The Jandel Four-point Probe System with RM3 Test Unit is a combined constant current source and digital voltmeter.
It has been designed for use in making resistivity measurements in combination with four point probe equipment.
The unit supplies a constant current and displays either the measured voltage or the resultant sheet resistance of the sample in ohms/square (Ω/□), depending on which function has been chosen.
Voltage and sheet resistance can be measured on samples ranging from 5mm X 5mm to 6″ diameter wafers.
The four-point sensing technique allows to measure the electric impedance of a sample avoiding the contact resistance, thus improving the accuracy in measuring low resistances.
This is obtained by using two electrodes for carrying a current (force) and connecting the other two to a high-impedance voltmeter (sense), like in figure.
Since the four probes are equally spaced at a fixed distance, the test unit can extract the sheet resistance of the sample via the Van der Pauw method.