Generated Currents - Keithley 4200A-SCS Reference Manual

Section 12: Maintenance

Generated currents

Any extraneous generated currents in the test system add to the expected current, which can cause
errors. Currents can be internally generated, as in the case of preamplifier input offset current, or they
can come from external sources such as insulators and cables. The following paragraphs discuss the
various types of generated currents. The next table summarizes the typical ranges of a number of
generated currents.
Typical generated currents
Effect
Triboelectric
Mechanical stress (Teflon)
Mechanical stress (ceramics)
Clean epoxy circuit board
Dirty epoxy circuit board
Offset currents
The preamplifier has a small current, known as the input offset current, that flows at all times. As
shown in the figure below, the input offset current adds to the measured current so that the SMU
measures the sum of the two currents. Note that input offset current can be brought to within
specifications by calibrating the system. Refer to
Offset currents can also be generated externally from such sources as
and piezoelectric effects
adds to the source current, and the SMU again measures the sum of the two. These external offset
currents can be suppressed manually by subtracting them using the Formulator or the Calc
worksheet. For more information, refer to
Run tab.
12-12
Model 4200A-SCS Parameter Analyzer Reference Manual
Generated current range
1 fA to 10 nA
1 fA to 1 pA
100 aA to 100 fA
100 fA
100 pA
Calibrate the system
Figure 495: Input offset currents
(on page 12-13). As shown in the next figure, the external offset current also
The Formulator
(on page 12-5).
triboelectric
(on page 6-222) and Analyze data using the
4200A-901-01 Rev. C / February 2017
(on page 12-13)