Small Resistance Changes Research Articles

Failure criteria of flip chip joints during accelerated testing

The criteria used to determine electrical failure was explored during accelerated testing of underfilled flip chip joints as a function of both different thermal cycling conditions and different sampling methods. The criteria was based on resistance measurements of daisy-chained solder joints monitored in situ and by endpointing. The sensitivity of the resistance criteria was found to depend strongly on test conditions and often could not be categorized into simple pass/fail groupings. Also, extremely small resistance changes were measured for joints with through-cracks generated by fatigue. Experimental error associated with fixing the cycles to failure was minimized by monitoring the absolute changes in resistance as a function of cycling time while simultaneously measuring the temperature dependence of resistance as the joints degrade. Failure times derived from interval part monitoring closely approximated in situ monitoring, but the resistance measurements for mild cycling conditions required a high degree of accuracy. Finally, a tunneling model is proposed to explain the resistance behavior of cracked joints.

Track width definition of giant magnetoresistive sensors by ion irradiation

We describe the concept of using irradiation with light energetic ions in conjunction with a mask to define the edges of giant magnetoresistive sensors without milling. The irradiated material undergoes substantial interfacial mixing, and consequent loss of magnetoresistance (MR), accompanied by small changes in resistivity, and no significant change in magnetic moment. The ion species and energy may be chosen to minimize lateral scattering as they pass through the sensor film. Modeling of a perfect mask edge above a sensor film of thickness /spl sim/240 /spl Aring/ irradiated with a well-collimated ion beam indicates that sensor edge definition of /spl plusmn/20 /spl Aring/ is achievable-a vast improvement over sensor edges generated using ion milling, which may run to hundreds of Angstroms in width. Experimental data from irradiation of typical NiO, IrMn, NiMn and PtMn-based spin valves using 700 keV N/sup +/ ions indicate that doses between 10/sup 15/ and 10/sup 17/ ions/cm/sup 2/ are sufficient to diminish the MR of the films to below 5% of the as-grown value. Changes in MR caused by the irradiation are stable against annealing at temperatures typical for setting these sensors.

Taurine activates GABA A but not GABA B receptors in rat hippocampal CA1 area

We investigated if taurine, an endogenous GABA analog, could mimic both hyperpolarizing and depolarizing GABA A-mediated responses as well as pre- and postsynaptic GABA B-mediated actions in the CA1 region of rat hippocampal slices. Taurine (10 mM) perfusion induced changes in membrane potential and input resistance that are compatible with GABA A receptor activation. Local pressure application of taurine and GABA from a double barrel pipette positioned along the dendritic shaft of pyramidal cells revealed that taurine evoked a very small change of membrane potential and resistance compared with the large changes induced by GABA in these parameters. Moreover, in the presence of GABA A antagonists, local application of GABA on the dendrites evoked a GABA B-mediated hyperpolarization while taurine did not induce any change. Taurine neither mimicked baclofen inhibitory actions on presynaptic release of glutamate and GABA as judging by the lack of taurine effect on paired-pulse facilitation ratio and slow inhibitory postsynaptic potentials, respectively. These results show that taurine mainly activates GABA A receptors located on the cell body, indicating therefore that if taurine has any action on the dendrites it will not be mediated by either GABA A or GABA B receptors activation.

Lanthanum doped SnO 2 and ZnO thin films sensitive to ethanol and humidity

Thin SnO 2 and ZnO films doped with 0–7 at.% La were deposited by spray pyrolysis. The electrical resistance change of films doped with different lanthanum concentrations was investigated in the presence of 1.5 vol% ethanol vapour in the air at temperatures varying between 150 and 400 oC. The ethanol sensitivity of 3% La-doped SnO 2 films was found to be about 30. Zinc oxide films doped with 3% La showed a much higher sensitivity ( S = 350). All the films exhibited very short response and recovery times (less than 60 s.) at 300°C. Increasing of La content in the films up to 7% deteriorate the ethanol sensitivity. The enhancement of ethanol sensitivity for ZnO and SnO 2 films doped with 3 at.% lanthanum can be explained by its double action on the films surface – increasing of surface basicity and decreasing of the size of crystallites. The undoped and doped SnO 2 films show small change in resistance in the range of relative humidities 20–95% RH. The electrical resistance of La doped ZnO films is more strongly influenced by the relative humidity than the resistance of the doped SnO 2 films, but these dependencies are not linear.

Injection and detection of a spin-polarized current in a light-emitting diode

The field of magnetoelectronics has been growing in practical importance in recent years1. For example, devices that harness electronic spin—such as giant-magnetoresistive sensors and magnetoresistive memory cells—are now appearing on the market2. In contrast, magnetoelectronic devices based on spin-polarized transport in semiconductors are at a much earlier stage of development, largely because of the lack of an efficient means of injecting spin-polarized charge. Much work has focused on the use of ferromagnetic metallic contacts3,4, but it has proved exceedingly difficult to demonstrate polarized spin injection. More recently, two groups5,6 have reported successful spin injection from an NiFe contact, but the observed effects of the spin-polarized transport were quite small (resistance changes of less than 1%). Here we describe a different approach, in which the magnetic semiconductor BexMnyZn1-x-ySe is used as a spin aligner. We achieve injection efficiencies of 90% spin-polarized current into a non-magnetic semiconductor device. The device used in this case is a GaAs/AlGaAs light-emitting diode, and spin polarization is confirmed by the circular polarization state of the emitted light.

Anesthetic Management of the Parturient with Protein S Deficiency and Ischemic Heart Disease

Anesthetic Management of the Parturient with Protein S Deficiency and Ischemic Heart Disease

A reliable and environmentally friendly packaging technology-flip-chip joining using anisotropically conductive adhesive

There is an increasing demand to move the radio base station closer to the antenna for future mobile telecommunication systems. This requires a significant reduction in weight and volume and increased environmental compatibility. This work provides an evaluation of environmental impact and reliability when using anisotropically conductive adhesives (ACA) for flip-chip joining in radio base station applications. Conventional FR-4 substrate has been used to assemble a digital ASIC chip using an anisotropically conductive adhesive and flip-chip technology. The chip has a minimum pitch of 128 /spl mu/m with 7.8 mm in chip 8 and has in total 144 bumps with a bump size of 114/spl times/126 /spl mu/m/sup 2/. Bumping was made using electroless nickel/gold technology. Bonding quality has been characterized by optical and scanning electron microscopy and substrate planarity measurement. The main parameters affecting quality are misalignment and softening of the FR-4 substrate during assembly, leading to high joint resistance. Reliability testing was conducted in the form of a temperature cycling test between -40 and /spl plusmn/125/spl deg/C for 1000 cycles, a 125/spl deg/C aging test for 100 h and a 85/85 humidity test for 500 h. The results show that relatively small resistance changes were observed after the reliability test. The environmental impact evaluation was done in the form of a material content declaration and a life cycle assessment (LCA). By using flip-chip ACA joining technology, the content of environmentally risky materials has been reduced more than ten times, and the use of precious metals has been reduced more than 30 times compared to conventional surface mount technology.

Fatigue damage characterization in carbon fibre composite materials using an electrical potential technique

Changes in electrical resistance during static and fatigue loading of unidirectional and cross ply carbon fibre reinforced polymer composites have been studied. The carbon fibres in the study were T300 and the matrix resins were Hexcel 914 and 920. It was found that changes in resistance during static tensile testing were about three per cent of the original resistance of the samples, while fatigue testing caused resistance changes of up to 10% of the original resistance, immediately prior to final failure. The initial linear portion of the resistance increase on static testing was reversible and could be attributed to reversible elastic strains in the fibres; later non-linear changes were a consequence of fibre fracture and were irreversible. Changes in resistance during fatigue also contained both reversible and non-reversible components. It was found that during fatigue testing the initial changes in resistance caused by the first few thousand cycles could be correlated with the eventual life. Samples with large initial resistance change had reduced lives compared with those with small changes in resistance. Fatigue lives of composite laminates may thus be predicted from monitoring of initial resistance changes. Many of the results could be explained via the parallel resistance model of conduction in composite laminates.

Crystal Structure and Magnetic Properties of Fe<sub>2</sub>OBO<sub>3</sub>

Structural (a = 3.1688(1), b = 9.3835(3), c = 9.2503(3) �, ? = 90.220(1)�) and magnetic properties of a new mixed-valent oxoborate Fe2+Fe3+OBO3 were studied from 3-337 K. Low-temp. neutron powder diffraction and high-temp. synchrotron x-ray powder diffraction show a change in the symmetry of the warwickite type structure from monoclinic (P21/c) to orthorhombic (Pnma) at 315 K and demonstrate that the 2 Fe sites are occupied by an exact av. Fe2.5 valence at all temps. Magnetization measurements reveal an ordering transition at Tc = 155 K below which there is a small ferromagnetically ordered component. Neutron diffraction measurements below Tc show an apparent antiferromagnetic ordering but the magnetization measurements suggest that this is an L-type ferrimagnetic behavior. Resistivity measurements show a small change in resistivity at 315 K. [on SciFinder(R)]

Landslide surveys in Tertiary soft rock areas using HEM

This paper describes case histories for landslide surveys in Tertiary soft rock areas in Japan using a Helicopter-borne Electromagnetic (HEM) system operating at five frequencies between 220 Hz and 137,500 Hz.The usual method for conducting landslide surveys consists of airphoto interpretation, field investigation, and test borings. The ground dc resistivity method is seldom used for landslide surveys, because of the intermixture of topographic effects, the lack of uniformity of data and the difficulty of obtaining closely spaced survey lines along the slopes. On the other hand, HEM data are densely sampled, are very uniform over a survey area and are not as likely to suffer from topographic effects since the HEM “footprint” is relatively small compared with terrain changes. These factors make HEM measurements ideal for detecting the small resistivity changes caused by the landslides.HEM results show that the landslide locations coincide well with anomalously low resistivity zones in HEM apparent resistivity profiles and maps. This correlation occurs because the sliding surfaces of Tertiary type landslides are always accompanied by montmorillonite clay, which lowers the resistivity of the rocks. Furthermore, landslide locations very often correspond to an upheaval or raised pattern of low-resistivity zones in imaged AEM-resistivity sections. Shallow low-resistivity zones such as sliding surfaces also lower the apparent resistivity values at lower frequencies.The HEM method is effective in detecting and delineating landslides associated with cohesive soil, collapsed soil, or weathered zones in areas of Tertiary soft rocks.

The modeling of resistance changes in the early phase of electromigration

Sensitive measurements of the evolution of the resistance of aluminum based metallisation stripes that have been electrically stressed with large current densities show a rather unpredictable initial change followed by a more or less linear increase (less than 1%) for a considerable period of time. Ultimately, breakdown will occur preceded by an erratic behavior of the resistance. This paper reviews existing models for these early changes. It reviews the importance of a generation term for vacancies separate from a divergence of flux term in the explanation of small resistance changes in these models and proposes an alternative view that explains the linear behavior of the resistance change and can also incorporate a variety of initial changes depending on initial mechanical stress conditions. In this model it is assumed that electron wind can create vacancies in the grain boundary regions that are further redistributed because of the electrical current. In this creation process less mobile damage is created, that contributes to the scattering of electrons and thus increases the resistance.

Determination of the Effects of Strain on Electrical Resistivity in Patterned Interconnects

AbstractSensitive measurements of electromigration-induced resistance changes in metallization interconnects have been previously interpreted as due to precipitation effects, vacancy concentration changes and local stress changes (due to the piezoresistance effect). The latter have the potential for characterizing the early stages of electromigration-induced diffusive phenomena prior to larger scale effects such as voiding and subsequent localized joule heating which seriously complicate the interpretation of small resistance changes. However the utility of such “early" measurements is also hindered by lack of an accurate knowledge of the stress coefficient of resistivity as a proper characterization of the change in strain state of the Al. We present measurements of the effects of volumetric strain on the resistivity of Al interconnects where the strain is induced by thermal expansion mismatch between the Al and surrounding passivations. The piezoresistance effect is characterized by properly accounting for the degree of interconnect constraint (and volumetric strain) induced by thermal expansion mismatch as a function of temperature for both passivated and unpassivated lines. Sensitive interconnect resistance versus temperature measurements for differently constrained interconnects (with different volumetric strains) thus allows for the measurement of the piezoresistance effect. Other effects such as solute or vacancy concentration changes with temperature are minimized since the measurements are performed by cooling the passivated and unpassivated lines from room temperature to approximately 70K, rather than by significant heating above room temperature. We determine the piezoresistance coefficient, defined as dρ/dɛv, where ρ = resistivity and ɛv = volumetric strain, to be approximately 1.5−5 Ω-cm, in rough agreement with previous work. The interpretation of sensitive resistance measurements as volumetric strains in isolated sections of interconnects undergoing electromigration-induced diffusion processes is described for specialized test structures.

Apparatus for Extensional Viscosity Measurements

Although most analyses in tribology deal with the behavior of fluids in shear, many fluids, such as greases or printing inks, can develop significant forces when subjected to pure extension. These forces can impact performance, especially in the exit region of tribological interfaces. The resistance of a fluid to an imposed shear rate is a measure of the fluid’s shear viscosity (usually just referred to as its viscosity). The resistance of a fluid to an imposed extensional strain rate is a measure of the fluid’s extensional viscosity. In this paper, two techniques for the measurement of extensional forces are discussed. A subsequent companion paper will discuss interpretation of the force data in terms of extensional viscosity. Both techniques described have the advantage of a dimensionally small measurement element. The first technique involves the use of a vapor deposited surface pressure transducer. This transducer is a thin strip of ytterbium. The electrical resistance of ytterbium is pressure sensitive. Small changes in resistance can be related to extensional stress. The extensional viscometer apparatus consists of two counter-rotating cylinders. As the fluid exits the nip between the cylinders, the extensional stress is detected by a transducer attached to one of the cylinders. The second technique discussed herein involves the use of a small-beam transducer in conjunction with the counter-rotating cylinder apparatus. The deflection of the beam due to the fluid’s extensional force is detected and interpreted in terms of extensional stress as a function of strain rate at the exit of the nip. Extensional stresses of several hundred thousand Pa have been measured.

Cell–cell coupling between CO 2-excited neurons in the dorsal medulla oblongata

Anatomically coupled neurons (17 of 137) and non-coupled neurons (120 of 137), in and near the nucleus tractus solitarius and dorsal motor nucleus (i.e. solitary complex), were studied by rapid perforated patch recording in slices (rat, 150–350 μm thick, postnatal day 0–21) before, during and after exposure to hypercapnic acidosis. Anatomical coupling refers to the intercellular transfer of Lucifer Yellow and Biocytin into adjoining neurons, presumably via gap junctions [see Dean et al. (1997) Neuroscience, this volume]. Eighty-six per cent of the anatomically coupled neurons (12 of 14) were depolarized by hypercapnic acidosis, a response referred to as CO 2 excitation or CO 2 chemosensitivity. In all, 28% (12 of 43) of the CO 2-excited neurons were anatomically coupled to at least one other neuron. None (0 of 39) of the CO 2-inhibited neurons were anatomically coupled, and only 4% (two of 46) of the CO 2-insensitive neurons were anatomically coupled. Increasing the fractional concentration of CO 2 from five to 10 and 15% in constant bicarbonate (26 mM) decreased intracellular pH (control 7.3–7.4, 22–25°C) by ∼1.0 and >1.5 pH units, respectively, as measured using the pH-sensitive fluorescent dye, 2′,7′-bis (2-carboxyethyl)-5,6-carboxyfluorescein. Nine of the anatomically coupled neurons (six CO 2-excited, one CO 2-insensitive and two unidentified) exhibited spontaneous electrotonic postsynaptic potential-like activity, suggesting that they were also electrotonically coupled. During hypercapnic acidosis, the amplitudes of electrotonic postsynaptic potentials were unchanged, concomitant with small changes in input resistance. The frequency of electrotonic postsynaptic potentials increased during hypercapnic acidosis in many anatomically coupled neurons (eight of nine), indicating that both neurons of the coupled pair were stimulated. Cell–cell coupling occurred preferentially in and between CO 2-excited neurons of the solitary complex. Further, CO 2-excited neurons were not electrotonically uncoupled during intracellular acidosis, in contrast to the effect that decreased intracellular pH has on many other types of coupled cells. It was not determined whether anatomical coupling was affected by hypercapnic acidosis since dye mixture was always administered under normocapnic conditions. The high correlation between anatomical coupling, electrotonic coupling activity and CO 2-induced depolarization suggests that cell–cell coupling is an important electroanatomical feature in CO 2-excited neurons of the solitary complex. CO 2-excited neurons have been hypothesized to function in central chemoreception for the cardiorespiratory control systems, suggesting that cell–cell coupling may contribute in part to central chemoreception of CO 2 and H +.

Current patterns in magnetically inhomogeneous conductors

We determine the current distributions in conducting strips whose resistivity and Hall angle vary with longitudinal position along the wire. We consider isolated, finite rectangular Hall bars between semi-infinite leads, as well as periodic structures. The approaches used avoid standard approximations such as perfectly-conducting leads, well-separated interfaces, or small resistivity changes. We find that as an isolated Hall bar is shortened, one enters a regime of closed current loops in the classical Hall effect. Related behavior is found for periodic Hall patterns.

A simple digital 3-lead ohmmeter

A circuit technique to measure a small difference between two resistors or small changes in a transducer resistance is designed by employing a dual-slope analogue-to-digital converter with a multiplexed preamplifier. A 3.5-digit, 0.1 degrees C resolution, 3-lead platinum thermometer was built successfully.

An investigation of solder joint fatigue using electrical resistance spectroscopy

Interconnect electrical resistance is examined as a possible bases for a reliability tool. Measurements are reported of the resistance change of lap shear (60% Sn-40% Pb) solder joints as a function of fatigue. The expected dependence of electrical resistance on elastic strain, plastic deformation, and cyclic fatigue is reviewed. An analytical framework is developed to examine the observed electrical resistance change. A technique called resistance spectroscopy was used to measure the small resistance change resulting from the strain and fatigue in the presence of much larger resistance changes resulting from temperature and other fluctuations. The level of the noise in the resistance measuring system used for the lap shear joints was less than one nano-ohm. The lap shear solder joints exhibited a systematic resistance change as the specimens were cycled toward failure. Initially the average resistance increased, followed by a much stronger decrease, and lastly increased markedly as crack propagation began. The decreasing-resistance portion of this signature occurs prior to crack initiation, and can be used to detect incipient solder joint failure more quickly and with greater ease than present techniques.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

1/f noise produced by the random motion of the carriers crossing potential barriers in semiconductors

A new model for 1/f noise is discussed. When carriers in a semiconductor are separated by a potential barrier into two groups, some of the carriers climb over the barrier and move into the other group as a series of random events. If one group is in a trap, the number of the carriers in the trap varies with time. The probability of the occurrence of the first return to the initial state is in inverse proportion to the cube root value of the number of random events. The number of carriers is proportionate to the electric charge. The charge induces change in the resistance in the local area near the trap. The area is so small that the semiconductor shows the small resistance change of a square wave form. The distribution of the random square wave is represented by the Poisson distribution and its autocorrelation function has a Lorentzian spectrum. The characteristic of first return to the initial state shows that the probability of the Lorentzian spectrum is in inverse proportion to the wavelength. A 1/f spectrum is obtained by the superposition of the spectra.

Renovascular resistance in primary hypertension

To gauge the influence of renovascular resistance changes on blood flow velocity pulsatility in kidneys of hypertensive patients by means of the ultrasonic colour and pulsed-wave Doppler method, since we have previously shown in normotensive subjects that the blood flow velocity pulsatility in renal interlobar arteries varies with changes in renovascular resistance. In six male patients with primary hypertension, renal blood flow velocity profiles were investigated by means of duplex ultrasound. Single-kidney renovascular resistance was assessed by measurements of split renal function (gamma-camera renography), renal plasma flow (steady-state para-aminohippurate clearance) and cuff blood pressure. The pulsatility index of the blood flow velocity spectrum in the renal interlobar artery and renovascular resistance were measured either at rest, during infusion of angiotensin II, or after angiotensin converting enzyme inhibition. A significant correlation existed between pulsatility index and renovascular resistance (r = 0.50, P < 0.002), which did not improve after correction for the blood pressure pulsatility. Changes of pulsatility index were more closely related (r = 0.64, P < 0.001) to the corresponding changes in renovascular resistance. With the two-dimensional image-guided colour and pulsed-wave Doppler method it is possible to assess semiquantitatively small intra-individual changes in renovascular resistance in hypertensive patients by means of pulsatility index measurements. Pharmacologically induced alterations in renovascular haemodynamics may therefore be evaluated with this technique.

Single-plane multifrequency electrical impedance instrumentation

When tissue interacts with electromagnetic radiation it exhibits resistivity and permittivity changes, which decrease with frequency. Above 100 kHz it is expected that dielectric changes in tissue (permittivity) will allow one to distinguish damaged and necrotic tissue. Furthermore, tissue impedance at medium frequencies (100 kHz-1 MHz) have not been well characterized. The aim of this work was to design instrumentation for an impedance tomographic spectrometer to cover the minimum band 10 kHz-1 MHz. In order to produce images sensitive to small changes in resistivity, voltage measurement must be accurate to at least 0.1%. Using commercially available operational amplifiers, PSPICE simulations demonstrated 0.1% accuracy up to 800 kHz, falling off to 0.5% at 1 MHz. Implementation achieved a reasonably flat amplitude (+or-0.5 dB) and a phase shift of 50 degrees from 10 kHz to 3 MHz and a receive response of 0.13 dB to 5 MHz and phase shift of -40 degrees at 3 MHz. With channel correction this design will provide useful readings up to 3 MHz.