Section 6: Optimizing SMU measurements
Model 4200A-SCS Source-Measure Unit (SMU) User's Manual
6-4
4200A-SMU-900-01 Rev. A December 2020
To avoid oscillations for a FET, try the following actions:
•
Set (Drain SMU current measure range) = (Source SMU current measure range)
•
If necessary, set both SMUs to autorange.
•
Configure the source SMU for the Voltage Bias Operation Mode and set it to 0 V. This allows you
to configure the current measurement range.
For the source SMU, do not select the Common Operation Mode. This mode prevents you from
configuring a current measurement range for the source SMU. This results in a lower impedance than
at the drain SMU, a potentially high gain, and an increased likelihood of low-frequency oscillation.
To avoid oscillations for a BJT, try the following actions:
•
Set (Collector SMU current measure range) = (Emitter SMU current measure range)
•
If necessary, set both SMUs to autorange.
•
Configure the emitter SMU for the Voltage Bias Operation Mode and set it to 0 V. This allows you
to configure the current measurement range.
For the emitter SMU, do not select the Common Operation Mode. This mode prevents you from
configuring a current measurement range for the emitter SMU. This results in a lower impedance than
at the collector SMU, a potentially high gain, and an increased likelihood of low-frequency oscillation.
Both the Drain/Collector and Source/Emitter (SMU) must be set to measure current if they are set to
autorange.
Low-current measurements
Low-current measurements made with a SMU or preamplifier are subject to error sources that can
have a serious impact on measurement accuracy. The following topics discuss low-current
measurement considerations, including leakage currents, generated currents, noise and source
impedance, and voltage burden. Refer to the Keithley Instruments
Low Level Measurements
Handbook
for more information. The
Handbook
is available in the Learning Center.
