Showing papers on "Contact resistance published in 1970"

Electron tunneling and contact resistance of metal-silicon contact barriers

Abstract: The contact resistance of Al and Pt on n -type Si over a wide range of doping concentrations (10 18 → 2 × 10 20 cm −3 ) has been measured at both room temperature and liquid nitrogen temperature. These experimental results are compared with theoretical calculations based on a model with electron tunneling through the potential barrier at the interface as the dominant mechanism of current flow. Good agreement is found. It is hoped that this physical model can be used as a guideline in developing ohmic contacts for various semiconductor devices.

Electrical properties of single carbon fibres

Abstract: A study has been made of the electrical resistance, the electrical noise and the change in resistance as a function of mechanical strain of single carbon fibres from seven different batches. The resistance of the fibres was found to be much larger than would be anticipated if they were entirely composed of aligned graphite crystallites and the electrical noise was found to have the characteristics of the contact noise associated with loose aggregates of carbon granules. Most fibres showed a linear increase in resistance above about 01% strain. Variable behaviour was observed in the initial strain region for all but a few fibres. In some cases fibres showed time dependent electrical properties while remaining mechanically stable. It is suggested that the electrical properties of the fibres are largely determined by the contact resistance between the fibrils which make up the fibres and the variation of this contact resistance with pressure. The possible electrical properties of a simple model of the fibres are discussed.

Process for making conductive polymers and resulting compositions

Abstract: Conductive polymer having a steeply-sloped positive temperature coefficient (PTC) of resistance is composed of crystalline polymer having a narrow molecular weight distribution and filled with conductive particles such as carbon black, tin powder, gold powder, silver powder and other conductive particles which do not oxidize at the temperatures to which the composition is subjected during processing. Additional additives are incorporated to impart desired characteristics. Stabilizing agents which prevent deterioration of the resistance characteristics of the material include alkylated polyhydroxy phenol and phenylbetanapthylamine. (Dialkylphenol-sulfide may be added to reduce degradation at a metal polymer interface thus reducing contact resistance). Flame retardants which do not deleteriously effect the resistance characteristics include phenylbetanapthylamine high chlorinated perchloropentacyclodecane and antimony oxide. The several ingredients are for a preliminary mixed together, then subjected to a more thorough mixing step to effect an adequate dispersion of the filler material throughout the polymer, and then subjected to shearing forces for a limited period of time while maintaining the mix within a desired temperature range. The mix is then formed in the desired configuration as by inserting into a preheated mold while still at an elevated temperature. The formed element is removed from the mold and machined preferably to a rough finish to facilitate bonding of electrically conductive coatings to spaced locations thereof. The element is then coated with electrically conductive coating and annealed to minimize contact resistance.

A rapid evaluation technique for functional Gunn diodes

Abstract: A rapid technique for estimating the carrier mobility, average and minimum carrier concentration, and contact resistance in operational Gunn diodes is presented. Although the physical nature of the functional Gunn-effect device (i.e., an n-type active layer with only two n+ohmic contacts) restricts what can be measured, it will be shown that information useful for estimating device performance can be obtained if some simplifying assumptions are granted. The procedure is illustrated by data obtained from five separate wafers of vapor-phase, epitaxially grown gallium arsenide.

Electrical Characteristics of Contacts Contaminated with Silver Sulfide Film

Abstract: Frequently the electrical performance of silver contacts is impaired by the unavoidable growth of a sulfide film on the mating contact surfaces. In the case where one or both of the electrodes are silver, or partly silver, and a silver sulfide film is formed on one or both of the electrodes, the electrical performance is greatly deteriorated and is among the most complex found on contaminated contacts. A recent study of the electrical performance of various sulfided contacts is reported that showed that they are characterized by an increased contact resistance that is dependent on the voltage polarity, by a nonohmic relationship between the contact voltage and current, and by a resistance that changes with time. A theory is proposed to account for the observations made with these contacts that is based on the semiconduction properties of silver sulfide, the high mobility of positive silver ions in silver sulfide, the tunnel effect, the widening of established conduction channels through the film by electrical forces (B fritting), and the crystal structure of silver sulfide, which can be found in either one of two forms depending on its temperature.

Ohmic Contacts to Silicon Carbide

Abstract: We have studied a number of metal alloys in a search for improved ohmic contacts to SiC. A Cu–Ti eutectic alloy wets SiC at 880°C forming a shallow contact which is ohmic on p‐type SiC. An Al–Si eutectic wets SiC at 900° to 1000°C giving a contact which is ohmic on p‐type SiC; the penetration is 300 to 500 A.

Positive contact resistance soldering unit

Abstract: A positive contact resistance soldering unit which has a relay therein, which is operated by a foot switch for selectively coupling a milliohmeter to the electrodes for measuring the resistance between the electrodes and the workpiece in order to determine the best contact therebetween. When the milliohmmeter indicates that the electrodes are in good contact with the workpiece the foot switch is depressed connecting the output of a power transformer to the electrodes to begin the soldering operation.

Correction terms for contacts to diffused resistors

Abstract: Correction terms obtained from measurements on typical planar resistors are given and compared to values expected from two different mechanisms: inhomogeneous current flow around the contact or contact resistance between metal and diffusion layer Good agreement between contact resistance model and experiment is shown

Metallic contact and interconnection system for semiconductor devices

Abstract: 1,262,544. Semi-conductor devices. TEXAS INSTRUMENTS Inc. 1 May, 1969 [10 May, 1968], No. 22234/69. Heading H1K. An ohmic contact to a zone of a semi-conductor device or integrated circuit comprises a layer of rhenium overlaid by a layer of high conductivity metal. The integrated circuit of Fig. 5 is formed from a P-type Si wafer by planar diffusion steps to form first the N-type zones 31, 35, then the P zones 32, 34, thirdly the N+ collector contact and emitter zones 36, 33 and finally the boron diffused P + base contact zone 38 and resistance contact zones 39, 40. On the appropriately apertured oxide layer 37 rhenium, gold or copper, and rhenium layers are successively deposited by evaporation or R.F. sputtering and shaped by photoresist and etching steps, using specified etchants, to provide the contacts and interconnections shown. After deposition of a further oxide layer 43 apertures are etched to expose certain of the interconnections and contacts as at X, where rhenium is then removed and replaced by superposed layers of rhenium and gold which are etched to form a desired interconnection pattern as before. Ohmic contacts with expanded bonding pads can similarly be provided on passivated planar transistors in a common slice from which single devices can be divided. In this case platinum may first be deposited on the contact areas and heated to form platinum silicide prior to deposition of rhenium and gold layers. Contact resistance is lowest when the contact areas are heavily P or N doped (>10 21 atoms/c.c.) or precoated with aluminium.

Pressure dependence of the thermal contact resistance for rough surfaces

Abstract: The contact resistance is expressed analytically as a function of load for elastic and elastoplastic contacts by taking the rough surface as consisting of spherical projections with a normal distribution.

A review of conducting polymers in electrical contact applications

Abstract: A review of recent developments in fretting studies in electrical contacts is presented, focusing on developments in conducting polymer surfaces. Fretting is known to be a major cause of contact deterioration and failure; commonly exhibited as the contact resistance increases from a few milliohms, in the case of a new metallic contacts, to in excess of several ohms for exposed contacts. Two technologies are discussed; firstly extrinsically conducting polymer (ECP), where highly conductive interconnects are formed using metallized particles embedded within a high temperature polymer compound, and secondly; intrinsically conducting polymers (ICPs) are discussed. These latter surfaces are new developments which are beginning to show potential for the application discussed. This paper presents the work on the ICPs using poly(3,4- ethylenedioxythiophene)/poly(4-styrenesulfonate) (PEDOT /PSS) and its blends from secondary doping of dimethylformamide (DMF) PEDOT/PSS. Two different processing techniques namely drop coating and spin coating have been employed to develop test samples and their functionality were assessed by two independent studies of temperature and fretting motion. The review leads to a number of recommendations for further studies into the application of conducting polymers for contacts with micro-movement.

Application of Static Metallic Adhesion Data to Friction

Abstract: The significance of metallic adhesion phenomena are reviewed relative to the sliding friction behavior of metals and alloys. A model is presented for the analysis of sliding friction based upon contact resistance measurements and experimental data presented for the materials combinations ultra-pure iron vs ultra-pure iron, iron 65-ppm carbon vs iron 65-ppm carbon, and 440 C stainless steel vs 440 C stainless steel. It is shown that the behavior observed for these materials combinations under conditions of sliding friction can be predicted from normal force adhesion experiments using a four wire contact resistance bridge circuit. The effects of environment as well as compressive load, sliding frequency, time, and specimen geometry are discussed. It is further shown that significant data are generated by the adhesion technique for the definition of the mechanical properties of the true load bearing area.

Friction and contact resistance for gallium- lubricated low-speed copper sliprings in vacuum

Abstract: Friction and contact resistance for gallium lubricated low speed copper sliprings in vacuum

Materials for light-duty electrical contacts

Abstract: Established materials for light-duty electrical-contact applications are based on the platinum-group metals and gold; silver, copper, tungsten, and their alloys are employed for heavy-duty contacts. The main features of the operation of heavy-duty contacts are arcing and welding, which become important when the power being switched exceeds ∼ 100 W or the current ∼ 1.0 A. In the light-duty field, erosion transfer, mechanical wear, and contact resistance are the phenomena of contact operation that have to be considered. With light-duty contacts, surfaces must be free from tarnish films to ensure low contact resistance: hence the use of the platinum metals and gold. Silver can be used only in restricted light-duty applications where the electrical and mechanical conditions permit rupture of sulphide films.

Current Crowding Effects at Aluminun-Silicon Contacts

Abstract: The magnitude of current crowding and its effects on failure mechanisms at aluminum-silicon contacts have been studied by using an enlarged contact. Current was found to decrease exponentially with distance from the leading edge of the contact. Joule heating in the contact when stressed at high currents caused diffusion of silicon into the aluminum metallization. Accelerated testing at low currents to minimize this effect resulted in diffusion barrier type failures.

Ohmic contacts for gallium arsenide

Abstract: Improved contact resistance to a gallium arsenide body is obtained by alloying the contact metal into the GaAs body in an arsenic vapor atmosphere.

Friction and contact resistance for low speed gallium lubricated sliding electrical contacts of beryllium in vacuum.

Abstract: Reducing friction and contact resistance of sliding electrical contacts of beryllium by gallium lubrication in vacuum

Contact resistance methods of hot machining

Abstract: Electrical contact resistance methods of workpiece heating for hot machining are described. The relative merits of three different techniques, namely cutting tool electrode, bar electrode and roller electrode are discussed. Increases in tool life when hot machining using electrical contact heating are reported and the possible industrial applications discussed.

The effect on thermal contact resistance of the time of application of the load

Abstract: Problems of the effect of the time at which the load is applied on thermal contact resistance are considered. A relationship permitting a determination of the thermal contact resistance as a function of the time of load application is presented.