Showing papers on "Contact resistance published in 1978"

Studies on electrical conductivity of insulator‐conductor composites

Abstract: The variation of electrical resistivity of an insulator‐conductor composite, namely, wax‐graphite composite, with parameters such as volume fraction, grain size, and temperature has been studied. A model is proposed to explain the observed variations, which assumes that the texture of the composite consists of insulator granules coated with conducting particles. The resistivity of these materials is controlled mainly by the contact resistance between the conducting particles and the number of contacts each particle has with its neighbors. The variation of resistivity with temperature has also been explained with the help of this model and it is attributed to the change in contact area.

Nonalloyed Ohmic contacts to n‐GaAs by molecular beam epitaxy

Abstract: We report the formation of Ohmic contacts to n‐GaAs without the need for a high‐temperature alloy. Heavily doped n‐GaAs(Sn) was grown using molecular beam epitaxy in which the concentration of free carriers was as high as ‖ND−NA‖=6×1019 cm−3 yielding specific contact resistance rc=1.86×10−6 Ω‐cm2.

Contact problems involving a cooled punch

Abstract: Certain problems in which a cooled rigid punch indents an elastic half-space have no steady state solution. A simple model is described in which it is shown that this paradox is avoided by the assumption of a thermal resistance varying inversely with contact pressure. A limiting case of this system retains linearity and introduces a state of “imperfect” contact in which contact pressure is negligible but there is significant thermal contact resistance.

Ohmic contacts produced by laser‐annealing Te‐implanted GaAs

Abstract: We report the formation of Ohmic contacts to high‐dose (∼1016 cm−2) Te‐implanted n‐type GaAs annealed with a Q‐switched Nd : YAG laser. The annealing results in a Te concentration greater than 10 times the equilibrium solubility and the formation of free Ga at the surface. Ohmic contacts of specific contact resistance rc≃2×10−5 Ω cm2 were obtained by first removing the surface Ga by an HCl etch and then backsputtering to remove 50 A of GaAs, thereby exposing a surface of high Te concentration.

The Lubrication of Electrical Contacts

Abstract: The objectives of lubricant compounding for industrial uses involving the possibility of metallic contact, and those of lubricant compounding for electrical contacts are almost mutually exclusive. In the former case surfaces must be separated and in the latter, metallic contact must be maintained. The modern principles of lubrication are therefore simply explained and those which may be applicable to electrical contacts in field field of boundary lubrication are stressed. Types of contacts are then defined and the appropriate lubricant properties applicable to each type are discussed; some (like creep, prevention of oxide formation, and resistance to arcing) in more detail than others. Methods of application are discussed. The aim is to suggest directions for much needed research in the lubrication of electrical contacts.

Pressure-sensitive resistors

Abstract: The pressure-sensitive resistor comprising an electroconductive elastomer, in which an electroconductive particulate material is dispersed, two electrodes placed on the opposing surfaces of the elastomer, a means for providing a compressive force between the electrodes and a means for adjusting the compressive force, works on a novel principle that the elastomer composite exhibits a positive coefficient in the curve of compression vs. resistance relationship when the compressive force is varied in a region exceeding an inversion point at which the resistance of the elastomer as measured in the direction of compression is minimal. The coefficient in this positive region is smaller than in the ordinary negative region, so that the variable resistance of the resistor can be controlled very delicately together with the decreased contribution of the uncontrollable contact resistance.

An exact derivation of contact resistance to planar devices

Abstract: A mixed boundary-value problem is formulated for an imperfect rectangular contact to a semiconducting sheet (layer). An exact model for derivation of contact resistance is developed and its solution by conformal mapping and eigenfunction expansion is presented. The expression for contact resistance is similar to that for a perfect (lossless) contact but includes an additional term containing the lowest-order coefficient in the infinite series expansion of the complex potential function. The calculated contact resistances are compared with those obtained from three approximate models: lossless contact, transmission line, and extended transmission line models. The extended transmission line model appears to be a very satisfactory approximation provided the ratio of contact length to sheet thickness is no less than 0.5.

The Behavior of Surface Oxide Film on Ruthenium and Rhodium Plated Contacts

Abstract: Although a surface oxide film on platinum-metal contacts is effective in preventing these contacts from polymerizing organic materials, it causes an increase in contact resistance. It is important to determine the thickness of surface oxide film which effectly prevents organic polymerization without causing a significant increase in contact resistance. Auger Electron Spectroscopy is used here to determine the thicknesses of the surface oxide films formed on Ru and Rh plated contacts at various temperatures in synthetic air. These are compared with results for untreated Ru and plated Rh contacts. Contact voltage versus contact resistance and contact force versus contact resistance characteristics of plated Ru and Ru oxidized after plating are measured by the crossed-rod method to study the relationship between contact resistance and thickness of a surface oxide film. The extent of organic polymerization on Ru and Rh plated contacts is determined by operating the contacts unloaded (dry) and monitoring the contact resistance after the treated and untreated contacts are exposed to benzene vapor. !t is found that, when the surface of the contacts is covered by a thin oxide film in either the case of plated Ru or plated Rh, the contact resistance can be low and stable, whereas contacts cleaned by Ar+ bombardment prior to sealing will be high in resistance. From these experimental results, it is determined that the thickness range of surface oxide film which prevents polymerizing without any measurable increase in contact resistance is approximately 5A ~25A.

Effects of contact metals on minority carrier diffusion lengths in GaAs

Abstract: Contact technology for GaAs involves optimizing such factors as contact resistance or Schottky barrier height, alloy cycle conditions, thermal ageing, adhesion, and ease of high resolution processing. Minority carrier properties may be significantly degraded by in-diffusing contact metals. At typical alloying conditions of 10 sec at 500° C, Ni diffuses at least 10 μm and reduces the hole diffusion length (Lp) in vapor phase epitaxial GaAs from 4.4 to 1.7 ym. At 600°C, Lp becomes 1.0 μm. Other metals, such as Fe, Pt, and Cr, significantly improve Lp in VPE GaAs. Lp increases from 3.0 to 5.0 μm for an Fe diffusion of 5 minutes at 500°C. These improvements may be due to interaction of in-diffused Fe with recombination centers, such as Ga vacancy complexes or Ni. Fe causes increases in minority carrier diffusion lengths also in n and p type ingot GaAs, though 800 – 900°C diffusions are required and at these temperatures the doping is significantly changed by Fe acceptors.

A high‐efficiency GaAlAs double‐heterostructure photovoltaic detector

Abstract: An antireflection‐coated GaAlAs double‐heterostructure photovoltaic detector is described whose extrinsic power conversion efficiency is 56% when used with a focused 8075‐μm wavelength laser beam. This, to our knowledge, is the highest photovoltaic efficiency yet reported. A partially reflective rear contact provides extrinsic quantum efficiencies exceeding 0.90 with a relatively thin active region. By restricting the diameter of this contact to 50 μm and using high dopings to reduce series resistance, open‐circuit voltages of 1.15 V and fill factors up to 0.84 are obtained. The series resistance was 3.0 Ω, with 1.0 Ω being attributable to the contacts.

Apparatus for measuring semiconductor device resistance

Abstract: A test structure for enabling the accurate measurement of the resistance characteristics of a semiconductor material, of the type which includes one or more pairs of electrical terminals disposed on the surface of the material to enable measurements of the resistance encountered by currents passed between the terminals. A pair of terminals includes a first terminal extending in a closed path, such as a circle, around a second terminal, so that all currents flowing between the terminals flows along a region of known width and length. Two or more pairs of concentric terminals can be utilized, wherein the ratio of radii of each pair of terminals is the same as the ratio for all other pairs of terminals, to facilitate the calculation of the contact resistance between each terminal and the semiconductor surface, as well as the calculation of the resistance of the semiconductor material apart from the effect of the terminal-to-semiconductor contact resistances.

New contact resistance profiling method for the assessment of III--V alloy multilayer structures

Abstract: A practical technique for the assessment of multilayer III–V structures is described which is based on the measurement of the contact resistance between a tungsten carbide probe and an angle lapped sample surface. The technique has been applied to homostructure and double heterostructure layers of GaAs, GaAlAs, InP and GaInAsP and quantitative information on the doping profiles has been obtained by calibration against binary material samples of known impurity levels.

Contact Resistance Characteristics at Low Temperature

Abstract: The application of cryogenics to the fields of electrical engineering has great possibility. However, performance of contacts used in the application may be estimated to deteriorate due to contaminant films. It is important subject to clarify the electrical conduction mechanisms of contacts covered with contamination films to obtain low contact resistance characteristics at the low temperature as well as at the normal temperature. From these standpoints, electrical conduction mechanism and contact resistance at low temperature were examined. Schottky current was observed in oxide film covered contacts over a range from 300 K to 77 K. The contact resistance at the low temperature increased by approximately 100 times or more over that of normal temperature due to Schottky conduction. For clean surface, the contact resistance passes through a minimum at low temperature due to thermal contraction of true contact area. In conclusion, Schottky conduction was found predominantly. Therefore, if the contaminant films exist at the contact surface, contact resistance increased remarkably at low temperature. Moreover, even for contacts of clean surfaces, contact resistance has a limiting value unlike resistance of metal conductors. These results give a serious problems in the performance of contacts for the cryogenic application.

A two dimensional analysis of sheet resistance and contact resistance effects in solar cells

Abstract: A computer model is developed to study the two-dimensional nature of the sheet resistance and contact resistance effects in solar cells. A major result is the demonstration that the distributed nature of the semiconductor sheet resistance causes the terminal dark I-V characteristics to exhibit an exp(qV/2kT) type dependence even when the one-dimensional characteristics of the cell exhibit an exp(qV/kT) type voltage dependence. The analytical model which is developed provides an easy method for estimating the sheet resistance of a solar cell from the terminal I-V data.

Sputtered Ruthenium as a Contact Material for Sealed Reeds

Abstract: Cobalt-hardened gold is used as a contact material on remreed sealed contacts. A possible change of material for contacts of this type has been studied. The contact material investigated consists of a thin film of ruthenium over a thicker film of hardened gold. Both films are deposited by dc sputtering. The advantages of this contact finish compared to electroplated hard gold are reviewed: lower erosion per arcing operation, reduced arcing, and better resistance stability due to lower foreign element comtamination. The reliability of ruthenium contacts is related to that of hard gold contacts. A small change of contact geometry (gap and overlap) is needed to maintain the contact resistance at the level found with hard gold. The reliability is better in low-voltage (~5 V) level operation, due to the elimination of carbonaceous contaminants. The ruthenium contacts exhibit longer life in erosion tests involving cable discharges. Ruthenium contacts can be sealed off in a water free atmosphere so they could be used at below-freezing temperatures. Ruthenium contacts are able to withstand magnetostrictive scrubbing without sticking failures. However, the life of the ruthenium contact when switching current of 100mA (make and break) at 50V in a resistive load does not show significant improvement over hard gold. This is explained in terms of bridge transfer due to chattering during the make operation of the contacts.

AG-Metal oxides electrical contact materials containing internally oxidized indium oxides and/or tin oxides

Abstract: An electrical contact material obtained through internally oxidizing a silver alloy which is the solid solution with 3 to 11 weight percent of tin and other solute metal element(s). The alloy material is improved of its contact resistance by diffusing into the silver matrix 0.1 to 5 weight percent of metals having a decomposition and sublimation temperature lower than the melting point of silver and then by internally oxidizing the material.

A Field Study of the Electrical Performance of Separable Connectors

Abstract: A three-year study of separable electronic connectors in operating telephone equipment was conducted to determine failure mechanisms and rates of presently used designs. The study of nine different connector types (six of which are reported) was carried out in four cities, and higher than expected contact resistances were observed. These were due to factory contaimination and not pore corrosion as originally assumed. Nevertheless, there is some evidence to suggest that a time-dependent "wear-out" mechanism exists. Finally, disengagement/reengagement cycling does not offer an adequate "fix" for reducing high-contact resistance because the frequency of reducing contact resistance is about the same as the frequency of increasing contact resistance in some connector designs. The results are from the efforts of many people working as a team at four Bell Laboratories locations and are presented in order to bring together several important conclusions.

Surface Contaminant Characterization Using Potential-Current Curves

Abstract: Results are reported of an investigation of potentialcurrent curves for the characterization of contaminants on electrical contact surfaces. It was found that pronounced leveling of the potential (decreasing contact resistance) occurs as the junction temperature is raised through the melting temperature of the contaminants. Thus the characteristic shape of potential-current curves may be used to distinguish between low- and high-melting organic contaminants and between these and oxides or refractory particles. This in situ diagnostic test has found recent industrial application in the manufacture of sensitive switches and in troubleshooting switches after prolonged inactive storage in the field.

Theoretical Calculation of the Transient Temperature Rise and the Welding Limit Current of Point Contact Due to Momentary Current Flow

Abstract: Calculations of the transient temperature rise of point contacts with large contact areas were carried out using a hemisphere contact model. The results obtained are as follows. 1) The temperature \thetam at the contact surface is not a function of I/a (I is the current, a the real contact radius) as in the stationary contact theories, but is a function of a, I, and /'s frequency. 2) A relation between \thetam and contact voltage U shows hysterisis characteristics. 3) Transient calculation gives a higher welding limit current than the stationary theories, particularly for large real contact areas. 4) When taking into consideration the change of real contact area during current flow, the particular contact voltage wave forms and the relation between U and the contact resistance Rc, which have been observed experimentally, can be explained by the calculation.

Influence of a microwave field on the critical current of superconducting contacts

Abstract: An investigation is reported of the influence of nonequilibrium electrons on the critical current of a superconducting contact subjected to an external hf field. It is shown that the effective cooling of electrons trapped in the region of the contact which has a lower value of the gap may result in a considerable increase of the critical current. The maximum critical current is found and a study is made of the dependence of this current on the power at various temperatures. On approach of the critical temperature there should be a transition from stimulation to suppression of superconductivity in the contact, which agrees with the experimental results. The frequency limits of the existence of the effect are estimated.

Specific contact resistance of the Ni/AuGe/nGaP system

Abstract: This work studies the specific contact resistance for Ni/Au-Ge/nGaP system at the rectifying regime, i.e. for which the heat-treatment temperature is below 400°C and the I–V characteristics exhibit a rectifying behavior. The specific contact resistance is first computed by using the generalized majority carrier transport theory derived by Chang and Sze [1]. The computed theoretical results are then used to interpret the experimental data which are obtained by measuring the specific contact resistance, at zero bias, as a function of the temperature for as-deposited and heat-treated Ni/Au-Ge/nGaP Schottky diodes. Au/nGaP Schottky diodes are also fabricated to verify the theoretical results. It is found that the barrier height for the Ni/Au-Ge/nGaP system rises from the as-deposited value, 1.10±0.04 eV, to the value of the Ni/nGaP system, 1.27∓0.02 eV, as the contact is heat-treated at various temperatures up to 360°C, the eutectic point of the Au-Ge system, and drops rapidly as the contact is heat-treated above 360°C. The barrier height rise is believed to be caused by the Ni in-diffusion toward the Au-Ge/nGaP interface during the heat-treatment. The smaller temperature dependence of the specific contact resistance for Schottky diode samples heat-treated above 360°C indicates that after heat-treatment above this temperature, an n+ layer is formed on the GaP surface. The theoretically computed results are used to fit the experimentally measured data to obtain the effective n+ doping concentrations and barrier heights.

A comparative reliability study: Aluminum gate vs. gold-base gate GaAs MESFETs

Abstract: Temperature accelerated tests, with and without bias, show that the considerable MTTF advantage, at elevated temperature, of Al gate MESFETs over gold-base gate devices diminishes at lower temperatures. This is due to the difference in the activation energies, E A , of the respective gate metallization systems (E A = 0.8-1.2 ev for Al-gate and E A = 1.3-1.8 ev for gold-base gate devices). The standard deviation of the logarithms of the lifetimes, σ, was less than 0.3 in all cases. The primary mode of failure for all types of devices was a gradual degradation of I DSS . Impurity profiles indicated that the associated failure mechanism is a gate metal interaction with the epi-layer. It has been established that the degradation of the low-field resistance, R DS , is not an index of contact resistance degradation, but the logical consequence of the above failure mechanism.

Low temperature electroplated Au-SnNi-Au ohmic contacts on n type GaAs

Abstract: A method is described for fabricating ohmic contacts on n type GaAs by alloying electroplated layers of Au-SnNi-Au at 300°C, resulting in a contact resistance of approximately 3 x 10 -5 Ω cm 2 . In applications for which this resistance is adequate, the technique has the advantage of requiring low-temperature alloying for short times.

Contact fault detector

Abstract: A technique and a circuit is described for readily detecting contact resistance build-up and contact chatter Closed contacts are arranged in series with each other and with a resistor A voltage is applied across the series arrangement Each contact is shorted by jumper lead and/or separately jolted If the contact is defective, the voltage step or series of voltage pulses will appear at the junction between the resistor and the contacts in series The voltage step or pulses are coupled through a capacitor to a normally on switch which changes state to indicate the presence of the pulse indicating the defective contact A resistor coupled to the capacitor provides a differentiating circuit to bleed off any charge in the capacitor to permit sequentially testing each contact A further resistor in combination with the capacitor provides an integrating circuit to assure appropriate capacitor charging in response to the negative going pulses that occur when there is contact chatter

Behavior of Contact Surfaces Consisting of Gold Alloys in H 2 S-NO 2 -SO 2 Atmospheres

Abstract: Tests Carried out in connection with a project for ensuring suitable test atmospheres for precious-metal contacts are reported. The contact resistance behavior of Au alloys is described after exposure in a flowing atmosphere of cleaned air mixed with the aggressive gases H 2 S, NO 2 , and SO 2 at concentrations between 0.4 and 4.0 ppm. By means of a regression calculation the influences of the different gas components are determined. In addition to the electrical measurements the chemical compositions of the tarnish layers were analyzed by SIMS.

Electrode forming method for gallium phosphide light- emitting diode

Abstract: PURPOSE: To obtain a stable electrode with good reproducibility without failing to crystallize a Gap layer, by adding a thin group V element to the surface of the GaP layer when forming the electrode on the GaP layer constituting a light-emitting diode. CONSTITUTION: On N-type GaP substrate 11, P-type GaP layer 12 is formed by liquid-crystal epitaxial growth to constitute a red light emitting diode, and group V element ions such as As are injected into its surface to form thin As element injection region 14. In this way, several empty lattice points are made here, an electrode composed of Au-Be alloy 12a and Au layer 12b is fitted in this area, and an electrode of Au-si alloy layer 11a and Au layer 11b is adhered to the reverse surface of substrate 11. Then, a heat treatment is carried out in an Ar atmosphere of 500°C for about twenty minutes and the layer-11b side is mounted on header 15. Consequently, the light-emission efficiency increases by approximately 10% in comparison with an ordinary diode and the contact resistance of the electrodes decreases down to 5× 10 -5 Ωcm to the contrary. COPYRIGHT: (C)1979,JPO&Japio