Evolution Of Electrical Resistance Research Articles

Analysis of Electromigration- and Stress-Induced Dynamical Response of Voids Confined in Metallic Thin Films

AbstractA theoretical analysis based on self-consistent dynamical simulations is presented of electromigration- and stress-induced surface morphological response of voids confined in metallic thin films. The analysis predicts the onset of stable time-periodic states for the void surface morphological response, which is associated with current-driven wave propagation on the void surface. This time-periodic response is demonstrated under certain electromigration conditions and detailed response diagrams are presented which map the corresponding parameter space to regions of steady, time-periodic, and unstable surface morphological response. The evolution of the electrical resistance of these thin films also is computed, providing an interpretation for experimentally observed time-periodic response of the electrical resistance of metallic interconnect lines on the basis of current-driven void morphological evolution. In addition, we demonstrate significant effects on the electromigration-induced morphologically stable void migration of mechanical stress application in a metallic thin film. Specifically, we find that under certain electromechanical conditions, elastic stress can cause substantial retardation of void motion, as measured by the constant speed of electromigration-induced translation of morphologically stable voids. More importantly, this effect suggests the possibility for complete inhibition of void motion under stress.

Electrical resistance evolution of Fe thin films during their sulphuration process

An experimental system has been developed to investigate the formation of FeS 2 thin films by sulphuration of Fe films. The change of the film electrical resistance during the whole sulphuration process is measured to investigate the kinetics of the transformation from Fe to FeS 2. Two experimental parameters can be changed in a controlled way: the temperature of the Fe thin film and that of the sulphur source. This allows to accomplish sulphurations at different sulphur pressures with different molecular compositions of the sulphur atmosphere. Preliminary experimental results presented in this paper prove that the experimental system is a powerful tool to investigate the FeS 2 (and other metallic sulphides) formation mechanism.

Consolidación de polvo de hierro mediante sinterización por resistencia eléctrica

A particular kind of hot pressing, in which the powder mass, subjected to pressure, is simultaneously heated by passing through a high-intensity electrical current is described and analysed. Commercial iron powder was used for the experimental work. Special emphasis is given to the densification kinetics. A qualitative microscopic interpretation of densification rate is suggested, based on the hypothesis of partial formation and rapid solidification of liquid phase. This interpretation is supported by the evolution of global porosity and electrical resistance of specimens during the electrical sintering process. The microstructural characteristics of compacts consolidated in the conventional way (cold pressing and furnace sintering) and by electrical resistance sintering are compared.

Interdiffusion in NiFe/Cu/NiFe trilayers: Possible failure mechanism for magnetoelectronic devices

The evolution of electrical resistance, stress, and microstructure during annealing has been studied on 100 nm NiFe(20 wt %)/200 nm Cu/100 nm NiFe trilayers. Irreversible resistance changes and the concentration-depth profiles show that, at and above 200 °C, diffusion of Ni into Cu as well as of Cu into NiFe occurs. The interdiffusion is held for an important failure mechanism of Cu/NiFe-based magnetoelectronic system at elevated temperatures.

An Innovative System for Fretting Wear Testing Under Oscillating Normal Force

Material damage caused by fretting wear is of significant concern in many engineering applications. This paper describes the design and performance of a new machine for the laboratory investigation of fretting wear under oscillating normal force (fretting mode II). The test machine uses an electromagnetic actuator to impose an oscillating normal force between the contacting bodies at a constant force amplitude over a wide range of frequencies. The principle of the actuation mechanism and the fretting wear induced with this particular wear test configuration are outlined in detail. Normal force and electrical contact resistance were measured on-line during fretting mode II wear tests. The performance of the wear test machine is illustrated by data obtained for different materials combinations, namely, hard materials, such as high-speed steel and (Ti,Al)N coatings oscillating against alumina ball counterbodies, and soft materials, such as a tin coating oscillating against the same. In general, wearing of the counterbodies was observed in the slip region. It has been observed that hard coatings and bulk ceramics are prone to fretting fatigue cracking. The evolution of electrical contact resistance in the case of the self-mated soft tin coatings tested under fretting mode II conditions is also reported.

Measuring bubble nucleation temperature on the surface of a rapidly heated thermal ink-jet heater immersed in a pool of water

We describe a method for measuring the average surface temperature of a small square thin metallic film deposited on a silicon substrate and immersed in subcooled water during a voltage pulse of short duration. The thin film studied is a material used in the current generation of commercial ‘desk–jet’printers and comprises a mixture of tantalum and aluminium 65 µm wide and 0.2 µm thick. The experiment uses a bridge circuit with a dynamic amplifier design to measure the evolution of electrical resistance, coupled with a separate calibration of the thin film resistor element with temperature to determine average surface temperature. Voltage pulses of 5 µs typical duration are applied to the thin films. An ‘inflection’ point in the resulting evolution of heater surface temperature identifies bubble nucleation. The calibration of the heater resistance with temperature showed a hysteresis effect that required a burn–in process to stabilize the electrical resistance. With the calibration curve obtained, resistance was converted to temperature and the results analysed. For low power input the average surface temperature exhibited an oscillatory behaviour which indicated a cyclic growth/collapse process often found in nucleate boiling. At higher powers, the oscillatory behaviour disappeared and gave way to an exponential variation of temperature with time similar to a lumped capacitance behaviour of a thermal system. An inflection point in the evolution of surface temperature was found that signified bubble nucleation. The largest heating rate and highest nucleation temperature measured was 0.25 x 109 °C s–1 and 556 K, respectively. This temperature is in good agreement with homogeneous nucleation theory as applied to a surface. The contact angles needed for measured nucleation temperatures to agree with predictions are within the range that is typical for water on metallic surfaces.

Universal mB/T Scaling of the Giant Magnetoresistance in Cu-Co Granular Ribbons Produced by Controlled Melt-Spinning

ABSTRACTStudies of the evolution of electrical resistance in an external applied magnetic field, B, as well as with temperature, T, on Cu86Co14 and Cu92Co8 as quenched and annealed melt-spun ribbons, reveal that magnetoresistance, MR, ΔR(B,T)=R(B)-R(0) scales with B/T. Furthermore, it found that annealing up to 600 °C scales the magnetic moment of the Co-rich superparamagnetic nanoparticles such that, the data for the field dependence of the MR obtained at various temperatures collapses onto the same unique and universal curve f(mB/T) with the Langevin variable mB/T governing the overall behaviour.

The formation of intermetallics in Cu/In thin films

The kinetics of the formation of intermetallics in the Cu–In bimetallic thin film couple have been studied from room temperature to 432 K by measuring the evolution of composite and contact electrical resistance with time and temperature. The resistivity measurements have been supplemented by x-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Copper reacts with indium even at room temperature to form CuIn intermetallic and assuming a model of defect assisted diffusion into the grains, the activation energy averaged over five different samples is found to be 0.40 eV. The grain boundary diffusion is found to occur with an average activation energy of 0.55 eV. XRD confirms the growth of CuIn intermetallic and on annealing at higher temperature, for copper-rich films copper further reacts with CuIn to form Cu9In4. Further evidences of solid state reactions and grain boundary diffusion through Cu grain boundaries have been obtained from SEM study. TEM indicates the growth of the grain size on annealing and confirms the presence of the CuIn phase.

A study of intermetallic compound formation in a copper–tin bimetallic couple

The formation of intermetallics in copper–tin bimetallic couples has been studied from room temperature to 183 °C by measuring the evolution of contact resistance and composite electrical resistance with time and temperature in order to assess the kinetic behavior of the system. X-ray diffractogram (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) studies have also been performed on the samples. As regards bulk diffusion, copper diffuses interstitially into tin rapidly at room temperature with the formation of η′-Cu6Sn5 intermetallic compound. Further diffusion through this phase as evaluated by composite electrical resistivity measurements is given by 0.40 eV, assuming a model of defect-assisted diffusion into the grains. The grain-boundary diffusion is found to occur with an activation energy of 0.78 eV as estimated from contact resistivity measurements. SEM confirms the presence of grain-boundary diffusion of tin in copper, whereas XRD and TEM measurements indicate the growth of η′ intermetallics at room temperature which exists up to 90 °C when it transforms to the ε-Cu3Sn phase. The presence of tin whiskers on the tin surface has also been occasionally observed.

Stabilisation électrique de films résistants en zinc pulvérisé

Zinc sputtered thin films show, after aging, an electric resistance of high fidelity versus the variations of electric field and temperature; fractionned sputtering introduces no disturbance in the evolution of electrical resistance. Data are in qualitative agreement with the consequences of Laville Saint Martin's theories.