Test & Measurement
Issue VI 2009
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Top: Figure 5: When two transmission lines are
connected in series, the characteristic
impedance of the combined transmission line is
oasiasemiconductor
the sum of the two individual transmission lines Figure 7: Connections between a DUT and an LCR/C-V meter
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Above: Figure 6: A triaxial cable
33
time it was necessary to switch to a new combination has a characteristic impedance of
measurement type. Versions of the cable kit are 50Ω. In addition, pulsing usually requires one or
available for use with probers made by Cascade more DUT pins to be connected to ground. The
Microtech probers and SUSS MicroTec. Both centre connector can be connected to the outer
versions are designed to work with a coaxial shield by adding a jumper, as shown in Figure 8,
Kelvin probe head only. to make the ground connection.
Figure 7 illustrates how a DUT can be Attaching this jumper at the end of the
connected to an LCR/C-V meter. Note that the probe arm would require disconnecting the
guard is allowed to float and the outer shields probe needle from the wafer to protect the
are all interconnected at the prober. wafer; unfortunately, the probe needle area can
(Interconnecting the outer shields does not be difficult to access. Although applying the
adversely affect I-V measurements. In some
cases, it may even improve I-V measurement
performance). The triaxial cables replace the
coaxial cables shown in Figure 2. It’s possible to
switch between I-V and C-V measurements by
re-connecting only the instrument end of the
cable. There’s also no need to disconnect the
wafer from the prober to make the switch, which
saves time and ensures consistent probe needle
to wafer contact.
Cabling for Pulse Testing
Pulse testing (as well as other test types)
requires 50Ω transmission lines to the DUT. If the
triaxial cables are designed to have a
characteristic impedance of 100Ω from their Figure 8: Pulse testing usually requires connecting one or more DUT pins
centre connectors to their outer shields and two to ground. A jumper can be used to tie the center connector to the outer
of these cables are connected in parallel, the shield to make this ground connection
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