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Machine design and electrical contacts involve frequently elastic circular contacts subjected to normal loads. Depending on geometry, these may be Hertzian or surface contacts. Both possess highly nonuniform pressure distributions which diminish contact load carrying capacity. The achievement of a uniform pressure distribution would be ideal to improve the situation, but this violates stress continuity. Instead, the generation of a uniform pressure over most of contact area can be sought. Generally, equivalent punch profile which generates this pressure is found by numerical evaluation of double integrals. This paper simplifies the derivation of punch profile by using an existing correspondence between a polynomial punch surface and elastically generated pressure. First, an improved pressure profile is proposed seeking to avoid high Huber-Mises-Hencky stresses near contact surface. Then, this is approximated by the product between typical Hertz square root and an even polynomial, which yields directly the punch profile. Formulas for normal approach and central pressure are derived. [DOI: 10.1115/1.2197522] Keywords: circular elastic contact, contact improvement, improved contact pressure, Huber-Mises-Hencky stress

It has been shown that titanium disilicide is an appropriate material for producing contacts for electrical characterization of chemically altered silicon surfaces and nanostructures produced by ultrahigh vacuum or wet chemical techniques. The TiSi2/Si system can be flash cleaned at temperatures of up to 1200 deg C because of low diffusivity of the TiSi2.

Research into the design of silicon-on-insulator complementary metal-oxide semiconductor field effect transistors is presented. The fabrication of transistors using selective tungsten CVD processes is described.

Research is presented concerning the development of a small area contact on a ground plane of YBa2Cu3O7-y which was grown by Liquid Phase Epitaxy. The ramped edge structure of the contact is discussed.

A unified simulation of Schottky and ohmic contacts has been achieved. The model includes thermionic emission at the metal-semiconductor interface and distributed tunneling calculated at each grid of semiconductor around the interface. Rectifying characteristics of Schottky barrier diodes (SBDs) and contact resistances with high immunity concentration conditions are reasonable vs measurements. The contact resistance influence on MOSFETs with salicide and with source-drain extension and the immunity of Schottky barrier tunnel transistors from the short-channel effect can be seen.

Research was conducted to examine the increase in static friction force as the duration of stationary contact increases. A comprehensive kinetic meniscus model was developed to explain the phenomenon both for multiple asperity and single asperity contacts at a liquid mediated interface. Results reveal that the static friction increases up to a certain equilibrium time after which it remains constant.

Research was conducted to achieve a low specific contact resistance to p-type GaN by developing a contact. A bi-layer Ni/Au film deposited on p-type Ga followed by heat treatment in air to transform the metallic Ni into NiO along with an amorphous Ni-Ga-O phase and large Au grains comprised the contact. A model was used to explain the mechanism for obtaining low-resistance ohmic contacts for the oxidized Ni/Au films using energy band diagrams of the Au/pp-NiO/p-GaN structure.

A lateral switching relay structure has been developed which provides a double gold contact with as low as 70-m[Omega] measured contact resistance, 0.45-A current-carrying ability at MEMS compatible force levels, TTL compatible actuation, and air gap isolation when open. The die area used for the relay mechanism itself (distinct from the actuation) is approximately 75 [[micro]meter] by 100 [[micro]meter] and was designed to allow fabrication of the relays in the MCNC MUMP's dual polysilicon foundry process with no assembly. Design analysis shows that substantial characterization is needed to design optimal microrelays. Temperature softening and failure modes have been characterized by current voltage techniques. Polysilicon vernier structures were used to develop force/current/conductance curves. Relays using thermal actuators have been built. Index Terms - Contact physics, microrelay, plastic deformation, relay, tribology.

Research was conducted to examine the mechanical and electrical characteristics of full-size ITER multistrand Nb3Sn cable-in-conduit conductor samples under transverse, mechanical loading. The transverse magnetic force that takes place when the conductors are used in a coil was simulated. A summary of findings derived with up to several tens of full loading cycles are presented.

A study was conducted to investigate the feasibility of preparing low dielectric constant materials using a conventional, parallel plate, plasma enhanced chemical vapor deposition (PECVD) process and processing the film at 400 degrees centigrade. The SiC-based films investigated in the experiment were deposited in a parallel-plate radio frequency PECVD reactor. Experimental methodology, results and conclusions are discussed.

The reliability of and prevention of nucleation and growth of voids in interconnects in microelectronic circuits has become a major concern for the microelectronics industry. Diffusion is believed to have an important part in the nucleation and growth of voids in interconnects. A parametric study was therefore conducted to investigate in detail of void migration and evolution in an idealized interconnect due to electromigration induced surface diffusion. Results are discussed.

The formation of low resistivity palladium-based ohmic contacts to p-type 4H-SiC below 750 degrees Celsius was investigated. To this end, the electrical properties of the contacts were analyzed using I-V measurements and the transmission-line model technique. In addition, the thermal reliability and stability of the palladium contacts were evaluated by aging and temperature dependence electrical tests. The contacts proved stable at prolonged heating at a constant temperature of 500 degrees Celsius, which was not the case for contacts formed at lower temperatures of 600 degrees Celsius or 650 degrees Celsius.

The electrical properties of titanium silicide contacts to nitrogen implanted 6H-SiC were studied by applying linear transmission line technique structures at temperatures up to 673 K. Nitrogen was implanted into a p-type 6H-SiC epilayer at 500 deg C and activated at 1700 deg C, resulting in an activated donor concentration of N(sub D) = 5 X 10(super 9) cm(super -3) to a depth of 300 nm with a decreased electrically active surface concentration of about N(sub D) approximately = 5 X 10(super 18) cm(super -3).

A study was conducted to analyze the ageing of aluminum electrical contacts to porous silicon. Electrochemical etching was utilized to form the porous silicon layers under different conditions. The backsides of the wafers were coated with an aluminum layer and were annealed at 400 degrees C. Experimental results indicated that the chemical etching of the surface of the porous silicon correlated with the low diminution of the current.

The conductivity of thin wires depends heavily on the properties, particularly the geometry, of contacts. Three hypothetical cases of thin wires, which possess a radius less than the bulk screening length, are studied to show that the current-voltage characteristic of a wire differs in all cases and depends on the type of contacts, which can be the Ohmic or Schottky type. Wire conductivity increases with signal frequencies for any type of low-dimensional contacts.

A study presents direct experimental evidence demonstrating variations of the electrical energy storage across current carrying metal contacts as a result of additional gas concentrations in the working environment around the interface. Experimental results illustrate convincingly for the first time that the interfacial electrical energy of current carrying contacts may be modulated by the available ion concentration and the environmental pressure or air composition.

The emergence of the advanced composite industry and the need for low cost, highly reliable electrical/electronic devices has led to the potential of carbon fiber contacts made from conducive plastics to add value to select applications. A study was conducted to investigate fundamental contact behaviors of carbon fiber-based distributed filament contacts and, by comparing these behaviors with those of metals, to develop the foundation of a guideline for future applications of distributed filament contacts and create a basis for future research.

A study relating to research on the impact of arc energy on contact erosion in air for make and break operations presents a detailed description of a computer model which describes the manner in which the inherent synchronicity of the the electromagnet dropout time can cause unequal pole-to-pole contact erosion during three-phase AC-4 life testing. How this synchronous behavior can occur in an actual device is also discussed.

The internal electric field regions near implanted contacts on semi-insulating GaAs diode structures are highly nonuniform and localized. This was found in the imaging of these regions using electron beam induced current (EBIC) in a scanning electron microscope. The contact-related fields were found to be able to dominate the entire region for small intercontact distances. EBIC imaging is found to provide a good estimate of the field distributions in trap-dominated high-resistivity materials.

Experiments were conducted to describe the impact of stearic acid on the frictional and contact resistance properties of aluminum-aluminum sliding interfaces. The reactivity of stearic acid with the aluminum metal was analyzed. Oxide formation in the contact interface was observed and caused an increase in contact resistance. The findings suggest that stearic acid is an excellent lubricant for aluminum interfaces but not for aluminum-aluminum electrical contacts.

Contact electrification measurements were performed on micrometer-sized spheres composed of polystyrene and flat substrates of either freshly cleaved, highly oriented pyrolytic graphite (HOPG) or a 0.2-micron-thick Au(111) film grown on mica. Atomic force microscopy was employed. The polystyrene/HOPG interaction showed substantial electrostatic charging relative to the polystyrene/Au system.

Ohmic contacts on p-type GaN films were developed using Ni/Au layers prepared by thermal alloying and electron beam evaporation. The presence of Ga-Ni and Ga-Au compounds at the metal-semiconductor interface was found to cause a decrease in Schottky barrier height. X-ray diffraction measurements also reveal that Ni3N and Ga4Ni3 compounds developed at the metal-semiconductor interface.

An atomic force microscope with a conducting probe was employed in the examination of localized electrical resistance in metal surfaces. The approach enables the generation of local conductance and surface roughness in nanometer scale resolution. Results show variations in local resistance values of different orders of magnitude between two adjacent grains. The measurements may also be employed in determining the mechanical properties of the tip/surface noncontact.

A two-dimensional optical arrangement was employed in examining arc mobility in three Ag/SnO2 contacts and in an eroded Ag/CdO contacts in a model switch. Contact gap arc commutation was found to cause the high apparent mobility in two Ag/SnO2 materials. Arc commutation and arc creeping were observed in Ag/CdO and Ag/SnO2. No correlation was observed in the level of contact erosion and apparent arc mobility.

A test system was proposed for examining short circuit arcs associated with miniature circuit breakers operating in an alternating current supply of 240 volts. Arc root motion under short circuit current of up to 6 kA was determined through an optical fiber imaging system. Results show that the cathode root motion dominates the variation of peak current level and arc runner materials.

A model was proposed for arcing electrical contact energy transport. The model considers the loss of vaporized material and relates this loss to the contact's received energy. Arc energy was determined by dividing the arc into the cathode falls, plasma and anode regions. Calculations of radial and channeling energy transport processes were verified using experimental data at 9 A, 64 V DC.

A study was conducted on PdI-447 nm and PdI-540 m, spectral intensity and temperature distributions in a Pd arc column cross section near the cathode contact in circuits of DC 50 V/3.3-5.0 A. Total measured spectral intensities was found to decrease in a short arc while radial temperature distributions were found to be constant. The dependence of arc temperatures and spectral intensities indicate that contact metal vapor density was high at the start of a breaking arc and that arc duration was long when metal-vapor quantity was high.

A devise is proposed for measuring gold electrical contact adhesive force. The electrical contact examined is installed on a small electromagnetic relay cantilever supporting arm. The apparatus provided measurements of contact and adhesive force with errors of less than 1%. The device, however, was found to be affected by contact force and sliding motion number and amplitude while measuring adhesive force.

A study was conducted on the microstructural reactions of PdGe ohmic contact to n-type GaAs using x-ray diffraction, slow positron beam and Auger electron spectroscopy. The lowest contact resistance of 1.7 ohm mm and the formation of a PdGe compound were found at the annealing temperature of 240 degrees C. Moreover, Ga vacancies were formed below PdGe during the formation of PdGe ohmic contact to n-type GaAs.

Stable low resistance contacts to TlBaCaCuO thin films utilizing trilayer and single layer metal contacts were developed. Shadow/photoresist masks were used to evaporate Au contacts on patterned and unpatterned contact pads for single layer contacts. Large contacts exhibited the optimum contact resistivity at 1.4x10(super -8) ohm cm2 at 78 K. Contact resistivity values were not altered despite several thermal cycling processes.

Studies were conducted on a current-biased Nb-(constrictions)-NbN (S-c-S') contacts to demonstrate that its low-frequency voltage noise properties have been described by current mesoscopic two-terminal conductor theories. The theory based on the single Andreev reflection model without heating was used to analyze the quasiparticle characteristics of the contacts. Results reveal that there is no significant excess noise contribution related with the Andreev reflection.

The quantitative characteristics of stationary electric contacts in electrical apparatus have been given by means of some calculations, based on an artificial model of the current flow lines which highly simplifies the treatment. We have developed a 3-D finite element method by which the static characteristics of the electric contacts having asymmetric shapes can be analyzed. Repulsion forces in the stationary electric contacts with rectangular solid contact members as well as ones with cylindrical contact members are calculated by our method. The validity is confirmed by comparing with the results by the well-known Holm formula[1].

Thermally stable, low-resistance ohmic contacts to GaAs were produced by utilizing PdIn metallization sputter-deposited from an alloy target. Average specific contact resistances (rho(sub c)) in the 10(super -6) ohm-sq.cm. range were attained upon annealing at 600 degrees C or higher. Contacts annealed under the optimum condition of 850 degrees C for 15 sec. showed an average rho(sub c) of 2.5 X 10(super -6) ohm-sq.cm. The 100 hours of thermal aging at 400 or 500 degrees C increased their average rho(sub c) to 3.0 X 10(super -6) and 1.0 X 10(super -5) ohm-sq.cm., respectively.

Phase formation in rapid thermally annealed Pd/Ge contacts on In0.53Ga0.47As was examined through cross-sectional transmission electron microscopy, convergent-beam electron diffraction and energy-dispersive x-ray analysis. Solid-phase regrowth occurred in the same way as in Pd/Ge contacts on GaAs or InP. The reaction began at low temperatures with the formation of an amorphous Pd-In-Ga-As layer, which crystallized at higher temperatures producing hexagonal Pd4In0.53Ga0.47As. Above 250 degrees C, this phase decomposed due to epitaxial solid-phase regrowth of In0.53Ga0.47As and formation of Pd-Ge phases. The stable composition was attained at temperatures beyond 350 degrees C.

Interfacial microstructures of Pd/Ge/Ti/Au ohmic contact to n-type GaAs were studied utilizing cross-sectional transmission electron microscopy and the results are employed for interpreting the electrical characteristics. Annealing at 300 degrees C produces a contact resistance of 0.62 ohm mm and the layer structure is modified to GaAs/PdGe/Au4ti/TiO. The ohmic contact is formed through a solid phase regrowth of GaAs heavily doped with Ge below the PdGe layer. The lowest contact resistance of 0.43 ohm mm was measured at 380 degrees C. The layer structure is modified to GaAs/(Ge-Ti)/PdGe/TiO.

A mathematical model of voltage and temperature characteristics during contact opening is constructed. It characterizes several stages of heat transfer, namely, contact separation, contact melting, evolution and rupture of liquid metal bridge, electric arc ignition, spreading of arc in the bridge metallic vapors and conversion of the metallic arc phase into the gaseous state. In addition, it shows that the arc evolves in either a transient or diffusive manner after bridge rupture.

The use of barrier coatings and chromating treatments to minimize corrosion of porous noble metal plated contacts was considered. Specifically, the performance of test contacts consisting of a nickel underplate plated with either gold or gold flashed palladium and coated with a polyphenylether-microcrystalline (PPE-MCW) wax mixture was investigated under corrosive and highly humid conditions. The results proved showed that the oil-wax PPE-MCW barrier coating decreased pore corrosion.

The occurrence of arc-cathode erosion in pure tungsten and two-percent-thoriated tungsten cathodes was investigated. Specifically, measurements of cathode temperature distribution as well as observations of cathode spot behavior and cathode metallurgy after arcing were obtained using different plasma gases and cathode geometries. The results demonstrated that cathodes should be designed to avoid overcooling which leads to steep temperature gradients and ion bombardment.

The performance of a 6H-SiC buried-gate n-channel depletion-mode junction field effect transistors at temperatures of 25-350 degrees Celsius was modeled in terms of their dc characteristics and noise spectral density. The 6H-SiC active components, which was designed and fabricated for use in a temperature sensor, demonstrated high sensitivity, excellent linearity and stable operation from -50-500 degrees Celsius.

Bounds on the potential capabilities of metal fiber brushes with respect to speed, current density and losses are examined. Specifically, it is shown that metal fiber brushes are good replacements monolithic graphite brushes especially in electrical transportation projects. To facilitate their widespread use, several issues such as open air operation, cost, packaging, installation and wear performance must be addressed.

The electrical performance of (Ba,Pb,La)TiO3 ceramics doped with different additives and exhibiting a positive temperature coefficient of resistance (PTCR) behavior was investigated. Specifically, three PTCR equations based on the Heywang-Jonker model were used to correlate measurements and calculations of resistivity. The good agreement was attributed to the assumption that different additives lead to different surface states such as cation vacancies, acceptor impurities and interface states from oxygen adsorption are found at the grain boundary.

The arc erosion process in low-voltage Ag/CdO and Ag/SnO2 contactors was investigated under dc conditions at a current range of one amperes to 16 A. The results showed that arc erosion proceeds through three stages, namely, metallic ion, evaporation and liquid removal. Likewise, it was found that both contact materials exhibited similar behavior at currents of one to four amperes and 64 V. Their performance differed at currents between four amperes to 16 A.

The contact erosion occurring in motor contactors stressed according to IEC H947-4 AC3 duty was investigated via make-only, break-only and make-and-break erosion tests on Ag/CdO and Ag/SnO2 contacts and a model switch. The results proved that contact erosion is a function of the interaction between thermal and mechanical stresses. Due to this, it is best to apply make-and-break operations even if erosion is of the make-only or break-only type.

A new approach to minimize contact bounce in an electric contactor is introduced. It exploits power electronics, namely, timing coil energization periods, to control the field flux in the armature coil of a moving contact and decrease its kinetic energy. According to scanning electron microscope photographs of its implementation in a GEC Ltd. 415-V contactor and in a test rig, controlled coils have reduced bounce and less contact erosion.