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Model 4200-SCS Reference Manual
Performance of an integrated semiconductor test system
When performing a semiconductor I-V measurement, there will always be a speed-noise trade-off.
Even with given measurement settings, changing the system configuration (such as cable length
or adding a switch matrix) will change the measurement results. The 4200-SCS has four settings
to allow optimal I-V measurements. There are three fixed settings: fast, normal, and quiet. In
addition, there is a custom setting to allow the measurement parameters to be customized.
To achieve a low-noise measurement, the quiet setting is recommended. The trade-off is that
measurement speed will be lower in comparison to the fast and normal settings. To make a fast
measurement, the fast setting can be selected, though the noise will be higher. Typically, the
normal setting is used to balance the speed and low-noise requirements. To further fine-tune the
measurement, the custom setting can be used.
The fast/normal/quiet settings are tuned to the 4200-SCS for a standard length of cables
connected to the DUT. In general, this should be sufficient to make good measurements. However,
when extra long cables and/or a switch matrix are used in the system, these settings may not be
adequate. A typical phenomenon will be the appearance of a glitch or offset error. The magnitude
of the error increases if the fast setting is used to make the measurement. This is caused by
insufficient settling time for the system. With added load or capacitance (cables or matrix relays), it
will take longer to let transient effects settle. Using the measurement parameters optimized for
short cables only may result in an erroneous measurement.
The best way to minimize this effect is to allow extra settling time. The normal or quiet settings
should improve the measurement result. Custom can also be used to fine-tune the measurement
settings; this may be a trial and error process. Various combinations of parameters can be used to
achieve the best results. In general, longer cables or slower settling of switch relays will require a
larger delay factor.
Interference
Various forms of interference that can degrade measurement integrity include:
Electrostatic interference
Electrostatic interference occurs when an electrically charged object is brought near an uncharged
object, thus inducing a charge on the previously uncharged object. Usually the effects of such
electrostatic action are not noticeable because low impedance levels allow the induced charge to
dissipate quickly. However, the high impedance levels of many SMU or preamp measurements do
not allow these charges to decay rapidly, and erroneous or unstable readings may be caused in
the following ways:
4200-901-01 Rev. S / May 2017
•
Electrostatic interference
•
Radio frequency interference
•
Ground loops
•
DC electrostatic fields can cause undetected errors or noise in the reading.
•
AC electrostatic fields can cause errors by driving the amplifier into saturation, or through
rectification that produces DC errors.
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Section Topics
Section 5: Source-Measure Concepts
5-25
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