Four-point technique

Hao, Q. Kulikov, V. Mirsky, V. M. Investigation of contact and bulk resistance of conducting polymers by simultaneous two- and four-point technique. Sens. Actuators. 2003, B94, 352-357... 

Fig. C.IO. A sheet resistivity and linewidth test structure. The sheet resistance can be measured in the van der Pauw feature, and the resistance of the line can be measured using a two, three, or four point technique. The bar is nominally 10 squares, so the degree of overetch can be quantified.

Specific Electric Conductivity The specific electric conductivities a of LGS, LGN and LGT were measured using a four-point technique at temperatures between 795 and 1000 K on crystal slices cut perpendicular to the Z-axes. The temperature dependence of the conductivities in dielectric materials with a limited defect density are caused by localized electronic states, and thus the data yield a straight line in a plot of In c versus 1/T, the slope of which is a measure of the activation energy AE of the charge carriers in a Mott-type transition model. These activation energies were found to be 1.1 (LGS), 1.0 (LGN) and 0.9 (LGT) eV, respectively. The rather strong increase in electric conductivity (LGS 10 Q cm at 530°C, 5 X lO- Q- cm- at 730 °C LGT lO- fi- cm" at 600 °C, 8 x 10-"Q- cm- at 730 °C) appears to limit the high-temperature applications of these materials. 

Electrical conductivity or resistivity is a key physical property of all materials of interest in the electronics industry. The manner in which a material opposes the flow of electric current can be determined through several measuring methods, such as eddy current testing, the two-point technique, the four-point technique, and the van der Pauw technique (Boudenne et al. 2011). 

Measurement Technique. Rectangular stripes of silver paint are applied to the surface of each sample at regularly spaced intervals to form electrical contacts. Wires are attached to the samples by spring-loaded metal clips placed on the silver-paint electrodes. A comparison of two-point and four-point measurements showed that contact resistance between the sample and the silver-paint electrodes can be significant, especially for composites close to the percolation threshold. All measurements reported here are made with a four-point technique [72] in the linear (ohmic) range of the resistance versus voltage characteristic, and shpw no significant time dependence. 

Diffusivities of various elements ate determined experimentally. Dopant profiles can be determined. The junction depth can be measured by chemically staining an angle-lapped sample with an HE/HNO mixture. The -type region of the junction stains darker than the n-ty e region. The sheet resistivity can also be measured using a four-point probe measurement. These two techniques ate used for process monitoring. 

It is worth briefly pointing out the difference between in-line and online analysis. In-line analysis does not involve removal of the sample from the reaction vessel, for example in determining water or oxygen content. On-line analysis does involve removing a sample, usually as a side stream, which adds to the complexity of the plant since the sample off-take equipment will often need to be built to the same integrity as the plant. There are four common techniques employed ... 

Measurement of electrical sheet resistance (two- or four-point method). The simplest technique for measurement of sheet resistance of polymer samples is... 

To minimize the current flow through the sample, an ac four-point probe technique was used to monitor the conductivity of the sample with a lock-in amplifier (Stanford Research Systems, model SR 830 DSP). The lock-in amplifier enabled us to measure very low voltages without noise problems. 

Conventional two-electrode dc measurements on ceramics only yield conductivities that are averaged over contributions of bulk, grain boundaries and electrodes. Experimental techniques are therefore required to split the total sample resistance Rtot into its individual contributions. Four-point dc measurements using different electrodes for current supply and voltage measurement can, for example, be applied to avoid the influence of electrode resistances. In 1969 Bauerle [197] showed that impedance spectroscopy (i.e. frequency-dependent ac resistance measurements) facilitates a differentiation between bulk, grain boundary and electrode resistances in doped ZrC>2 samples. Since that time, this technique has become common in the field of solid state ionics and today it is probably the most important tool for investigating electrical transport in and electrochemical properties of ionic solids. Impedance spectroscopy is also widely used in liquid electrochemistry and reviews on this technique be found in Refs. [198 201], In this section, just some basic aspects of impedance spectroscopic studies in solid state ionics are discussed. 

Four-point probe measurements are very reliable, but the technique has limitations, because, as more highly resistive materials are examined, the... 

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