Model 4200A-SCS Source-Measure Unit (SMU) User's Manual
Section 5: Source-measure concepts
4200A-SMU-900-01 Rev. A December 2020
5-7
Local sensing
Measurements made on devices with impedances above approximately 1 kΩ are generally made
using the local sensing method, as shown in the following figure. The SMU test current is forced
through the test leads and the DUT being measured, developing a voltage across the device (V
DUT
).
The SMU then measures the voltage across the DUT (V
M
) through the same set of test leads.
Figure 75: Local sensing
If you are measuring low-impedance DUTs, the local sensing method may give inaccurate results.
The cable resistance (R
C
) and the connection resistance (such as matrix crosspoint resistance or
prober-to-
IC pad resistance) can be as high as 1 Ω. Since the test current (I) causes a small but
significant voltage drop across the cable resistance, the voltage measured by the SMU (V
M
) will not
be exactly the same as the voltage directly across the DUT (V
DUT
) and considerable error can result.
Typical cable resistances lie in the range of 1
mΩ to 100 mΩ, so it may be difficult to get accurate
local sensing measurements with DUT resistances below 100
Ω to 1 kΩ, depending on the
magnitudes of the cable resistance and contact resistance. In these cases, you may need to use
remote sensing.
