Resistivity Calculations; Semiconductor Iv Characterization; Test Configuration - Keithley 7174A Instruction Manual

Table 3-2
Crosspoint summary for resistivity measurements
Voltage Sample #1
V A1 B4
1
V A4 B1
2
V A4 B3
3
V A3 B4
4
V A3 B2
5
V A2 B3
6
V A2 B1
7
V A1 B2
8

3.4.3 Resistivity calculations

Once the eight voltage measurements are known, the resis-
tivity can be calculated. Two values of resistivity, ρ
are initially computed as follows:
1.1331 f
A
ρ
= ------------------------------------------------------------------------ -
A
1.1331 f
ρ B
= ------------------------------------------------------------------------ -
B
Where: ρ and ρ are the resistivities in Ω -cm
A B
t is the sample thickness in cm
S
V through V are the voltages measured by the
1 8
Model 196
I is the current through the sample in amperes
f and f are geometrical factors based on sample
A B
symmetry (f =f =1 for perfect symmetry).
A B
Once ρ and ρ are known, the average resistivity, ρ
A B
can be determined as follows:
ρ
=
AVG
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Crosspoint closed
Sample #2
E3 F2 A5 B9
E3 F2 A8 B5
E2 F1 A8 B7
E2 F1 A7 B8
E1 F4 A7 B6
E1 F4 A6 B7
E4 F3 A6 B5
E4 F3 A5 B6
and ρ
A
( )
t V +V –V –V
S 2 4 1 3
I
( )
t V +V –V –V
S 6 8 5 7
I
AVG
ρ ρ
+
A B
------------------ -
2
Sample #2
E7 F6 A9 B12 E11
E7 F6 A12 B9 E11
E6 F5 A12 B11 E10
E6 F5 A11 B12 E10
E5 F8 A11 B10 E9
E5 F8 A10 B11 E9
E8 F7 A10 B9 E12
E8 F7 A9 B10 E12
3.5

Semiconductor IV characterization

A source measure unit such as the Model 236, 237, or 238 is
used to test and characterize many types of devices. One of
B
these is semiconductor devices. The following paragraphs
explain the basic scheme and connections used to generate
an IV curve of a bipolar or MOS transistor. Figure 3-10
shows FET devices connected in a test fixture.
3.5.1 Test configuration
Rows A and B are used to switch the Model 237 Source Mea-
sure Unit; rows C and D are used for the Model 236.
To prevent card damage, do not exceed
the 200 volt maximum rating of the
Model 7174A when switching the Model
237, which is capable of sourcing up to
1100 volts.
At the test fixture, the drain and source leads of the FETs are
,
connected in a 4-wire sensing configuration. This connection
scheme allows the Model 237 to use remote sensing to
accurately apply Vds to the FETs. The Model 236 uses local
sensing and is used to supply the bias to the gates of the
FETs. Since the gates are low current, remote sensing is not
necessary.
If more DUT pins are needed, the system is easily expanded
by adding more Model 7174A matrix cards. Each additional
card will add 12 columns to the system.
Applications
Current Voltage
between between
F10 1-2 3-4
F10 2-1 3-4
F9 2-3 4-1
F9 3-2 4-1
F12 3-4 1-2
F12 4-3 1-2
F11 4-1 2-3
F11 1-4 2-3
CAUTION
3-9