Construction of a PC-based resistivity measuring instrument using four-point probe

Leo M. Bordey

Date

6-1991

Degree

Bachelor of Science in Applied Physics

College

College of Arts and Sciences (CAS)

Adviser/Committee Chair

Feliciano T. Bantila Jr.

Abstract

A resistivity measuring instrument was constructed using a four-point probe method. The probe was made of 0.375 mm diameter stainless steel needles. Voltage across the inner two probes was measured at room and at increasing temperature. A high input impedance voltmeter circuit was constructed to measure the potential drops. An LM234 current source device was designed to function as temperature sensor which exhibits a linear output of 20 mV/'K. Both analog signals were inputs to an analog-to-digital converter which was configured to have a resolution of 20 mV per binary bit. The instrument was interfaced effectively to a computer which reads the signals sent to it by the analog-to-digital converter via its data bus. The four-point probe measurements did not coincide with expected results due to several factors; of prime significance is the non-ohmic contact between probe needles and semiconductor. Ohmic contact is met when a plot of current thru the probe against the voltage across it yields a constant I-V ratio for negative and positive currents.

Language

English

Location

UPLB Main Library Special Collections Section (USCS)

Call Number

Thesis

Document Type

Thesis

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