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3.4
Resistivity measurements
The Model 7174A 8 × 12 Low Current Matrix Card can be
used in conjunction with a Model 220 Current Source and a
Model 196 DMM to perform resistivity measurements on
semiconductors. Such measurements can yield such impor-
tant information as doping concentration.
3.4.1 Test configuration
Figure 3-8 shows the basic test configuration to make resis-
tivity measurements on van der Pauw samples. The Model
220 sources current through the samples, while the Model
196 measures the voltage developed across the samples. The
matrix card, of course, switches the signal paths as neces-
sary. In order to minimize sample loading, which will reduce
accuracy, the Model 196 DMM should be used only on the
300mV or 3V ranges. Also, this configuration is not recom-
mended for resistance measurements above 1M Ω due to the
accuracy-degrading effects of DMM loading.
1
Sample 1
4
S G S G
S G
A
B
C
D
E
F
G
H
1
2
Figure 3-8
Resistivity test configuration
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1
Sample 2
Sample 3
2
2
4
4
3
3
S G
S G S G
S G S G S G
S G S G S G
3
4
5
6
7
8
9
10
7174A Matrix Card
707A Switching Matrix
3.4.2 Test procedure
In order to make van der Pauw resistivity measurements,
four terminals of a sample of arbitrary shape are measured.
A current (from the Model 220) is applied to two terminals,
while the voltage is measured (by the Model 196) across the
two opposite terminals, as shown in Figure 3-9. A total of
eight such measurements on each sample are required, with
each possible terminal and current convention. The resulting
voltages are designated V1 through V8.
In order to source current into and measure the voltage
across the sample, specific crosspoints must be closed. Table
3-2 summarizes the crosspoints to close for each voltage
measurement on all three samples from the test configuration
shown in Figure 3-8.
1
2
3
S
HI
G
G
S
LO
G
220 Current Source
(Sources Current through Sample)
S
HI
G
S
LO
G
196 DMM
(Measures Voltage Across Sample)
11
12
Applications
3-7
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