Section 3: Source-measure hardware
Model 4200A-SCS Parameter Analyzer Reference Manual
3-28
4200A-901-01 Rev. C / February 2017
Sense selection
The sensing method is automatically selected depending on the connection method used. To use
local sensing, connect only SMU FORCE and ground unit FORCE (COMMON) to the DUT (see
previous figure "Local Sensing"). To use remote sensing, add the SENSE connections shown in the
previous figure "Remote Sensing."
Local sensing
Measurements made on devices wit
h impedances above approximately 1 kΩ are generally made
using the local sensing method, as shown in the next 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.
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.
Figure 63: Local sensing
