Electrical Contacts

The purpose of this work is to discuss the tulip contact behavior during mechanical and electrical simulations in a Finite Element Method (FEM) environment using ANSYS and COMSOL software. During the simulations, the full contact movement was analyzed. During the contact movement, the individual behavior of the contact components was taken into consideration. The motion simulation was carried out at different velocities and forces acting on the contact. The obtained results were compared to each other and discussed. Relatively, the angles of the contact surfaces to each other were also changed, which meant that we could conduct a more in-depth analysis. The other approach of simulation research was a field analysis of physical phenomena occurring in the tulip contact. This analysis was performed in COMSOL Multiphysics. Parametric analysis allowed an observation of the electric field in the tulip contact at different contact distances with respect to each other. This work is importan...

There is considerable interest in the corrosion control of thin gold plated contact surfaces of consumer electronics products. This originates in the desire to minimize the use of costly gold and other precious metals, like palladium, and their alloys, without sacrificing reliability. When the application is in adverse environments, gold plated contact finishes can enhance the reliability of the electrical contacts. However, the failure mechanisms depend strongly on the operating environment and contact plating and are time dependent processes. Numerous investigations on unloaded gold plated surfaces (unmated and tested at non-operating environmental condition) have been performed to simulate the contact failures induced by corrosion. However, no models have been proposed that account for the effects of loading electrically and mechanically on the corrosion process and selection of gold plating thickness. This article describes the study of loaded electrical contacts with the objective of setting up a comparative model between unloaded and loaded electrical contacts, which will improve the understanding of the influence of contact force and applied voltage on the selection of gold layer thickness and finish material. Contact force will improve the performance of gold finishes in stationary electrical contacts and decrease significantly, the gold plating thickness requirements compared to unloaded situation because of its effect on suppression of surface film growth. Voltage will accelerate the growth of surface film and result in the decrease of contact lifetime. ᭧

Magnetic blow-off forces play an important role in arcing and failure of electrical joints and contacts in electrical systems under high current fault conditions. Magnetic blow-off forces arise from concentration of current in the contact interface and tend to blow the contacts apart, causing separation and arcing. Simple models have been developed to predict the magnitude of these forces and permit the design of joints and contacts that can successfully resist the forces. In this paper, the role of magnetic blow-off in railgun armature contacts is explored. It is shown that magnetic blow-off forces are important and may be the final step in a series of events that ultimately leads to transition. Models that predict the conditions under which blow-off will occur are developed, and supporting experimental data is described.

S/DRM testing methods usually use long, heavy cables to connect high current source from ground to the circuit breaker. Alternative is to move current source close to the circuit breaker by using heavy batteries, transformers, dc/dc etc. In new proposed method batteries are replaced with ultra capacitors and constant current charger, resulting in a few hundred grams of powerful current source, capable to generate few hundred amperes into the breaker contacts, or any other power contacts. Measuring voltage drop across the circuit breaker and the current through it continuously monitors discharging of ultra capacitors, giving a high accurate resistance value of the measured object.

Eu RoHS Directive for environmental and health concerns have resulted in significant activities to find substitutes for lead-contained solders for microelectronics. The potential candidates such as Sn-Ag 1 and Sn-Ag-Cu 1 eutectic solders with melting temperatures of 221°C and 217°C, respectively are the most prominent solders because of their excellent mechanical properties as compared with that of eutectic Sn-Pb solder2. Other candidates as drop-in replacements for eutectic Sn-Pb solder, such as Sn-In-Zn alloys, may have melting point close to 185°C, though not eutectic, and an acceptable solidification range but have received only limited attention 1. Among the many possible lead-free solder alloy candidates, three commonly used alloys to meet automotive thermal cycling requirement are Sn3.0Ag0.5Cu, Sn3.8AgO.7Cu and Sn4.0Ag0.5Cu. However, industry has found these commonly applied solder alloys to have certain level of ball drop problem which affects production yield, product quality as well as customers satisfaction. This paper reports a study which was conducted on BGA lead-free C5 solder joint system to compare SnAgNiCo solder alloy versus the conventional Sn3.8AgO.7Cu solder alloy, with the objective to strengthen the solder joint so as to eliminate ball drop encountered on the conventional Sn3.8AgO.7Cu solder alloy. This study showed that SnAgNiCo C5 solder system performed better than Sn3.8AgO.7Cu in terms of joint strength and intermetallic brittle mode failure rate. Experimental works were carried out to observe the melting properties, micro structure and elemental analysis that were obtained by Differential Scanning Calorimetry (DSC), SEM and EDX respectively. Shear and pull strength was measured by Dage which is representative of solder joint strength between the C5 solder sphere and Cu/Ni/Au pad finishing. Drop Tests were done per Tray & Packing methods to gauge solder joint performance against impact force. A comprehensive study was done to study the effect of microstructure and interface intermetallic of both solder system at ambient, high temperature storage (HTS) at 150°C for 168 hours and 504 hours, and 6× multiple reflow towards the joint integrity. Microstructure studies on SnAgNiCo solder reveals that formation of rod shape Ag 3Sn IMC distributed across the solder surface helps to act as dispersion hardening that increases the mechanical strength for the SnAgNiCo solder. Through the microstructure study with SEM, it was also found that the addition of Ni and Co into the SnAg solder alloy also helps to minimize growth of grain size and prevent increase in intermetallic thickness after thermal aging. EDX analysis confirmed that in SnAgCu solder/Ni interface, Cu-rich IMC formed on top of the Ni-rich IMC. For SnAgNiCo system, only Ni-rich IMC is found. Therefore, it is highly suspected that the presence of Cu-rich IMC posed a detrimental effect on the joint strength and tends to cause brittle joint failure. Both of the effect is then showed in ball pull result that at Time Zero after assembly and after 6× reflow, SnAgCu solder has 90% and 100% brittle mode failure, where SnAgNiCo solder has 0% and 5% for the respective read points. This result correlates with missing ball responses after packing drop tests which shows no failure for SnAgNiCo alloy. Thus, SnAgNiCo lead-free solder is a potential candidate for lead-free solder joint improvement for overall lead-free package robustness.

http://ieeexplore.ieee.org/xpls/abs_all.jsp?arnumber=4763497&tag=1

This paper presents a method, which the author proposes to call Percentage Correlation Technique, for interpolating a curve between two known curves, which have a direct relationship to a second set of curves, whose functions are known. Although, the method itself is a variation of linear interpolation technique, the curve functions of all curves can be either linear or non-linear. It is shown how this method is applied in a real world application of calculating electrical contact resistance of digital interconnect socket pins.

We report the fabrication of single and few-channel carbon nanotube (CNT) Schottky diodes on high-frequency compatible substrates using horizontally aligned CNT arrays and dissimilar metal contacts in a coplanar-waveguide geometry. Rectification of ac signals in the range of 100 MHz-40 GHz is examined and the observed cutoff frequencies are used to compute the Schottky junction capacitance of the devices, which is strongly CNT-length-dependent and appears dominated by stray capacitance between the CNT channel and metal electrode, in agreement with electrostatic simulations.

Environmental and health concerns have resulted in significant activities to find substitutes for lead-contained solders for microelectronics. The potential candidates such as Sn-Ag1 and Sn-Ag-Cu1 eutectic solders with melting temperatures of 221°C and 217°C, respectively are the most prominent solders because of their excellent mechanical properties as compared with that of eutectic Sn-Pb solder2. Other candidates as drop in replacements for eutectic Pb-Sn solder, such as Sn-In-Zn alloys, may have melting point close to 185°C, though not eutectic, and an acceptable solidification range but have received only limited attention due to various reasons & concerns1. In semiconductor packaging industry, lead-free solders such as Sn-Ag1 and Sn-Ag-Cu1 have been widely applied in mass production of ball grid array products. Such alloys are often used for C5 solder system. However, one of the major challenges is oxidation after thermal processing such as reflow, burn-in, data retention bake and hot temperature testing. A study was conducted on BGA lead-free C5 solder joint system to assess the effect of Germanium (Ge) addition to Sn3.5Ag and Sn3.8Ag0.7Cu solder alloy. The main objective of this study is to find a way to resolve solder surface oxidation after thermal processes, while determining if there's any adverse effect on the solder joint by Ge addition. Experimental works were carried out to observe the melting properties and solder surface morphology by Differential Scanning Calorimetry (DSC) and SEM. Solder surface oxidation was measured by EDX. Shear and pull strength was measured by Dage which is representative of the intermetallic (IMC) strength between the C5 solder sphere and Cu/Ni/Au pad finishing. Solderability test was conducted per Jedec standard. Tray and Packaging Drop Tests were done to gauge solder joint performance against impact force. A comprehensive study was done to study the effect of microstructure and interface intermetallic of both solder system at ambient, high temperature storage (HTS) at 150°C for 24, 48, 96, 168, 504 and 2000 hours and multiple reflow of 1x, 2x, 3x, 6x towards the joint integrity. Overall, Ge doped alloys had significantly higher ball shear and ball pull strength. EPMA microstructure analysis after cross-sectioning on bulk solder and IMC revealed traces of Ge that contributed to the significant increase in ball shear and ball pull strength, while did not cause any bulk solder and IMC morphology changes. Solderability test passed. Drop tests had comparable performance as non Ge doped alloys. In conclusion, addition of Ge in Sn3.5Ag and Sn3.8Ag0.7Cu lead-free solder alloys is able to resolve surface oxidation problem after thermal processing, with improvement in solder joint strength for overall lead-free package robustness.

http://ieeexplore.ieee.org/xpls/abs_all.jsp?arnumber=5416568&tag=1

Thin films of contact metals, specifically Au, Ir, Cr, and Sc, are deposited on exfoliated, bulk MoS 2 using electron beam deposition under two different reactor base pressures to determine the contact metal−MoS 2 interface chemistry and its dependence on the reactor ambient. The high work function metal Au does not react with MoS 2 regardless of reactor ambient. In contrast, interfacial reactions between MoS 2 and another high work function metal, Ir, are observed when it is deposited under both high vacuum (HV, ∼ 1 × 10 −6 mbar) and ultrahigh vacuum (UHV, ∼ 1 × 10 −9 mbar). Interfacial reactions occur between metals with low work functions (Cr, Sc) near the electron affinity of MoS 2 when the contact metal is deposited under UHV conditions. In addition, Sc is rapidly oxidized on the MoS 2 surface, whereas Cr is only partially oxidized when deposited under HV conditions. This indicates that deposition chamber ambient can affect the contact metal chemistry in addition to the chemistry present at the contact metal−MoS 2 interface. These results elucidate the true chemistry of some contact metal−MoS 2 interfaces and its dependence on the deposition ambient, and highlight the need to consider the chemical states present at the interface and their impact on contact resistance with MoS 2 .

The limited lifetime in a high current is the main drawback of spark-gap switches. Electrode replacement is an easily suggested method to extend the lifetime. In order to perform electrode replacement, thermal damage caused by heating effect should be prevented at the static electrical contact interfaces between the electrodes and the holders. Based on the Holm model, the Hertz formula, and the heat conduction theory, a mathematical model of the contact temperature rise is proposed in this paper. This mathematical model can prove quantitatively that the pulse-current integral (action integral), material physical properties, and mechanical characteristics of spark-gap switches are key parameters affecting the temperature rise. The action integral is determined by the electrical parameters. Material physical properties include the thermal conductivity, the specific heat, the density, the electrical resistivity, the elasticity modulus, and the Poisson ratio. Mechanical characteristics of spark-gap switches include the contact radius/area, the contact force, and the contact surface roughness. The implementation of electrode replacement depends on the reasonable configuration of these key parameters. The experiments in a 1.2-MJ power supply module give that the phenomenona correspond with our analysis. Based on the analysis in this paper, an electrode holder structure is proposed as a practical solution for extending the useful lifetime of spark-gap switches with graphite electrodes.

The formation of the Ti−MoS 2 interface, which is heavily utilized in nanoelectronic device research, is studied by X-ray photoelectron spectroscopy. It is found that, if deposition under high vacuum (∼1 × 10 −6 mbar) as opposed to ultrahigh vacuum (∼1 × 10 −9 mbar) conditions are used, TiO 2 forms at the interface rather than Ti. The high vacuum deposition results in an interface free of any detectable reaction between the semiconductor and the deposited contact. In contrast, when metallic titanium is successfully deposited by carrying out depositions in ultrahigh vacuum, the titanium reacts with MoS 2 forming Ti x S y and metallic Mo at the interface. These results have far reaching implications as many prior studies assuming Ti contacts may have actually used TiO 2 due to the nature of the deposition tools used.

This paper presents experimental results on the influence of contact opening velocity and the moment of contact oipening with respect to the start of the ac current cycle on arc energy and contiact erosion when breaking an ac resistive circuit. The test currents are 5.6 A,, 14.7 A and 26.3 A, and the contact material is Ag/CdO (90/10). A computer controlled test system allows the control of the contact velocity profiles with constant velocities up to 0.8 m/s, and also enables the synchronization of the contact opening with a point on the ac current waveform. Contact erosion is evaluated by measuring the mass loss or gain changes of the cathode and anode.

Electrical contact resistance between bipolar plates of PEM fuel cells has attracted much attention since it is one significant part of the total contact resistance which plays an important role in fuel cell performance. The effect of contact pressure on the bipolar plates electrical contact resistance is discussed in this paper. Various roughness on the bulk surface and various ingredient percentages of the adhesive compound were considered. The experimental results show that the contact resistance between bipolar plates has a minimum for appropriate values of contact pressure, plate surface roughness and ingredient percentages of the adhesive compound.

Electrode replacement is an effective method to extend the useful lifetime of the spark gap switch with graphite electrodes. In order to perform electrode replacement, suppressing temperature rise and preventing static welding/erosion should be considered for the static electrical contact interface between the electrode and the holder. In this paper, a mathematical model of contact temperature rise is proposed based on the Holm model and heat-conduction equations. This mathematical model can quantitatively prove that some material properties of the metal holder and some mechanical characteristics of the spark gap switch are key parameters affecting temperature rise. Material properties of the metal holder include thermal conductivity, specific heat, density, electrical resistivity, elasticity modulus, and the Poisson ratio. Mechanical characteristics of the spark gap switch include contact radius/area, contact pressure, and contact surface roughness. Optimum configuration of these key parameters reduces temperature rise and prevents static welding/erosion.

This work mainly deal with reducing friction and wear caused by adhesion and plowing on a non-lubricated connector contact surfaces. To eliminate friction an electrical connector interface is developed in order to obtain low contact resistance. Other traditional methods are by lubrication of the interface and to increase the surface hardness of one surface. These materials eliminate wear particles from the interface before they agglomerate and hence result in significant reduction of friction and wear. Multiple points of contact interface to make good electrical contact even in highly contaminated environments with very low normal forces. The friction is low because of the near absence of plowing that contributes to friction.

Electrical contacts are expected to be influenced by coupled thermo-electro mechanical mechanisms. In this paper a single spherical asperity contact has been investigated with a coupled finite element thermo-electro mechanical approach. Thermo-electro mechanical behavior of a sphere in contact with a block has been analyzed while focusing on the effect of plastic deformation and thermal expansion. A finite element model is developed to analyze different cases and various parameters. Stress distribution, voltage drop and temperature profile have been presented. Results suggest that the thermal expansion influences the contact resistance significantly only for cases where the interferences are small. The thermal expansion decreases the contact resistance at a given interference, probably by effectively increasing the contact force. A non-dimensional parameter is derived to predict whether or not the influence of thermal expansion is important on an electrical contact.

A 3-D domain decomposition method for fully coupled electrothermomechanical contact problems is presented. The formulation is based on the cell method. Contacting domains are linked together by introducing a new reference frame (i.e., the mortar surface). Field discontinuities across contact interfaces are simulated by suitable constitutive operators. It is shown that the same coupling strategy can be adopted for the electrical, thermal, and mechanical contact problems. Compatibility constraints are imposed by means of dual Lagrange multipliers defined on the mortar surface. Coupled nonlinear algebraic equations are finally cast into a saddle-point problem, which is resolved by combining the Schur complement method with the Newton-Raphson method. The proposed mortar approach is validated with a commercial 3-D finite-element method multiphysics software package.

An electromagnetic system that operates both as a rail and as a coil launcher is proposed, and its performance is analyzed. The device has a composite stator that consists of two rails properly slotted in order to allow the presence of a system of coils. The armature consists of a conductive slab sliding between the rails. Another system of slots is present in the armature where a system of short-circuited coils is placed.

This paper presents a design of RF MEMS contact switch with high isolation, low insertion loss, small chip area and low power consumption. The switch is fabricated by standard 1P6M 0.18μm CMOS process from TSMC which is compatible with CMOS process. A dc-bias voltage is applied between the cantilever beam and bottom electrode. The switch is actuated by electrostatic force that drove the tail of the cantilever beam contact with the transmission line. In order to avoid RF signal loss, DC and RF signal are separated by SiO 2. The simulation results show that SiO 2 can effectively avoid RF signal loss. The spring structure of cantilever can effectively reduce the driving voltage and improve residual stress (used by the warpage problem.) The cantilever structure of switch is based on aluminum and the scarified layer is used by the aluminum and silicon oxide. RIE etching was applied to remove the scarified layer of silicon oxide to form wet etching channels. So, the structure was easy to be released by wet-etching. At last, the supercritical CO 2 drying was used to release the structure (annoying stiction problem.) Finally, we successfully demonstrate the fabrication of RF MEMS contact switch by standard 1P6M 0.18μm CMOS process from TSMC. Also, the post-processing is implemented to manufacture the RF MEMS contact switch. The proposed RF MEMS contact switch can be used in microwave CMOS RF front-ends where multiband functionality and reconfigurability is required. The measurement results as below, the pull-in voltage of RF MEMS contact switch is 2.8V, isolation is-60dB, respectively. Since the CMOS silicon has a very low resistivity (8Ω cm), it will increase the isolation of RF MEMS contact switch. So, the Metal_1 layer is designed as ground which could greatly improve isolation.

Results for a reconfigurable PIFA using smart materials are presented. A novel approach is investigated by using PZT materials that switch into contact using a dc control voltage to reconfigure the PIFA structure and hence produce a tunable antenna.

In a range of energy systems, interfacial characteristics at the finest length scales strongly impact overall system performance, including cycle life, electrical power loss, and storage capacity. In this letter, we experimentally investigate the influence of surface topology on interfacial electro-mechanical properties, including contact stiffness and electrical conductance at rough surfaces under varying compressive stresses. We consider different rough surfaces modified through polishing and/or sand blasting. The measured normal contact stiffness, obtained through nanoindentation employing a partial unloading method, is shown to exhibit power law scaling with normal pressure, with the exponent of this relationship closely correlated to the fractal dimension of the surfaces. The electrical contact resistance at interfaces, measured using a controlled current method, revealed that the measured resistance is affected by testing current, mechanical loading, and surface topology. At a constant applied current, the electrical resistance as a function of applied normal stress is found to follow a power law within a certain range, the exponent of which is closely linked to surface topology. The correlation between stress-dependent electrical contact and normal contact stiffness is discussed based on simple scaling arguments. This study provides a first-order investigation connecting interfacial mechanical and electrical behaviour, applicable to studies of multiple components in energy systems.

The proposed system is suitable for current-mode segmented intercell bars. Previous developments show that these bars provide protection against short circuits but are sensitive to open circuits and dirt contacts. This new system adds segmented sidebars to interconnect in groups the otherwise electrically insulated cathode and anode hanger ends. The combination of a segmented main bar with these sidebars offers protection against short circuits, open circuits, and impaired contacts.

We study recombination properties and the formation of base contacts, which are realized by local laser ablation of a dielectric stack and the subsequent full-area screen printing of an Al paste. Based on charge-carrier lifetime measurements using the camera-based calibration-free dynamic infrared lifetime mapping technique, we determine contact reverse saturation current densities as low as J 0,cont = 9 × 10 2 fA/cm 2 on 1.5-Ωcm p-type float-zone silicon (FZ-Si) and J 0,cont = 2 × 10 4 fA/cm 2 on 200-Ωcm p-type FZ-Si. Scanning electron microscopy images reveal that the thickness of the highly Al-doped (Al-p + ) layer considerably depends on the contact size and the contact layout (e.g., point or line contacts). Based on this finding, we show that Al-p + layer thickness W Al−p+ significantly affects the contact recombination. As a result, we show which local contact geometry is most appropriate for the lowest contact recombination employing local Al-alloyed contacts.

An electromagnetic system that operates both as a rail and as a coil launcher is proposed, and its performance is analyzed. The device has a composite stator that consists of two rails properly slotted in order to allow the presence of a system of coils. The armature consists of a conductive slab sliding between the rails. Another system of slots is present in the armature where a system of short-circuited coils is placed.

The purpose of this paper is to investigate the thermoelectrical behaviour of ohmic microcontacts under low force. The temperature in the contact zone is very important for the reliability of microswitches. As it is very difficult to measure the inner temperature, the numerical thermal modelling of electrical contacts offers interesting perspectives. A multi-physics modelling of electrical contact is accomplished with the finite element commercial package ANSYS TM . Two approaches for coupled-field analysis are investigated, namely direct and load transfer. The thermo-electro-mechanical modelling is firstly validated with a smooth sphere-plane contact, and then applied for a real rough contact computation, elastic-plastic material deformation is included in the modelling. The temperature distribution on the contact surface is plotted, and the maximum temperature is found around the asperities with the highest deformation. The multi-physics model offers a reliable method to investigate the steady-state thermal behaviour of electrical contact with rough surface included.

This paper explores contact heating in microelectromechanical systems (MEMS) switches with contact spot sizes less than 100 nm in diameter. Experiments are conducted to demonstrate that contact heating causes a drop in contact resistance. However, existing theory is shown to over-predict heating for MEMS switch contacts because it does not consider ballistic transport of electrons in the contact. Therefore, we extend the theory and develop a predictive model that shows excellent agreement with the experimental results. It is also observed that mechanical cycling causes an increase in contact resistance. We identify this effect as related to the build-up of an insulating film and demonstrate operational conditions to prevent an increase in contact resistance. The improved understanding of contact behavior gained through our modeling and experiments allows switch performance to be improved. [1424] Index Terms-Electrical contacts, microelectromechanical systems (MEMS), switches.

This paper describes experiments to measure melt-wave erosion (MWE) damage in railgun armatures. C-armatures were launched on the Medium Caliber Launcher at the Institute for Advanced Technology (IAT), Leander, TX, and recovered by "soft catching" in a tube filled with cotton rags. Recovered armatures were mechanically profiled to measure erosion depth as a function of position on the contacting surfaces. Although recovered armatures provide only a final snapshot of the erosion process, one can show how erosion proceeds by recovering armatures at different stages of the launch. This type of study requires the use of a crowbar switch at the breech of the railgun to rapidly shunt current out of the armature, thereby interrupting the erosion process at the desired point in the launch. We describe the experimental setup and summarize the results of 11 experiments. The experiments investigated the effect of linear current density (ranging from 35 to 45 kA/mm) and rail material (copper and aluminum) on MWE damage. Lastly, we present some thoughts on contact transition mechanisms that, in some cases, prevented the collection of MWE data.

This paper demonstrates the efficiency of a new methodology using a commercial nanoindenter coupling with electrical measurement on test vehicles specially designed to investigate the micro contact reliability. This study examines the response of gold contacts with 5 mum2 square bumps under various levels of current flowing through contact asperities. Contact temperature rising is observed leading to shifts of the mechanical properties of contact material, modifications of the contact topology and a diminution of the time dependence creep effect. The data provides a better understanding of micro-scale contact physics especially failure mechanisms due to the heating of the contact on MEMS switches.

We investigate the challenges and potential for highefficiency n-type Cz Si solar cells having a hybrid structure -a diffused B emitter on the front side, and an amorphous Si heterojunction (SHJ) passivated full-area contact on the rear. This cell design has benefits over comparable high-efficiency geometries such as PERL (passivated emitter rear locally diffused) and SHJ cells with heterojunctions both front and rear. We show that an advantage of the HJ rear contact is excellent passivation of the backside, with measured contact recombination current density J 0,b,c < 10 fA/cm 2 ; moreover, compared to PERL, its cell fabrication process is much simpler. Weighed against standard SHJ cells, the diffused front results in less optical loss and no need for a transparent conducting oxide (TCO). We study the contact resistivity of a state-of-the-art SHJ rear contact to the wafer, finding a value of ~0.3 ohm-cm 2 ; a series of experiments are performed to reduce this value while maintaining potential for high V oc > 700 mV.

The parasitic factors that strongly influence the measurement accuracy of Cross-Bridge Kelvin Resistor (CBKR) structures for low specific contact resistances ( c ) have been extensively discussed during last few decades and the minimum of the c value, which could be accurately extracted, was estimated. We fabricated a set of various metal-to-metal CBKR structures with different geometries, i.e., shapes and dimensions, to confirm this limit experimentally and to create a method for contact metal-tometal interface characterization. As a result, a model was developed to account for the actual current flow and a method for reliable c extraction was created. This method allowed to characterize metal-to-metal contact interface. It was found that in the case of ideal metal-to-metal contacts, the measured CBKR contact resistance was determined by the dimensions of the two-metal stack in the area of contact and sheet resistances of the metals used.

In recent times WCAg has become one of the preferred contact materials in vacuum contactors for switching load currents of some hundred Amperes up to a few kiloamperes. It meets the requirements of vacuum contactors such as low erosion losses, low chopping currents, a sufficient quenching capability etc. satisfyingly. Today's efforts try to reduce the percentage of the expensive silver component in this material or to substitute it. In this contribution the effects of changing the percentages of Ag and WC as well as the substitution of Ag with Cu is discussed and the switching behavior described. The different materials will be compared with respect to their breaking capability, their chopping current, their erosion losses and the state of their contact surfaces after arcing. The experiments were carried out with a demountable vacuum chamber in a synthetic test circuit. For the switching capability tests the contacts were stressed by arc currents up to 7 kA RMS and a transient recovery voltage of 23 kV peak. The chopping measurements were carried out at a test current of 45 A RMS in a test circuit with a resonant frequency of 6800 Hz and a surge impedance of 1066 Ohms.

Rough surface contact is difficult to model effectively due to multiple scales of detail that need to be considered. This work presents the results of a multiscale rough surface contact model in comparison to a finite element based deterministic model for the electrical contact of a MEMS microswitch. The real area of contact and electrical contact resistance are predicted and compared as a function of normal load. The results show good quantitative and qualitative correlation between the two methods.

A series of experiments was performed to characterize RF microelectromechanical system switch performance under variable environmental conditions and cryogenic temperatures. Data were recorded in helium and nitrogen environments to lower stiction failure rates as well as to circumvent switch bouncing arising from low pressure at cryogenic temperatures. Contact resistance values were observed to be lower at cryogenic temperatures but still two orders of magnitude higher than the values predicted for the constriction resistance of gold asperity contacts, consistent with the presence of adsorbed films on the contacts. An asperity-heating model was applied, from which it was deduced that contact voltages can selectively disassociate adsorbed films from the contact surface while not softening the gold asperity contacts. The results are consistent with the reduced mobility of the adsorbed surface films at cryogenic temperatures. [2007-0217] Index Terms-Contact resistance, electrical contacts, microelectromechanical systems (MEMS), RF MEMS, switches.

English translation of Eberhard Contius' classic original PhD dissertation in German from 1929 on The Influence of Total Pressure and Area on Contact Resistance. This was the first monumental work in the research of electrical contact resistance.

To improve energy efficiency in copper electrowinning, different technologies have been developed. These include electrode positioning capping boards and 3-D grids, electrode spacers, and segmented intercell bars. This paper introduces a design concept to avoid electrode open circuits and reduce contact resistances. The design is based on a female tooth shape for the contacts on the intercell bar. This leads to improved electrode alignment, reduced contact resistances, easier contact cleaning, and ensured electrical contact for the electrodes. It results in lower operational temperature for the electrodes, reduced plant housekeeping, increased lifespan for capping boards, and higher rate of grade A copper production. The comparative results presented should be a useful guideline for any type of intercell bar. Improvements in production levels and energy efficiency should reach 0.5% and 3%, respectively. A 3-D finite-element-based analysis and industrial measurements are used to verify the results.

In the past years the vacuum switching principle has gained wide acceptance in medium voltage systems. While vacuum circuit breakers, where high short-circuit currents have to be mastered, nearly exclusively utilize CuCr 25 wt.-% to 50 wt.-% as contact material, the choice in vacuum interrupters for switching lower load currents (e.g. contactors) is less definite. The material must meet the requirements of low erosion losses on a high number of switching operations, low chopping currents, low tendency to generate HF transients and a satisfying quenching capability as well. Often materials based on refractory components are used, such as WCu, MoCu, WCAg, but also CuCr seems applicable. The aim of this work has been to investigate such contact materials with respect to their interrupting behavior on load and overload conditions. The experiments were carried out with a vacuum test chamber in a synthetic test circuit. The contacts were stressed by arc currents up to 7 kA RMS and a transient recovery voltage of 23 kV PEAK. Different contact materials have been compared with respect to their breaking capability and the state of their contact surfaces after arcing by means of scanning electron microscopy.

This paper shows a new possibility for quality and reliability testing of low-current contacts by nonlinearity measuring. A normal third harmonic distortion (THD) tester cannot be used for low-impedance elements. Therefore, a special variant of the THD tester is described for this aim. This method was proved at a set of relay contacts and the results of testing validate a propriety of proposed method.

The sensing of chemicals and biochemical molecules using several porous silicon optical microsensors, based both on single-layer interferometers and resonant-cavity-enhanced microstructures, is reported. The operation of both families of sensors is based on the variation of the average refractive index of the porous silicon region, due to the interaction with chemical substances either in vapor or liquid state, which results in marked shifts of the device reflectivity spectra. The well established single-layer configuration has been used to test a new chemical approach based on Si-C bonds for covalent immobilization of biological molecules, as probe, in a stable way on the porous silicon surface. Preliminary results on complementary oligonucleotide recognition, based on this technique, are also presented and discussed. Porous silicon optical microcavities, based on multilayered resonating structures, have been used to detect chemical substances and, in particular, flammable and toxic organic solvents, and some hydrocarbons. The results put in evidence the high sensitivity, the reusability, and the low response time of the resonant-cavity-enhanced sensing technique. The possibility of operating at room temperature, of remote interrogation, and the absence of electrical contacts are further advantages characterizing the sensing technique.

Describes some work carried out 0n 240 volts rated snap-action switches. These switches are used typically in thermostatic control systems where there is slow thermally activated prime mover whose movement must be converted into an electric make and break action. Sometimes, switch contacts become severely eroded after many years of use, for example in refrigerators and weld together causing system failure. This first stage of the study involved high speed photography of the snap-action mechanism to determine the break characteristics.

This paper explores contact heating in microelectromechanical systems (MEMS) switches with contact spot sizes less than 100 nm in diameter. Experiments are conducted to demonstrate that contact heating causes a drop in contact resistance. However, existing theory is shown to over-predict heating for MEMS switch contacts because it does not consider ballistic transport of electrons in the contact. Therefore, we extend the theory and develop a predictive model that shows excellent agreement with the experimental results. It is also observed that mechanical cycling causes an increase in contact resistance. We identify this effect as related to the build-up of an insulating film and demonstrate operational conditions to prevent an increase in contact resistance. The improved understanding of contact behavior gained through our modeling and experiments allows switch performance to be improved.