Compliance Voltage
The compliance voltage is automatic, and is used to limit the power
dissipated in the sample under test. For currents under 1mA the voltage
applied is the maximum 40mV. For currents of 1mA and above the voltage
applied to the source is limited to an absolute maximum of 25V. Above
10mA the voltage is limited so as no more than 0.5W could possibly be
dissipated in the sample, so at 50mA the compliance voltage is limited to
10V, and at 99.999mA it is limited to 5V. Extra caution is required on the
use of currents over 10mA to avoid damaging the samples.
Useful Equations
Sheet resistance = 4.5324 × V/I (units ohms/square)
Bulk Resistivity for a wafer = sheet resistance × wafer thickness in cm (units
ohm.cm)
Bulk Resistivity = 2 ×
π × s × V/I where s is the probe spacing in cm (units
ohm.cm
Siemens are the SI unit of electric conductance and represent the reciprocal
of electrical resistance.
Correction Factors
Probing close to the edge of a sample or on unusual / intermediate shapes
and sizes of sample can mean that correction factors are required.
A broad range of correction factors have been determined by Haldor Topsoe.
At
http://www.jandel.co.uk/topsoe.html you can find all of the pages from
the 1966 (revised 1968) Haldor Topsoe book, "Geometric Factors in Four
Point Resistivity Measurement", with each page available as an individual
PDF file.
Software
The next section of the manual deals with the use of the software supplied
with the RM3000.
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