Contact Resistance Data Research Articles

Numerical analysis of the DC performance of ITER TF samples with different cablingpattern based on resistance measurements on terminations

The DC transport properties of ITER TF conductors are analyzed inthe SULTAN facility, but their associated current sharing temperature(Tcs) can give scope for different interpretations. To extract the conductor’s pureperformance during such short sample tests requires a detailed quantitative modelsuch as JackPot, for which as many as possible input parameters are based onexperimentally verified data. The crucial interstrand contact resistance data of theTFPRO-2 and TFJA-3 samples, which have a different cabling and joint layout,has recently become available. With only three parameters for JackPot’s jointmodel, we were able to find a good match between the measured and simulatedinterstrand resistances for all terminations, despite their different layout. ForNb3Sn conductors, the axial strain is the only free model parameter left for matching the simulations withSULTAN Tcs tests. We were able to find a match with the measured voltage–temperature characteristicfor all but one conductor. The simulation results indicate that the termination layout canbe the cause of lower sample performance due to current imbalance. The outcome of thisanalysis also confirms that transverse load degradation can be significantly mitigated byfinding an optimal set of cable twist pitches.

Electrical Characterization of Thin-Film Structures With Redeposited Sidewalls

Accurate electrical characterization of test structures and devices requires identification and correction for parasitic current paths in the measurement network. The sidewalls formed during reactive ion etching of thin-film phase-change material layers in argon plasma can result in parasitic current paths in the structures. In this paper, thin-film structures with redeposited sidewalls are realized, and they are experimentally characterized by electrical resistance measurements on van der Pauw test structures. The impact of conducting sidewalls on contact resistance measurements and data extraction from cross-bridge Kelvin resistor structures is discussed. The error introduced in the electrical resistance measurements from these test structures is analytically modeled. The impact on the electrical performance of devices due to the formation of sidewalls is also discussed.

Copper–beryllium metal fiber brushes in high current density sliding electrical contacts

The use of copper–beryllium (UNS C17200) was demonstrated as a low wear, highly compliant material for the construction of high current density metal fiber brushes. Testing was conducted in a humidified carbon dioxide environment. Brush linear wear rates of 4 × 10 −11 m/m were achieved at sliding speeds and current densities as high as 7.5 m/s and 215 A/cm 2 (2 MA/m 2). Contact resistance values were on the order of 10 mΩ and friction coefficients varied from 0.30 at 2.5 m/s to 0.15 at 7.5 m/s. Characterization of the brush and slip-ring surfaces using SEM as well as the slip-ring subsurface using TEM is presented as evidence in favor of fatigue dominated wear of the copper–beryllium fiber tips. Debris flakes were observed forming on the fiber tips with characteristic widths in the range 10–100 μm and thickness on the order of 1 μm, in stark contrast to 1–10 μm wide flakes of thickness on the order of 1 μm observed forming on the slip-ring surface. Relatively clean contact resistance data at the end of the test is indicative of the robustness of the brush design and the ability of the fiber tips to remain in contact with the evolving slip-ring surface. The importance of material selection, particularly in regard to fatigue and yield strength, is highlighted in this work as key factors in improving brush design and understanding the wear phenomena observed in high current density sliding electrical contacts.

Contact resistance changes of silver, silver alloys, and gold plated silver coupons exposed to ozone

The goal of this research program was to establish the effects of ozone on logic level switching performance and to select materials that would enhance the performance of these switches in the presence of ozone. Initially, four different material systems were examined through a series of experiments using a computer-controlled contact resistance probe. An electronically-controlled ozone chamber was specially designed for this research project. The four different material systems investigated were 85% silver 15% nickel, 90% silver 10% nickel, fine grain silver, and fine silver (.999 pure). Fine grain silver is produced by adding a minute amount of nickel to fine silver. These material systems were exposed to three different ozone levels (0.1 PPM, 7.0 PPM, and 20.0 PPM) and contact resistance data was collected. The ozone level of 0.1 corresponds to approximate ambient levels in switching devices. Higher concentrations of ozone are likely in panels where arcing occurs or in sealed devices. The higher levels of 7.0 and 20.0 PPM ozone used in this project are for accelerated testing purposes. The results of the experiments at ozone levels of 0.1 PPM were not conclusive within the test period, but ozone appeared to have some effect on the contact resistance of the coupons with a higher level of nickel content. Experimentation at 7.0 and 20.0 ozone accelerated the effects of ozone, observed during the experimentation at 0.1 PPM ozone, At 7.0 and 20.0 PPM ozone, the contact resistance data increased as the nickel content in the coupon increased. Although the coupons containing the higher nickel content were more susceptible to an increase in ozone, even the fine silver coupons were attacked. After the experiments on silver and silver-alloys were completed, a study was made to see if soft gold electroplating could offer protection from ozone damage. A set of contact resistance data was collected at 7.0 PPM ozone on fine silver and 85% silver 15% nickel coupons that were plated with 10 and 60 /spl mu/in thick gold. As expected, the contact resistance data for the coupons with a layer of electroplated soft gold were lower than the contact resistance data collected on the uncoated silver coupons. In addition, the contact resistance averages for the coupons with 10 /spl mu/in of gold plating are higher than the contact resistance averages for the coupons with 60 /spl mu/in of gold plating. Therefore, a noble metal protects the surface from the adverse oxidation effects due to ozone and thicker is better.

The effect of fretting at elevated temperatures on a clad material (65Au21Pd14Ag) and an electroplated soft gold over palladium-nickel material system

Fretting experiments were conducted on two different material systems at elevated temperatures. One of the material systems was a clad material. The clad material was an alloy, 120 micro-in thick, consisting of 65% gold, 21% palladium, 14% silver over an 800 micro-in nickel sublayer. The other material system was 40 micro-in of electroplated soft gold over 80 micro-inches of palladium over 80 micro-in of nickel sublayer. Four different temperature levels were used during this research project. The temperature levels were 20, 50, 100, and 200/spl deg/C. Normal force was set at 200 g. Fret amplitude was 50 /spl mu/m. The fretting frequency was 8 Hz. Some limited fretting experiments were conducted using a new contact lubricant (CLT: X-10). Contact resistance data were collected on the number of cycles to reach specific contact resistance levels. These levels were 10, 50, 100, and 250 m/spl Omega/. A four wire milliohmmeter was used to collect the data, A material study was conducted as part of this project. The two different material systems were compared using a simple t-test, based on the number of fretting cycles to exceed 0.25 /spl Omega/. At room temperature, the clad material lasted 10 times as many fretting cycles than the soft gold over palladium material system. At 50 and 100/spl deg/C the clad material was still better than the gold over palladium material system, but the overall improvement in fretting performance had decreased. At 50/spl deg/C, the clad material lasted 3.2 times longer than the electroplated gold over palladium. The improvement in fretting performance by the clad material at 100/spl deg/C was slightly better and the clad material lasted 5.8 times longer than the gold over palladium material. At 200/spl deg/C, the clad material was only slightly better than the gold over palladium material system. If the number of cycles to failure at 200/spl deg/C is compared to the number of cycles to failure at 200/spl deg/C for both material systems, the increase in temperature caused a decrease in fretting performance. The average cycles to failure at 20/spl deg/C for the clad material was 1600000 cycles. At 200/spl deg/C, the clad material lasted for 72000 cycles. The electroplated gold over palladium material system lasted for an average of 189000 cycles at 20/spl deg/C and 64600 cycles at 200/spl deg/C. In general, over the entire temperature range, the clad material was a much better contact material.

Heat loss in insulated pipe the influence of thermal contact resistance: A case study

Abstract The thermal contact resistance is an important parameter in many heat loss problems. Determining the contact resistance for practical systems is quite complex due to the dependency of the relative geometry of the contacting surfaces. It is, therefore, difficult to make general contact resistance data available in the literature. In this paper, we first describe a simple model to predict the effect of contact resistance. This is followed by describing a simple device which can be used to measure thermal contact resistance for an insulated pipe system. The apparatus consists of a steel containment pipe exposed to saturated steam. The heat flux is determined by measuring steam condensate over a fixed period of time, while temperature measurements are obtained using standard type K thermocouples. The apparatus is calibrated using insulating materials with known thermal conductivities as they are necessary for the calibration and validation of the experimental setup. Once the device has been calibrated, the thermal contact resistance is determined for the insulating materials (standard fiberglass and calcium-silicate) using the electrical analog resistance method. It is shown also that the energy loss in a system may be affected by manipulating the contact resistance between the pipe and insulation. The effect of a small air gap to influence contact resistance is investigated. By placing spacers between the pipe and insulation, effectively producing a small air gap, we were able to significantly alter the contact resistance. A generalized optimization approach is also presented. The defined parameters are considered as a function of insulation cost and the cost due to the energy loss of the system.

Analysis And Characterization Of Electrically Conductive Adhesives

AbstractElectrically conductive adhesives (ECAs) are considered an alternative to solder interconnection in microelectronic circuit packaging. In an effort to understand the performance of this class of materials, several chemical analytical techniques have been employed to characterize polymer chemistry, filler morphology and surface chemistry. These techniques include fourier transform mass spectroscopy pyrolysis (FTMS), optical microscopy, confocal laser scanning microscopy (CLSM), scanning electron microscopy with energy dispersive x‐ray analysis (SEM/EDX), auger electron spectroscopy (AES) and photo‐electron spectroscopy (XPS). Samples studied were conductive adhesive layers and deposits, plated metal surfaces, cross‐sections of bonded joints and fractured bonds. Electrical contact resistance data were also taken on bonded joints. Three commercial adhesives were studied. It was found that thermal stability varied among the three adhesives with one adhesive showing degradation at as low as 200 °C. Differences were also noted in silver flake size, morphology and apparent contact area. Excellent contact resistance stability is achieved with two formulations on a palladium‐nickel alloy surface. In contrast, a hard gold surface yielded unstable contact resistance. Fractured bond surfaces were studied for both stable and unstable joints to understand mechanisms for contact resistance degradation. The increase in contact resistance is most likely caused by oxygen ingress along an interfacial bond where the adherend surface is smooth. The matrix polymer oxidized at the interface when exposed to temperatures above the glass transition temperature. Tin surfaces cause increasing contact resistance and nickel surfaces give an initial contact resistance that is more than two orders of magnitude higher than noble metal surfaces. Oxide formation in both cases is the likely cause for the unstable and high resistances. Various analytical techniques have been used to characterize and differentiate electrically conductive adhesives. Differences among three adhesives are noted and correlated to contact resistance performance.

Evaluation of Ti and TiN thicknesses for tungsten plug contact metallization

A statistical experimental design has been succesfully used to evaluate the integration of CVD tungsten plugs into a PVD-Ti/TiN/AlSiCu metallization. Optimum titanium (Ti) and titanium nitride (TiN) layer thicknesses for tungsten filled contacts with aspect ratios of up to 1.8 have been determined with respect to contact resistance and leakage current data in both n + and p + contacts. Ti thickness (10–50 nm), TiN thickness (50–150 nm) and contact depth (1050–1500 nm) were each varied in three levels and the corresponding responses were investigated for contacts with different diameter. The investigations show that for given contact dimensions, contact resistance is only determined by the Ti thickness. In order to achieve lowest contact resistances even in the contacts with highest aspect ratios, the nominal Ti thickness should at least be 40 nm. A deficiency in Ti, which causes higher contact resistivities, cannot be compensated by an increase of TiN thickness. These results are independent of contact doping. TiN thickness is the most relevant parameter with respect to barrier integrity. However, CVD tungsten filled contacts with a TiN barrier of nominally only 50 nm thickness exhibited lowest leakage currents and also did pass an electrical stress test (1000 h, 150°C, 1.9 × 10 6 A/cm 2), even if the aspect ratio was 1.8 TEM investigations are in agreement with these electrical data although they reveal that the effective barrier thickness is only approximately 10% of the nominal value in contacts with aspect ratio 1.4. Based on these results it is concluded that contact filling with CVD tungsten will be a viable and reliable metallization for sub-0.5-μm technology, especially if improved Ti- and TiN-deposition methods (like, e.g., collimated PVD or conformal CVD) are available.

A comparison of elastic and plastic contact models for the prediction of thermal contact conductance

Experimentally determined thermal contact resistance (conductance) data are compared with predictions based on two different theories. One of the theories assumes elastic contact, while the other theory is based on the assumption of plastic contact. Even though the high plastic index calculated for the contacting surface suggested that contacting asperities would deform plastically, the experimental data generally agree better with the predictions obtained using the elastic contact model than with the predictions obtained using the plastic contact model.

Experimental techniques for thermal contact resistance measurements

ABSTRACT A number of different experimental techniques have been used to determine the thermal resistance of materials in contact, depending upon specific test requirements. These techniques and associated experimental facilities are reviewed, including the traditional cut-bar vertical-column test facilities, and more specialized facilities and techniques for measurement of the thermal contact resistance of such configurations or contacts as bolted joints, periodically contacting surfaces, full and partial scale component models, and analog techniques. Experimental thermal contact resistance data are presented and compared for selected categories of materials in contact including similar metallic junctions, junctions with interstitial fluids or fillers, and metallic junctions with metallic and non-metallic surface coatings. These experimental results demonstrate that the characteristics of thermal contact resistance may be used to thermally enhance a junction between materials, or thermally isolate a junction, depending upon thermal design requirements.

Contact resistance measurements on p-type 6H-SiC

Specific contact resistance measurements are reported for Al-Ti ohmic contacts to epitaxial p-type 6H-SiC as a function of epitaxial doping. The circular transmission line method was used to measure the specific contact resistance including the sheet resistance of the epitaxial layer and the modified sheet resistance under the contact. Epitaxial layers with Al doping between 5.5×1015 and 2×1019 cm−3 yielded specific contact resistances between 2.9×10−2 and 1.5×10−5 Ω cm2. A good theoretical fit to the contact resistance data was obtained by assuming the metal-6H-SiC barrier height to equal 0.37 eV.

On the source of scatter in contact resistance data

Previous treatments have assumed that small fluctuations in contact window dimensions between devices are chiefly responsible for the scatter in contact resistance data. Although this is plausible, it is shown in this paper that the source of this scatter is variation in contact resistivity, ρc, from resistor to resistor. It is further suggested that ρc is Cauchy distributed. Since standard deviation is in theory infinite for a Cauchy distribution, very high values of resistance at a contact window would occur with much greater frequency than common sense might suggest.

Characterization of Rapid Thermally Nitrided Titanium Films Contacting Silicided and Non-Silicided Junctions

ABSTRACTIn the present work we have studied rapid thermally nitrided titanium films which contact self-aligned silicided titanium disilicide (TiSi2-salicided) and non-silicided junctions. We correlate electrical contact resistance data to SIMS results.

The Relationship Between Microstructure and Contact Resistance in NiAuGe/ZrB2/Au Ohmic Contacts to GaAs.

ABSTRACTThe microstructure and contact resistance of NiAuGe contacts to n-type GaAs were determined as a function of initial contact composition. The contact microstructures were found to contain varying amounts of of α, α’ and β (or Au7Ga2) Au-Ga, epitaxial Ge, NiGe and NiGeAs phases. A previously unidentified NiAsx (Zr,B) phase was also observed. The contact resistance was found to vary between 0.22-0.38±0.03Ωmm. Comparison of the microstructural and contact resistance data revealed that the ohmic formation models based on (i) the formation of a recrystallised n+ GaAs layer and (ii) the presence of a graded Ge/GaAs heterojunction were not applicable to this contact system.

Current crowding and misalignment effects as sources of error in contact resistivity measurements—Part II: Experimental results and computer simulation of self-aligned test structures

In this work we show that an accurate and straightforward extraction of the contact resistivity from contact resistance data can be achieved using properly designed self-aligned test patterns. In this way, the parasitic effects are minimized and the contact resistivity can be derived using simple one-dimensional models as confirmed by our computer simulation. Experimental results obtained in self-aligned structures are presented for Al/CoSi <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> /n <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> Si and Al-Si/n <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> Si contacts.

Current crowding and misalignment effects as sources of error in contact resistivity measurements—Part I: Computer simulation of conventional CER and CKR structures

In this paper we have investigated current crowding and misalignment effects as sources of error in the extraction of the contact resistivity from contact resistance data. Computer simulations have been carried out to analyze both conventional CER and CKR structures. The extent of the errors related to such parasitic effects is discussed, with particular emphasis on the effect of current crowding in misaligned contacts, in the case where the contact geometry is not correctly taken into account.

On the optimization of VLSI contacts

The contact-resistance characteristic of silicon devices has been a subject of research and development since the early days of silicon integrated-circuit technology. The contact-chain losses suffered by very large scale integration (VLSI), however, have made the minimization of contact resistance a critical parameter due to the large number of contacts per circuit and due to the increase of contact resistance with decreasing contact size. This paper will present a brief review of the theory of contact resistance, the literature, measurement techniques, and of the transmission-line model (TLM) for analyzing contact-resistance data. Contact-resistance data pertaining to shallow high-conductivity contacts for VLSI will be presented as a function of the junction parameters (implant dose, etc.) and of the contact area for BF 2 and arsenic implants with aluminum-silicon metallization. Contact-resistance data for a sputtered molybdenum silicide contact barrier for boron and arsenic implants versus contact area will also be presented and compared to the aluminum-silicon control samples with a discussion regarding the uniformity of contacts to silicon.

Solar cell contact resistance—A review

An overview of ohmic contacts on solar cells is presented. The fundamentals of metal-semiconductor contacts are reviewed, including the Schottky approach, Fermi level pinning by surface states, and the mechanisms of thermionic emission, thermionic/field emission, and tunneling for current transport. The concept of contact resistance is developed and contact resistance data for several different contact materials on both silicon and gallium arsenide over a range of doping densities are summarized. Finally, the requirements imposed by solar cells on contact resistance are detailed.

Contact Resistance on Surfaces with Nonuniform Contaminant Films

A probe has been designed for making point-by-point mapping measurements of contact resistance over large surface areas. The probe, which operates in the low force range of 5 mg to 5 g, permits simultaneous measurement of both contact resistance as a function of load and the integral of contact resistance versus force. To accomplish this a magnetically damped torsion bar mounted pendulum/sample holder is electromagnetically driven against a smooth spherical probe tip mounted directly on a force transducer which, in turn, is mounted on an x-y precision translation stage. The associated instrument package includes a variable sweep rate electromagnetic drive, high-frequency rejecting load and contact voltage amplifiers (the latter being an ultrastable differential amplifier), a voltage-to-frequency converter, a scaler, and an x-y recorder. The probe has been used to explore spatial variations in contact resistance due to a nonuniform fiuoropolymer film on a gold substrate. The data show a large statistical variability, which is simply analyzed by assuming normally distributed surface asperities and applying this assumption to the accepted model for multi-asperity electrical contact. This procedure leads to a prediction that the square of the conductance will follow a Gaussian distribution. Contact resistances that were obtained in the course of this work as a function of force are shown to be consistent with the multi-asperity model, Data are presented which agree well with the statistical model. This insight into the statistical variability of contact resistance data is useful in that it suggests a successful data smoothing technique that presents a reasonable appearing line map of the effective contact resistance due to a nonuniform film. It is demonstrated that data smoothed in this fashion can be favorably compared to the degree of surface contamination as determined with a scanning electron microscope.

Reliability of Clad Metal Inlays for Electrical Connectors

Following the prior publication [ 1 ], we tested more connector hardware of clad metal inlays the quality of which is quite close to the production level. In other words, the spring base material was all made of beryllium copper fully heat-treated after forming. The springs were punched and formed with a production the spring gaps were more uniform and all within the specified range, though in the high end. The inlay materials used in this extended test were: a) 18K Au (75Au25Ag), b) pure palladium (100 Pd), c) Alloy 69Au25Ag6Pt, d) 60Pd40Ag alloy, and e) alloy-55(55Au39Ag3Cd31n). These materials were reported to have relatively better performance among the many candidates we initially studied. The sample size used in these tests was much larger than the previous one; as a result, the experimental data are more reliable and meaningful. Two groups of connector hardware representing today's highdensity miniature electronic packaging were used. One group was the cylinder-cylinder contact, the other was the cylinder-flat contact. Also some discussion was devoted to the dimple-flat contact system. The contact-resistance data were collected over a period of 6 months to 1 year from three kinds of environmental tests. Both porosity and formability were acceptable for all the inlay springs. No wear-through contacts were found after 50 insertions with lubricant applied on the Au or Pd plated pins. All five inlay materials tested behaved almost equally well in their contact-resistance measurements. Previously the 69Au25Ag6Pt was chosen as the best, and the palladium stood as the second best at that time. However, in this paper we have shown that the Pd is clearly the winner in many aspects of the tests. The 69Au25Ag6Pt is equivalent to the 75Au25Ag alloy as the second best choice.