Four-wire Method Research Articles

The Nano Tungsten Thin Film and its Contacting Property with Aluminium Electrodes

In this paper we report nanothickness tungsten (W) thin films with nanoscale thickness prepared by DC magnetron sputtering. Three kinds of samples were realized using micromachining technology, including two-wire and four-wire terminal configurations and only Al electrodes. Using four-wire terminal method, we studied on the electrical property of W film and the contacting resistance between W film and Al electrode. The results show that our as-deposited W film is β-W crystal structure and exhibits good resistive property. Al formed a good ohmic contact with W films. Both the resistivity of W film and the contacting resistance declined nearly linearly with the thickness increasing.

Characterization of micro-contact resistance between a gold nanocrystalline line and a tungsten electrode probe in interconnect fatigue testing.

An electromechanically-coupled micro-contact resistance measurement system is built to mimic the contact process during fatigue testing of nanoscale-thickness interconnects using multiple probe methods. The design combines an optical microscope, high-resolution electronic balance, and micromanipulator-controlled electric probe, and is coupled with electrical measurements to investigate microscale contact physics. Experimental measurements are performed to characterize the contact resistance response of the gold nanocrystalline pad of a 35-nm-thick interconnect under mechanical force applied by a tungsten electrode probe. Location of a stable region for the contact resistance and the critical contact force provides better understanding of micro-contact behavior relative to the effects of the contact force and the nature of the contact surface. Increasing contact temperature leads to reduced contact resistance, softens the pad material, and modifies the contact surface. The stability of both contact resistance and interconnect resistance is studied under increasing contact force. Major fluctuations emerge when the contact force is less than the critical contact force, which shows that temporal contact resistance will affect interconnect resistance measurement accuracy, even when using the four-wire method. This performance is demonstrated experimentally by heating the Au line locally with a laser beam. Finally, the contact resistances are calculated using the LET (Li-Etsion-Talke) model together with combined Holm and Sharvin theory under various contact forces. Good agreement between the results is obtained. This research provides a way to measure change in interconnect line resistance directly under a stable contact resistance regime with a two-wire method that will greatly reduce the experimental costs.

Simultaneous fabrication of a through‐glass interconnect via and a bump using dry film resist and submicron gold particles

A process for the simultaneous fabrication of through-glass interconnect vias (TGVs) and gold (Au) bumps using dry film resist and submicron Au particles is proposed. A Ti/Pt/Au layer was sputtered on the top and bottom surfaces of glass vias to improve the adhesion between the glass substrate and submicron Au particles. The submicron Au particles filled the resist holes and glass vias fabricated by photolithography and by the two-electrode method, respectively, and were then sintered. The height and diameter of the fabricated Au bumps were about 20–25 and 200 µm, respectively. The Ti/Pt/Au layer on the surface of the glass substrate was removed by Ar ion milling to isolate each bump electrically. The resistance of a single Au bump and TGV was evaluated using the four-wire ohm method to be about 0.05 Ω. Furthermore, Au bump bonding was demonstrated. Fractured Au bumps and TGVs were observed by scanning electron microscopy after the bonded sample was peeled. It is expected that this fabrication process using a dry film resist and submicron Au particles will be useful in simple packaging processes to form glass interposer substrates or glass integrated circuit chips.

Correlation Between Lateral Photovoltaic Effect and Conductivity in p-type Silicon Substrates

Department of Chemistry, Myongji University, Yongin 449-728, KoreaReceived March 11, 2013, Accepted March 26, 2013The lateral photovoltaic effect (LPE) can be observed in semiconductors by irradiating a light spot positionbetween electrodes on sample’s surface. Because lateral photovoltaic voltage (LPV) is sensitively changed bylight spot position, a LPE device has been tried as a position-sensitive detector. This study discusses thecorrelation between LPV and conductivity in p-type silicon and nano-structured Au deposited p-type silicon(nano-Au silicon), respectively. Conductivity measurement of the sample was carried out using the four-wiremethod to eliminate contact resistance, and conductivity dependence on LPV was simultaneously measured bychanging the light irradiation position. The result showed a strong correlation between conductivity and LPVin the p-type silicon sample. The correlation coefficient was 0.87. The correlation coefficient between LPV andconductivity for the nano-Au silicon sample was 0.41.Key Words : Lateral photovoltaic effect (LPE), Lateral photovoltaic voltage (LPV), Conductivity, Correlationcoefficient, Four-wire method IntroductionThe lateral photovoltaic effect (LPE) has been popularlyused in semiconductor systems

Effect of Sr and Ca dopants on oxidation and electrical properties of lanthanum chromite-coated AISI 430 stainless steel for solid oxide fuel cell interconnect application

Abstract Lanthanum chromite coating occupies a noticeable position as a ceramic coating on metallic interconnects in solid oxide fuel cells because of its excellent electrical conductivity, high oxidation resistance and desirable chemical stability in both oxidizing and reducing atmospheres. In the present work, a sol–gel process based on the dip-coating technique was used to prepare dense and uniform coatings on metallic alloy for interconnect application (AISI 430 type). The effect of strontium and calcium doping into lanthanum chromite structure on electrical conductivity and oxidation behavior of the coated sample has been investigated. The oxidation behavior was evaluated by cyclic oxidation test at 800 °C in lab air. In addition, the area specific resistance (ASR) of the coated and uncoated samples after long-term oxidation was measured through a two-point, four-wire probe method. It was found that, for the coated sample, when compared to the bare metallic one, the addition of Ca into lanthanum chromite coating drastically lowered the oxidation rate and electrical resistance by approximately 2 and 6 times, respectively.

Test Rig for High-Temperature Thermopower and Electrical Conductivity Measurements

A high-temperature test rig to simultaneously measure electrical conductivity and thermopower is described. The apparatus allows to perform measurements in a controlled atmosphere or vacuum to protect oxygen-sensitive materials. A spring-loaded mounting placed in the cold zone reduces the thermal contact resistance between the sample and two metallic blocks (the hot side and the heat sink) even at high temperatures. The hot-side metal block is periodically heated to obtain the thermopower from the slope of ΔV versus ΔT. Conductivity is measured before each thermopower measurement by a linear four-wire method. The automatic data acquisition and analysis are controlled by a LabView-based interface. Two interchangeable setups are possible. The first one uses silver blocks and K-type thermocouples and is suitable for temperatures from 300 K to about 1000 K. The second one uses W blocks and S-type thermocouples to allow higher-temperature measurements since all the hot-zone parts are made of Al2O3, Pt or W. The device was tested using PdAg alloy and Ni rods and, for the low-temperature range, the NIST standard reference material 3451 (bismuth telluride), strictly confirming the reference data.

Touch Screen Technology and its Driver Design in uCLinux

Touch screen input system about hardware connection and driver design in uCLinux were presented in this work. With the respect of hardware, it introduced working mechanism of four-wire resistive touch screen and method of calculating coordinate. Then it presented the hardware connection of touch screen input system including touch screen, touch screen control chip and Microcontroller Unit. With respect of software, it analyzed the characteristic of driver design in uCLinux. Then it divided touch screen working process into six states which were ‘start’, ‘idle’, ‘wait’, ‘read’, ‘error’, ‘end’ and defined the state transition. On this basis, Touch screen driver design was introduced, which mainly included initialization function, clean function, device-opening function, device-releasing function, coordinates-reading function and parameters-setting function. It also gave the arithmetic converting touch screen coordinate to application coordinate.

A Device for Measuring High-TC Superconductor Transition Temperature with Electric Transport and AC Susceptibility Methods Based on Small Cryocooler Cooling

A device for measuring high-TC superconducting transition temperature in a small cryocooler is described which allows a samples temperature to fall steadily from room temperature to 45K. This cryocooler not only meets the high-TC superconductors measurement requirements, but also yields accurate measurement results under ambient conditions. In this device, two measurement methods for measuring high-TC superconducting transition temperature are applied: the electric transport and the AC susceptibility. The former adopts a four-wire method to eliminate the contact resistance between the leads and the sample. During the measurement process the current reversal method for datum processing is applied to eliminate the thermoelectric voltages; this ensures the repeatability error less than 0.4K in the measurement of the superconducting transition temperature. The AC susceptibility method adopts a lock-in amplifier to provide an AC voltage signal for the primary coil, and then lock-in amplifier is used to measure the electrical signals of the secondary coil according to the AC magnetic susceptibility values. The advantage of this device is that by merely changing the position of the sample in the vacuum chamber, the R-T curve and the χ-T curve of a superconducting sample in the same temperature range can be automatically recorded, which provides reliable data for high-TC superconductor transition curve measurement.

Effect of Contact Pressure on the Resistance Contact Value and Temperature Changes in Copper Busbar Connection

This paper discussed the influence of tightness or contacts pressure on copper busbar joints to determine changes in the value of the initial contact resistance and the maximum temperature at the joint due to high current load. The test sample was copper busbar 3 x 30 mm with configuration of bolted overlapping joint. Increasing contact pressure at the joint was measured to find out its effect on the value of contact resistance. The applied pressure was 6 to 36 MPa. Procedure of contact resistance measurement refer to the ASTM B539 standard using four-wire method. The sample subsequently loaded with the current of 350 A for 60 minutes and the maximum temperature at the joint was measured. The result showed that increasing contact pressure at the busbar joint will reduce the contact resistance and maximum temperature. The increase of contact pressure from 6 to 30 MPa causes decreasing contact resistance from 16 μΩ to 11 μΩ. Further increasing of contact pressure more than 30 MPa did not affect the contact resistance significantly. The lowest temperatur of busbar joint of 54°C was reached at a contact pressure of 36 Mpa.

Four-Wire Resistance Measurements of a Bismuth Nanowire Encased in a Quartz Template Utilizing Focused Ion Beam Processing

Four-wire resistance measurements were performed using a bismuth nanowire, 750 nm in diameter, 1.96 mm in length, and encapsulated in a quartz template. One side of the quartz template was polished to allow focused ion beam (FIB) processing, and metal film layers were deposited on the polished side to form electrodes. Nanofabrication was employed to remove a selected portion of the quartz, and FIB processing was used to expose the surface of the bismuth nanowire. A local area of the bismuth wire was successfully exposed, and a carbon electrode was deposited on the bismuth wire in situ by a chemical reaction between the ion beam and phenanthrene gas. Additional carbon deposition on the initial carbon electrode was used to connect to a metal film on the quartz template. In total, four nanofabrications were performed on the bismuth wire to create the desired electrical contacts. The resistivity of the nanowire was measured by a four-wire method to be 1.29 μΩ m at 300 K, corresponding to that of bulk bismuth. The temperature dependence of the resistivity was also measured, and was qualitatively and quantitatively in good agreement with previous calculated and experimental results using other bismuth nanowires. The present results demonstrate the successful development of a technique to fabricate an electrode on a local area of a nanowire using FIB processing to form suitable electrical contacts.

Biological healing mechanism of magnetic porous Ca3 (PO4) 2: an experimental study

Objective To study the causes and theoretical basis for good bone healing ability of magnetic Porous Ca3 (PO4) 2 ( MPTCP). Methods Seven MPTCP specimens with size of 2 cm × 1 cm × 0.5 cm were placed in the material physical system for detecting 42 times and the mean detection value was used to measure the MPTCP curve. The attachment 16451B of impedance spectrometer HP RLC was employed to measure dielectric spectroscopy and dielectric spectroscopy of MPTCP. Four-wire method was used to measure the impedance of MPTCP. Results The magnetic intensity changed rapidly when magnetic field was in a range of-10,000-10,000 Oe. The peak of dielectric spectroscopy and impedance of magnetic bioceramics was in the range of 103-104 Hz. When the external electromagnetic wave of frequency was ≤ 1 000 Hz, electrical impedance of MPTCP was large;while when the electromagnetic wave frequency was≥1 000 Hz, the impedance was relatively small and stable. Conclusion The environmental magnetic fields may change the magnetic and electric behavior of MPTCP and promote the biological healing, which may be the cause for the good bone healing ability of MPTCP. Key words: Fracture healing; Ceramics

Physical properties of monolithic U8 wt.%–Mo

As a possible high density fuel for research reactors, monolithic U8 wt.%–Mo (“U8Mo”) was examined with regard to its structural, thermal and electric properties. X-ray diffraction by the Bragg-Brentano method was used to reveal the tetragonal lattice structure of rolled U8Mo. The specific heat capacity of cast U8Mo was determined by differential scanning calorimetry, its thermal diffusivity was measured by the laser flash method and its mass density by Archimedes’ principle. From these results, the thermal conductivity of U8Mo in the temperature range from 40 °C to 250 °C was calculated; in the measured temperature range, it is in good accordance with literature data for UMo with 8 and 9 wt.% Mo, is higher than for 10 wt.% Mo and lower than for 5 wt.% Mo. The electric conductivity of rolled and cast U8Mo was measured by a four-wire method and the electron based part of the thermal conductivity calculated by the Wiedemann-Frantz law. Rolled and cast U8Mo was irradiated at about 150 °C with 80 MeV 127I ions to receive the same iodine ion density in the damage peak region as the fission product density in the fuel of a typical high flux reactor after the targeted nuclear burn-up. XRD analysis of irradiated U8Mo showed a change of the lattice parameters as well as the creation of UO 2 in the superficial sample regions; however, a phase change by irradiation was not observed. The determination of the electron based part of the thermal conductivity of the irradiated samples failed due to high measurement errors which are caused by the low thickness of the damage region in the ion irradiated samples.

Characteristic of (La 0.8Sr 0.2) 0.98MnO 3 coating on Crofer22APU used as metallic interconnects for solid oxide fuel cell

This study reports the high temperature oxidation kinetics, area specific resistance (ASR), and interfacial microstructure of metallic interconnects coated by (La 0.8Sr 0.2) 0.98MnO 3 (LSM) in air atmosphere at 800 °C. An efficient LSM conductive layer was fabricated on metallic interconnects for solid oxide fuel cells (SOFCs) by using a wet spray coating method. The optimum conditions for slurries used in the wet spray coating were determined by the measurement of slurry viscosity and coated surface morphology. The surface roughnesses of the substrates were increased through sandblast treatment. The adhesive strength of the interface between the coated layer and the metal substrate increased with increased surface roughness of the metallic interconnects. The electrical conductivities of the coated substrates were measured by using a DC two-point and four-wire method under air atmosphere at 800 °C. Of note, the Crofer22APU treated at 1100 °C in N 2 with 10 vol.% H 2 showed long-term stability and a lower ASR value than other samples(heat-treated at 800 °C and 900 °C). After an 8000-h oxidation experiment the coated Crofer22APU substrate, the ASR showed a low value of 23 mΩ cm 2. The thickness of the coated conductive oxide layer was about 10–20 μm. These results show that a coated oxide layer prevents the formation and the growth of scale (Cr 2O 3 and (Mn, Cr, Fe) 3O 4 layer) and enhances the long-term stability and electrical performance of metallic interconnects for SOFCs.

Electric-pulse-induced resistance switching in [formula omitted] ceramics

Nonlinear and hysteretic current–voltage characteristics and electric-pulse-induced resistance (EPIR) switching effects were found in Nd 0.7Sr 0.3MnO 3 ceramics. For samples measured using the two-wire method, a polarity-dependent, stable and reproducible EPIR effect occurs in the whole temperature range measured. The high and low resistive metastates vary with temperature and seemingly can be destroyed by temperatures larger than 400 K. However, for the same sample measured using the four-wire method, no EPIR effect is observed. The result indicates that the EPIR effect is intensively correlated with the interface between the Ag-electrodes and the bulk of the Nd 0.7Sr 0.3MnO 3 polycrystal.

Measuring stress next to Au ball bond during high temperature aging

A real-time signal of the stress caused by a ball bond is recorded during long-term high temperature storage (HTS) without destroying the ball bond, using a piezoresistive integrated CMOS microsensor located next to the Al bond pad (test pad) on a test chip. The sensor is sensitive to in-plane shear stress changes Δ τ xy that arise due to tensile or compressive stress at the test pad. While performing HTS at 200 °C during 400 h, significantly different stress signals are observed with a ball bond (test structure) compared to those observed without a ball bond (reference structure). Simultaneous to Δ τ xy the contact resistance of the bond was directly measured with a four-wire method in which two connection paths lead to the test pad and a second wire bond is made on top of the test ball bond. The contact resistance values measured at room temperature (25 °C) before and after HTS are 2.1 mΩ and 6.1 mΩ, respectively. Effects influencing the stress signal during HTS include volume changes by the growth of intermetallics. The stress increase initially observed during HTS shows bond shrinking corresponding to growth of Au-rich phases which was previously reported to result in volume shrinkage. A subsequent phase of signal drop is observed starting after 200 h, indicating the presence of a different mechanism partly reducing the stress built up previously, and attributed to lateral growth of Al-rich intermetallics, partially consuming the pad Al outside the bond region, and resulting in volume expansion. Finite element models are developed to support the interpretation of the stress signal features. One of the models simulates the shrinking of Au–Al material due to phase transformation. When calibrated to experimental data, the peak underpad Tresca stress level generated during such contraction is 53 MPa, located 2.4 μm inside of the 55 μm diameter bond zone.

Effect of Mechanical Loading on Electrical Conductivity in Human Intervertebral Disk

The intervertebral disk (IVD), characterized as a charged, hydrated soft tissue, is the largest avascular structure in the body. Mechanical loading to the disk results in electromechanical transduction phenomenon as well as altered transport properties. Electrical conductivity is a material property of tissue depending on ion concentrations and diffusivities, which are in turn functions of tissue composition and structure. The aim of this study was to investigate the effect of mechanical loading on electrical behavior in human IVD tissues. We hypothesized that electrical conductivity in human IVD is strain-dependent, due to change in tissue composition caused by compression, and inhomogeneous, due to tissue structure and composition. We also hypothesized that conductivity in human annulus fibrosus (AF) is anisotropic, due to the layered structure of the tissue. Three lumbar IVDs were harvested from three human spines. From each disk, four AF specimens were prepared in each of the three principal directions (axial, circumferential, and radial), and four axial nucleus pulposus (NP) specimens were prepared. Conductivity was determined using a four-wire sense-current method and a custom-designed apparatus by measuring the resistance across the sample. Resistance measurements were taken at three levels of compression (0%, 10%, and 20%). Scanning electron microscopy (SEM) images of the human AF tissue were obtained in order to correlate tissue structure with conductivity results. Increasing compressive strain significantly decreased conductivity for all groups (p<0.05, analysis of variance (ANOVA)). Additionally, specimen orientation significantly affected electrical conductivity in the AF tissue, with conductivity in the radial direction being significantly lower than that in the axial or circumferential directions at all levels of compressive strain (p<0.05, ANOVA). Finally, conductivity in the NP tissue was significantly higher than that in the AF tissue (p<0.05, ANOVA). SEM images of the AF tissues showed evidence of microtubes orientated in the axial and circumferential directions, but not in the radial direction. This may suggest a relationship between tissue morphology and the anisotropic behavior of conductivity in the AF. The results of this investigation demonstrate that electrical conductivity in human IVD is strain-dependent and inhomogeneous, and that conductivity in the human AF tissue is anisotropic (i.e., direction-dependent). This anisotropic behavior is correlated with tissue structure shown in SEM images. This study provides important information regarding the effects of mechanical loading on solute transport and electrical behavior in IVD tissues.

Preparation and electrical properties of the novel mixed ionic-electronic conductors Sm0.9Ca0.1Al1-xMnxO3

The novel mixed ionic-electronic conductors Sm0.9Ca0.1Al1-xMnxO3 （SCAM, x= 0.1—0.5） were prepared by the organic gel method combined with solid state sintering technology. The thermal decomposition and phase inversion process of the gel precursors, crystal strucutres and phase stability of the sinters were studied by using thermogravimetric and differential thermal analysis （TG-DTA） and X-ray diffraction. The electrical conductivities of sintered ceramics in both air and 5%H2/Ar were measured by the direct current four-wire method. The experimental results show that the well-crystallized nanopowders with tetragonal perovskite structure can be obtained after calcining the gel precursors at 900℃ for 5h, the phase stability of SCAM ceramics decreases with increasing Mn content under reduction atmosphere. The electrical conductivity of SCAM ceramics is dominated by p-type electronic conduction and increases with Mn content and temperature. The mechanism of electronic transport is the hopping of p-type small polaron. With increasing calcination temperature and prolonging holding time, both the electrical conductivity and relative density of SCAM9155 become large initially and then decrease. The SCAM9155 sample sintered at 1600℃ for 10h has the highest relative density of 98.2% and electrical conductivity reaching 7.30S/cm in air and 1.91S/cm in 5%H2/Ar at 850℃. The apparent activation energies for SCAM9155 in air and in 5%H2/Ar were calculated to be 0.273 and 0.371eV, respectively. The Ca- and Mn-substituted SmAlO3 with relatively high conductivity may be used as a potential anode material for solid oxide full cells （SOFCs）.

Sol-Gel Insulation Coatings on ${\rm Monel/Fe/MgB}_{2}$ Wires for Coil Development

In this study, preparation, structure, morphology and thermal properties of ceramic insulation coating on Monel/Fe/MgB2 wires, which were fabricated by Hyper Tech Research Inc., using Continuous Tube Forming and Filling (CTFF) process were studied for coil development. Ceramic insulation coatings were prepared by reel-to-reel sol-gel method using solutions of Y and Zr based organometallic compounds. The coating thickness was controlled by number of coating, withdrawal speed and solution chemistry. 29 meter of Monel/Fe/MgB2 wire was insulated by Y2O3-ZrO2 using sol-gel method. Monel/Fe/MgB2 coil was layer wounded and impregnated with stycast. Sister samples of coil were tested between 4.2 K and 30 K with a Variable Temperature Insert (VTI) in a 20 T superconducting magnet using the analog DC pulse four-wire method with 1 (muV/cm) criterion. The sample had a Jc of 0.16 times 105 (A/cm2) at 4 T at 21 K. The surface morphologies and microstructure of sister samples of coil were characterized by ESEM, EDS, DTA, TGA and XRD. Resistance was measured by using HP 4339A High Resistance Meter.

Field dependence of the critical current density ofMgB2/Cu wire for coil development

The critical current density (Jc) of monofilament Cu/MgB2 wire was measured between 4.2 and 30 K with a variable temperature insert (VTI)in a 20 T superconducting magnet using the DC pulse four-wire method with a1 µV cm−1 criterion. The criticalcurrent density, Jc, wasmeasured to be 0.83 × 104 A cm−2 at 3 Tat 21 K and 0.66 × 104 A cm−2 at 8 T at4.2 K for the MgB2 sample,which was annealed at 700 °C for 30 min with 5.8 °C min−1 heating rate under 4% H2–Ar gas flow. Scanning electron microscopy (SEM), electron dispersive spectroscopy (EDS)and x-ray diffraction (XRD) analysis were used to characterize the microstructure of thesamples.

The van der Pauw stress sensor

Piezoresistive sensors fabricated on (100) and (111) silicon surfaces are capable of measuring from four to all six components of the stress state at a point on the surface of an integrated circuit die. Such resistor-based sensors have been successfully designed and fabricated on these wafer planes and have been used successfully for measurement of die stresses in electronic packages by many research teams. In this paper, classical van der Pauw (VDP) structures, traditionally used for sheet resistance measurement, are shown to provide more than three times the sensitivity of standard resistor sensors. A single four-terminal VDP device replaces two resistor rosette elements and inherently utilizes the high-accuracy four-wire resistance measurement method. Theoretical expressions are developed for the change in resistance of the VDP device as a function of the individual stress components resolved in wafer coordinate systems on both the (100) and (111) silicon surfaces, and it is predicted theoretically that VDP devices will exhibit more than three times higher sensitivity to stress than standard resistor sensors. Design, fabrication, and experimental characterization of VDP and resistor test structures are presented for both silicon surfaces, and numerical simulation is used to help resolve discrepancies between theory and experiment. Sources of experimental error are identified, and the 3.16 times sensitivity enhancement of the VDP device is confirmed.