive heaters operating in the temperature range from 400°C to 2500°C in a vacuum or protective atmosphere. The use of CCCM heaters in the thermal chambers of electrothermal engines to convert electrical energy into thermal energy allows them to be employed for temperature measurement inside the engine's thermal chamber. The utilization of an integrated temperature assessment of the CCCM heater, which relies on the resistance change of the heater with increasing temperature and essentially involves measuring the electrical current passing through the heater, requires ensuring accurate values of both the electrical resistance of the heater itself and the electrical resistance at the point of contact with the current lead.
 The design of the heater has a particular feature, which is the need to supply electrical current to two lamellas of the resistive element of the CCCM heater, located on one side of the heater. For welding the joints between the titanium wire and the resistive element of the heater, TIG welding with a surface arc in an argon environment was applied, with argon being supplied between the welding point and the non-consumable tungsten electrode.
 Laboratory tests revealed that detachable connections of the titanium wire to the resistive element of the CCCM heater and separable connections (such as bolts, screws, and wedges) cannot meet the requirements for contact resistance stability for various reasons. Among non-detachable connections, only welded joints demonstrated stable electrical contact resistance characteristics.
 The electrical resistance of the heater with current leads should be 3.8±0.2 Ohms. The tolerance value for resistance is determined by several factors, including the physical properties of CCCM, the technology of mechanical processing, the method of applying protective coatings, the resistance of the welding joint, and others.
 During mechanical tests of the welding joint between the titanium wire and the heater, it was observed that the wire detachment from the heater occurs with residues of CCCM and a transitional layer of titanium carbide, which forms during welding and can contribute to additional electrical resistance of the heater. Thermal deformation of the CCCM heater in the welding zone does not occur.
 The results of the conducted research demonstrate that the installation of titanium current leads by welding increases the resistance value of the resistive element of the CCCM heater due to the chemical reaction between the titanium alloy and the resistive element, leading to the formation of an additional layer of titanium carbide. Therefore, the electrical resistance of the resistive element of the CCCM heater during its manufacturing, before welding two titanium wires for current leads, should be reduced, taking into account the transitional electrical resistance of the two welding contacts.

Contact reliability design modeling for wire spring-hole electrical connectors

Wire spring-hole connectors are widely used in the aerospace system in recent years due to their characteristics of low contact resistance and small insertion force. Contact failure is the main failure mode of wire spring-hole electrical connectors. By analyzing the contact failure mechanism of wire spring-hole electrical connectors, it is clear that the leading causes of contact failure are the growth of the oxide film layer on the surface of the contact and the stress relaxation of the wire spring. Based on the reaction kinetics and tunneling theory, the evolution of the tunneling resistivity of the oxide film layer on the surface is described. The rule of contact stress is revealed by establishing a mechanical model of wire spring. Furthermore, combing with the physical equation of accelerated failure of contact resistance, a contact reliability design model with design parameters is established. Finally, the model is verified by utilizing the accelerated test data of a type of wire spring-hole electrical connector. This model provides a theoretical basis for the reliability evaluation and design of wire spring-hole electrical connectors in the long-term storage environment.

Contact Resistance and Current Characteristics of NI HTS Coils in Low Frequency AC Method

The development of high-performance HTS magnets requires a method to correctly measure the contact resistance between turns of no-insulation (NI) coils. We have proposed a method to measure the turn-to-turn contact resistance of NI coils using low frequency alternating current (LFAC). In the LFAC method, AC current is used, and it is assumed that all the AC current flows in the radial direction of the NI HTS coil. To confirm the reliability of the proposed measurement method, AC current distribution characteristics were evaluated using four (quarter circle, 1/4 size) pickup coils in a previous study. The pickup coils were mounted under the NI test coils and the current bypass characteristics from circumferential to radial direction were evaluated as a function of frequency. However, the size of the fabricated four pickup coils was relatively large compared to the test coil, so its sensitivity and spatial resolution were not sufficient. Therefore, in this study, we prepared eight pickup coils smaller than the 1/4 size pickup coil used in the previous study. Two test coils with winding tensions of 0.5 and 1 kg were prepared, and the non-uniformity of the contact resistance of both NI coils was detected using eight pickup coils. We also identified locations in the test coil where the contact resistance changed due to multiple cooling cycles by liquid nitrogen.

Pure edge-contact devices on single-layer-CVD-graphene integrated into a single chip

We present a simple and cost-effective fabrication technique for on-chip integration of pure edge contact two-terminal (2T) and Graphene field effect transistor (GFET) devices with low contact resistance and nonlinear characteristics based on single-layer chemical-vapor-deposited (CVD) graphene. We use a smart print-based mask projection technique with a 10X magnification objective lens for maskless lithography followed by thermal evaporation of the contact material Cr-Pd-Au through three different angles (90° and ± 45°) using a customized inclined-angle sample-holder to control the angle during normal incidence evaporation for edge-contact to graphene. Our fabrication technique, graphene quality, and contact geometry enable pure metal contact to 2D single-layer graphene allowing electron transport through the 1D atomic edge of graphene. Our devices show some signatures of edge contact to graphene in terms of very low contact resistance of 23.5 Ω, the sheet resistance of 11.5 Ω, and sharp nonlinear voltage-current characteristics (VCC) which are highly sensitive to the bias voltage. This study may find application in future graphene-integrated chip-scale passive or active low-power electronic devices.

Thermal Field Simulation and Analysis of Tulip Contact Based on Virtual Material Method

In order to analyze the temperature distribution of circuit breaker tulip contact, a thermal field simulation model for tulip contact is built combined with the electromagnetic-stress-thermal coupled finite element simulation and virtual material method which models the contact resistance characteristics of tulip contact. The temperature rise characteristic of tulip contacts under rated current conditions and short-circuit conditions is analyzed with the model. Results show that the virtual material method can describe the contraction resistance and additional resistance at the end of the contact finger simultaneously, so as to simulate the partial high temperature of the contact interface. Then, the influence of spring pressure and pressure uniformity on the thermal field of tulip contact is analyzed. Results show that the decrease of spring pressure and the imbalance of contact finger pressure may lead to an increase in the temperature rise of the tulip contact. The proposed method can be used as a reference for the design and the overheating analysis of tulip contact.

Mathematical Model of Contact Resistance in Pantograph-Catenary System Considering Rough Surface Characteristics

Pantograph-catenary system is a key component of high-speed railway. Under high speed and strong current operation conditions, the surface roughness of the sliding electrical contact between contact wire and slide changes continuously. It will cause the fluctuation of contact resistance and lower the electrical contact property of the system. Therefore, it is of great significance to study the relationships between the contact resistance and surface roughness characteristics. In this article, lots of current-carrying friction experiments were carried out under different contact pressure, contact current, and sliding speed conditions. A roughness tester was used to measure the roughness of the contact surface after the experiment. Four characteristic parameters were proposed to describe the roughness. They are the root mean square and the maximum peak height of the rough surface, the peak count, and the curvature radius of asperity, respectively. The function relationships between these characteristic parameters and experimental conditions were obtained and discussed. On the basis of Greenwood–Williamson contact model, a new mathematical model of contact resistance in the pantograph-catenary system considering rough surface characteristics was established and verified. It can be used to further study the current conduction mechanism of sliding electrical contact in pantograph-catenary system and evaluate the electrical contact performance.

Bondability of ultrasonic Aluminum bonds on the molybdenum (de)selenide and molybdenum of back contact layer of copper indium gallium (de)selenide CIGS thin film photovoltaic solar panel

This paper aims to study the bondability of ultrasonic Aluminum, Al bonds on Mo and MoSe2 layers of back-contact metal of copper indium gallium (de)selenide (CIGS) thin film photovoltaic (TFPV) solar panel. The bondability of ultrasonic Al bonds were evaluated based on the contact resistance, Rc, peel strength and electrical characteristics measured using transmission line method (TLM), peel test, and current–voltage (I-V) measurement, respectively. Besides, the qualitative results of load-distance profiles from tensile test also have been used to evaluate the bondability of the ultrasonic Al bonds. Two type of lamination constructions namely construction 1 and construction 2 were built on the CIGS TPFV solar panel with ultrasonic Al bonds on Mo and MoSe2. It was noted that the new method of removing CIGS layer up until MoSe2 is the plausible technique to be used. Ultrasonic Al bond on Mo layer has higher bondability as compared to that of ultrasonic Al bond on MoSe2 through the quantitative results of Rc, peel strength and qualitative result of load-distance profile. CIGS TFPV solar panel with construction 2 is the suitable construction for the CIGS TFPV solar panel due to the higher rigidity, and even stress distribution experienced during lamination process as compared to that of construction 1. It is noted that steps taken from ultrasonic bonding until lamination process has increased the cumulative contact area and decreased the Rc and consequently increased the efficiency of CIGS TFPV solar panel with ultrasonic Al bond on MoSe2 layer.

Effects of the Synthesis Coating Parameters for Metal Bipolar Plates

Metallic bipolar plates tendency to have high contact resistance, but also very susceptible to corrosion. This may decrease in the performance of fuel cells after several times of usage in fuel cell applications. Research has shown that after a metal plate was coated, the characteristic of materials dependent on the type, composition of the coating materials and the method. This study determines design of coating parameters including gas flow rate, DC power, and deposition time of coating for metal bipolar plates, which can be an indicator of the suitability of these plates for use as bipolar plates in proton exchange membrane fuel cell (PEMFC) applications. The aim of this research was to obtain a limitation range value of parameters that can be used as a standard for the use of metal plates as bipolar plates. The optimization parameters designed by Taguchi are used to determine the characteristics of interfacial contact resistance (ICR) and corrosion current density (Icorr). The integration of the Taguchi method with simulation can show the optimal design parameters of the coating on the various materials use. The optimization feature based on Taguchi is applied to ICR and Icorr values, to determine the feasibility of metal plates as potential bipolar plates in PEMFC.

ON-State Contact Resistance and Arc-Less Commutation Characteristics of Cu-W Clad Contact Materials in a Hybrid DC Switch

Hybrid dc switches have better performance with regard to energy conservation and less arc erosion than conventional semiconductor switches and mechanical switches. A novel hybrid dc switch based on a SiC-MOSFET is developed, and it accomplishes arc-less commutation if the current is below a threshold value, which is mainly determined by the boiling voltage of its contact material. However, as it is difficult for common contact materials to have both a low ON-state contact resistance and high boiling voltage, optimization of the contact materials is necessary to further decrease the ON-state contact resistance and improve the arc-less commutation characteristics of hybrid dc switches. New-type Cu-W clad contacts are proposed in this article by brazing tungsten top layers on copper bulks. The performance of the Cu-W clad contacts with the tungsten top layers of different thickness is evaluated by comparing their ON-state contact resistance and the threshold current of arc-less commutation with those of copper contacts and tungsten contacts under dc current ranging from 100 to 400 A. The results of the experiments show that the Cu-W clad contacts with the tungsten top layers of 1 mm thickness are the most suitable for arc-less hybrid dc switches because of their low ON-state contact resistance and largest threshold current of arc-less commutation.

Study on Contact Resistance Characteristics of Electrical Connectors of Power Battery Module

Study on Contact Resistance Characteristics of Electrical Connectors of Power Battery Module

Simulation of the Thermal Contact Resistance Characteristics on Rod Fastening Rotor

The thermal contact resistance model of the rod fastening rotor is improved, which can be more suitable for the engineering condition. By means of numeric simulation, the relationships between characteristics of the heat transfer between contact interfaces and the pre-tightening force of the tie rod, the surface roughness and the temperature of the contact interface are revealed intuitively. The simulation results show that the coefficient of contact heat transfer between the contact interfaces will increases with the pre-tightening pretension of the tie rod, will decreases with the increase of the surface roughness, and will increases with the increase of the surface temperature. It is also shown that the thermal contact resistance between the contact interfaces will have an important influence on the overall temperature distribution and heat transfer of the rod fasten rotor, and the thermal contact resistance between the interfaces must be considered when the temperature field distribution of the rod fastening rotor are accurately researched.

Two-Dimensional-Like Amorphous Indium Tungsten Oxide Nano-Sheet Junctionless Transistors with Low Operation Voltage

In this work, we have successfully demonstrated the junctionless (JL) transistors with two-dimensional-like (2D-like) nano-sheet (NS) material, amorphous indium tungsten oxide (a-IWO), as an active channel layer. The influences of the different gate insulator (GI) materials and the scalings of GI thickness, a-IWO channel thickness, and channel lengths on the a-IWO NS JL transistors (a-IWO NS-JLTs) have been studied for the purposes of low operation voltage (gate voltage ≤2V) and high performance. The 2D-like a-IWO NS-JLTs exhibit low operation voltage, low source/drain (S/D) contact resistance (RC) and other key electrical characteristics, such as high field-effect mobility (μFE), near ideal subthreshold swing (S.S.), and large ON/OFF currents ratio (ION/IOFF). The remarkable device characteristics also make the proposed 2D-like a-IWO NS-JLTs promising for system-on-panel (SoP) and vertically stacked (VS) hybrid CMOS applications.

Study on the Contact Performance of Electronic EON Connectors Under Axial Vibration

One of the main failure mechanisms of electronic connectors is fretting wear induced by vibration. In this paper, three connectors having different eye-of-needle (EON) pins were investigated for their mating and vibration performances with assembling of different sized and surface-treated printed circuit boards (PCB). In addition to experimental measurement, quasi-static finite-element analysis was also employed in the study of the mating between the EON pin and PCB hole. The results indicated that the retention force was higher when the EON pin was assembled with larger sized hole under lower bound specification. Therefore, higher retention force can be maintained by using appropriate-sized hole or interference. Moreover, according to analysis of variance based on the performance characteristics of retention force and electrical contact resistance, the significance of design factors, i.e., PCB hole size and surface treatment, could be evaluated. Finally, in the vibration test, the sinusoidal excitation level was normalized in accordance with the above experimental results in the retention force of each connector. It was found that under the constant EON size, hole size was the significant control factor in the retention force of mating pair. On the other hand, surface treatment was the significant control factor in the electrical contact resistance. Under vibration test, the control factor of surface treatment on the PCB panel was more significant in determining the electrical contact resistance of the connector than the interference factor.

Method of electrical connector intermittent fault reproduction

PurposeThis paper aims to reproduce the electrical connector intermittent fault behaviours with step-up vibration stress while maintaining the integrity of the product. Design/methodology/approachA dynamic model of an electrical connector under vibration is established for contact resistance analysis. Next, the dynamic characteristics of contact resistance are analysed, and cumulative damage theory is used to calculate the damage under different stresses during the intermittent fault reproduction test. To reduce damage and improve efficiency, the step-up stress is used for the reproduction test. FindingsThe proposed method can reproduce the intermittent fault behaviour, and the step-up stress test is more efficient than the constant stress test. Research limitations/implicationsStep-up stress is used for intermittent fault reproduction, and the quantitative relationships between intermittent fault and product damage can be further studied. Practical implicationsIt is expected that the proposed methodology can help engineers to reproduce the intermittent fault behaviours to facilitate the detection and diagnosis of intermittent fault and to improve equipment safety. Originality/valueThe mechanism of electrical connector reproduction is analysed and the step-up stress test is used for intermittent fault reproduction.

Polymer-Free Electronic-Grade Aligned Semiconducting Carbon Nanotube Array.

Conjugated polymers are used commonly to selectively sort semiconducting carbon nanotubes (S-CNTs) from their metallic counterparts in organic solvents. The polymer-wrapped S-CNTs can be easily processed from organic solvents into arrays of CNTs for scalable device fabrication. Though the conjugated polymers are essential for sorting and device fabrication, it is highly desirable to remove them completely as they limit the electronic properties of the device. Here, we use a commercially available polymer, namely, poly[(9,9-dioctylfluorenyl-2,7-diyl)-alt-co-(6,6'-(2,2'-bipyridine))] (PFO-BPy), to sort large-diameter S-CNTs with ultrahigh selectivity and fabricate CNT-array-based field effect transistors (FETs) via a floating evaporative self-assembly (FESA) process. We report quantitative removal of the polymer wrapper from the FESA aligned S-CNT arrays using a metal-chelation-assisted polymer removal (McAPR) process. The implementation of this process on FESA films requires the selective thermal degradation of the polymer into oligomers, combined with optimization of the solvent type and temperature of the metal complexation reaction. Resulting S-CNT array FET devices show that the electronic properties of pristine CNT are preserved through this process. Optical microscopy, UV-vis spectroscopy, and X-ray photoelectron spectroscopy (XPS) were used to characterize the quantitative polymer removal. We quantitatively describe the FET devices to analyze the fundamental characteristics of FETs (mobility (μ), on-conductance (Gon), and contact resistance (2Rc)) by comparing before and after polymer removal. The ability to completely remove the polymer wrapper in aligned CNT arrays without adversely affecting the device properties opens up applications beyond FETs into photovoltaics and biosensing.

An analytical solution for contact resistance of staggered organic field-effect transistors

We have developed analytical models for bias dependent contact resistance (RC) and output characteristics of staggered organic field-effect transistors (OFETS) based on a bulk resistance-approximated and mobility-modified current-crowding method. Numerical evaluations of RC and its resistive components show that the bias dependency of the bulk resistance is negligible. Consequently, the properties of the active layer interfaces determine RC and its characteristics. Effective parameters include a normally constant charge injection barrier at the organic-metal interface (Eb) and a gate induced surface carrier-concentration (PS0) at the organic-insulator boundary. The energy barrier pertains to the fabrication process, and its related resistance (rc) can be determined as the fitting parameter of the theoretical model. However, PS0 is strongly gate bias dependent and the results of the numerical model indicate that the resulting component (rch) is dominant and has a considerable effect on RC and its characteristics. More importantly, PS0 as the key parameter of the contact resistance is analytically expressible and by using a proposed mobility-modified current-crowding model, the contact resistance can be analytically formulated. Accordingly, the output characteristics of the OFETs in the triode region can be also analytically modeled using the developed relation of RC.

Phase change memory employing a Ti diffusion barrier for reducing reset current

Phase Change Memory (PCM) has the potential for use as the flash memories for the next generation due to its scalability, long endurance, high speed, and the possibility of random access. To successfully integrate phase change materials of a GeSbTe (GST) alloy in the device fabrications, the presence of a Ti layer is required to obtain proper contact resistance characteristics and also to improve the adhesion property between the GST alloys and the top TiN electrode. The findings reported herein indicate that Ti can readily diffuse into the GST layer and reduce the set resistance when the subsequent device fabrication involves the heating process. As a result, the reset current significantly increases and the endurance cycles of the PCM device are significantly degraded. We proposed the use of a Highly Nitrogen doped GST (HNGST) layer as a barrier to Ti diffusion, in which the presence of the barrier was able to restore the reset current of the PCM devices down to the level of as-etched PCM cell by the use of a 9nm thick HNGST barrier. In addition, endurance cycles were significantly enhanced from 106 to over 108 by blocking the diffusion of Ti into the program volume of the cell with the HNGST barrier layer.