Four Point Sheet Resistivity Techniques

Abstract

A technique of averaging two resistivity measurements, each made using a different pair of current probes of a square array on an infinite sheet, has been developed. It is shown in theory and practice that when one probe is common to each of the two measurements, an average eliminates all first order errors due to misalignment of the array. An electronic averaging circuit which provides a continuous single meter measurement of sheet resistivity is presented. Data taken with 1.27 mm infinite sheet probe assembly are shown to have a repeatability of ±0.33% (3σ) on a 145 Ω per square sample. This particular system has a useful range of 0.1 to 10 000 Ω per square. The circuity developed for the infinite sheet method is also shown to be applicable to the bounded sheet method (Van der Pauw technique). A novel infinite sheet probe assembly design is illustrated.