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RESISTIVITY MEASUREMENTS

 

1. RESISTIVITY MEASUREMENTS IN MATERIALS SCIENCE  : Materials science resistivity measurements require in situ and online measurements of resistivity of samples mounted on target ladder with 4 wire method. Resistivity may be measured online and in situ. The samples are a wide range of materials from semiconductors, dielectrics, seminsulators to insulators. Several resistivity measurement programs have been developed to accomplish the requirements of materials science resistivity measurements.

2. MEASUREMENT OF RESISTIVITY  : Resistivity data is normally acquired by 2 methods- the two wire method and the four wire method. The four wire method gives us accurate resistance measurements and is suitable especially for low values of resistance. The two wire method is more suitable for measurement of higher resistances and where some error is acceptable.

2.1 RESISTIVITY MEASUREMENT : Resistivity is simplywhere R is the resistance of the sample, A is the cross sectional area and l is the length between electrodes. As A and l are constant for any experiment with fixed contacts and hence resistivity is proportional to the resistance in an experimental setup.

2.2 RESISTIVITY MEASUREMENTS WITH 4 WIRE METHOD

 

n 4 wire resistance measurement, we supply the sample with some known current I from a current source and measure the voltage V generated across the sample with a separate set of wires. Resistance is given by V/I. However this is not the case practically where the sample resistance is often very low and the measured voltage becomes comparable to the induced thermal emfs. A practical low resistance measurement setup shown in figure shows the thermal sources as emf sources in series with the sample.

instead of R=V_R/I and there is an error of Vth/I in the measurement.

 

Tow up to date resistivity meters with measuring cells