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A G R E AT E R M E AS U R E O F CO N F I D E N C E essential to use triaxial cables for these
measurements. Figure 1 illustrates how
these measurements can be made using four
triaxial cables. The measurement signal is
carried on the center conductor, the inner
shield is driven as a guard for the signal, and
the outer shield is used for safety to shield
the user from high voltages that may be
applied to the guard and signal conductors.
Two cables are necessary in order to achieve
a remote sense, or Kelvin, connection on
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each device terminal. Remote sense cables
allow the instrument to sense the voltage
at the device accurately. In this figure, the
Measurement
device to be characterized has two terminals.
CV Measurements'
Flexibility? Cabling Requirements
Figure 2 illustrates the cabling for C-V
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measurements using four coaxial cables. The
outer shells are connected together to con-
trol the characteristic impedance the signals
More Flexible Cabling
see. The outer shells of all four cables must
be inter-connected near the device under
test (DUT).
Pulse Testing Cabling
Wayne Goeke, Senior Staff Technologist and Requirements
Lee Stauffer, Senior Staff Technologist Pulsed measurements require the highest
Keithley Instruments, Inc. bandwidth of the three measurement types,
so to prevent reflections off the DUT from
M
reflecting off the source, the cable must have
ANY different types of to the probe tips to be confusing and dif- a characteristic impedance that matches the
measurements go into ficult. This article explains the different source impedance. Pulsing does not use a
characterizing an electrical cabling requirements associated with each remote sense cable. Figure 3 illustrates a
device and the processes measurement type (Table 1) and describes a typical connection to a two-terminal DUT.
involved in its manufacture. new approach to multi-measurement cabling Pulsing is the only one of the three meas-
However, current-voltage (I-V), capacitance- that combines high signal integrity with urement types that connects the DUT to the
voltage (C-V), and pulse-based meas- excellent ease of use. outer shield of the cable.
urements are the most commonly made
measurement types in these applications. As IV Measurements' Characteristic Impedances
a result, semiconductor device characteriza- Cabling Requirements Given the challenges created by these dif-
tion systems typically include capabilities Guarding is crucial to making high integ- fering cabling requirements for different
for making these measurements, with some rity low current I-V measurements, so it's measurement types, Keithley has developed
more successful than others in integrating
these measurements in a way that reduces Table 1. Cable requirements for IV, CV, and Pulsed IV measurements.
the time and effort required to make them.
DC IV LCR/CV Pulsed IV
Perhaps the greatest challenge associated
Measurements Measurements Measurements
with integrating these measurements is the
fundamentally different cabling require-