The homebuilt sheet resistance measurement station consists of an in-line four point probe that is connected to a current source and a Keithley voltmeter.
A. Turn on power to the voltmeter and current source.
B. Set the voltmeter to the 200 mV scale.
C. Make sure the current source is set to 628 mA.
D. At these settings the measured voltage is equal to the sheet resistance in ohm-square.
E. There are two knobs on the current source, 'Voltage Compliance' and 'Output Selector'.
Never touch the former and make sure the Output Selector is in Standby mode.
F. Place the standard sample (a piece of TCO-coated glass) under the 4 point probe.
G. When the sample is not in contact you should see the voltage jumping around. Put the
four-point probe in contact with the TCO - the voltmeter should read essentially zero.
H. While maintaining contact switch the Output Selector to either + or -. The absolute
value of the voltage is the sheet resistance which should be ~ 12.5 ohm-square for the
TCO. Switching from +/- just changes the direction of the current flow so the induced
voltage changes polarity, however the absolute values should be similar.
I. Remove the TCO sample and repeat the above steps with your sample.
J. Turn off both the current source and voltmeter when finished.
K. Report any deviations or anomolous behavior to your instructor.