Contact four-point probe technique

A theoretical treatment of the four-point probe technique is based on the consideration of the potential around the point contacts and the resulting current paths. For a semiinfinite sample and infinitesimal small point contacts, it can then be shown (Valdes, 1954 Schroeder, 1998) that the resistivity of the material generally results as... 

Surface conductivity of glass or of thin films on glass is often measured in terms of sheet resistance (ohms per square, or Q/D) using a four-point probe technique. Electrically contacting point probes are placed at the four comers of a square on the surface or the fihn. A current I is allowed to pass through two adjacent probes, and the potential difference V developed across the other two probes is measured. Sheet resistance in this arrangement is calculated as... 

Conductivity of (BN) iSO F and comparison with Cg SO F. In our early studies (12), a four-probe technique was employed, in which four platinum wires were used for electrical contact, and the samples were prepared by pressing powdered polycrystalline material into pellets. Because the platinum wires and the pellet surface are not ideally flat, a uniform intimate contact could not be assured between the wires and the pellet. The boundary effects due to the polycrystalline nature of the pellet sample also render such conductivity measurements unreliable. Attempts to use a contactless radio frequency inductive technique described by Zeller et al. (22) failed because this technique is not sensitive to low conductivities. A four-point probe measurement (21) on an intercalated highly oriented boron nitride sample was used in the present set of conductivity measurements. The <7295k 1.5Scm . The specific conductivity increased with decreasing temperature (see Fig. 1), it having nearly twice the room temperature value at 77 K. This indicates metallic behavior. 

Most electrical characterization techniques require physical contacts between the wafer and the measuring instrument. They can be nonpermanent contacts (e.g. four-point probe) or permanent contacts (e.g. evaporated metal). For some applications such permanent contacts are not permissible. They may, for example, create damage or leave residues that are deleterious during subsequent processing. Non-contacting methods allow complete inspection of all wafers because no physical contact is made. 

The electrical conductivity of low-resistance polymers and polymer composites can be determined by two four-electrode techniques the standard method for testing bar-shape specimens of semiconductors and conductors and the four-point probe method developed for nondestructive testing of sheets and thin films. In both methods two external probes (electrodes) are used as the cunent electrodes and the two inner probes are used to measiue the voltage drop. Using four probes eliminates possible erroneous results due to the probe resistance and the contact resistance between the electrode and the tested material. Hiis method also allows the elimination of the influence of the barriers at the electrode/material contact on the temperature dependence of the conductivity. 

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