Kelvin Probe <-> 4 point Probe

Discussion in 'Homework Help' started by Peter2, May 9, 2008.

  1. Peter2

    Thread Starter New Member

    May 9, 2008
    I'm new here and my english is also not very good, but I hope I can articulate my question anyway.
    I have the agilent 4155C Semiconductor Analyzer. This one dosen't allow Kelvin probe measurements. the 4156 does. I know that the 4156 has two terminals for each SMU, one as force and one as sens I guess?
    But why is it not possible to do a Kelvin probe with 2 SMU's from 4155 as current source and the other two as voltmeter?
    In an Keithley Low level Measurement Handbook I read the four point probe (don't they actually mean Kelvin probe?) gets influenced by an AC current that flows from the LO terminal of the current source through the sample to the LO term of the voltmeter.
    Then they explain how you can prevent this, using two electrometers and two buffers. (Figure 4-27 if anyone has the handbook, if not I will try to post the picture)

    I also heard about the 4 point probe, but couldn't understand what's the difference between Kelvin and four point probe.
    And if there is any, is it possible with the 4155C?
    Thank you very much for your efforts,