Lately I'm having a problem of measuring low R devices with high R leads using PXI-4132 SMU.
Here is my situation: I have on-chip devices that have on-chip resistors as well. I need to do 4 point measurements on this devices to exclude leads contribution to resistance. The problem is that devices are aroung 50 Ohm and leads are 5k-100kOhm. In particular I have the following circuit: Hi and Lo pins of SMU are connected to devices through 7kOhm resistor in series (Hi - 7k -(connection to sense)- device -(connection to sense)- Low) and I'm measuring voltage on remote High/low across device but have 100k lead resistance. (RemoteHigh - 100k - (connection to Ibias lead) - device - (connection to I bias lead) - remoteLow)
I have 100uA bias current, 10V voltage range/voltage limit, SMU not in compliance but I'm still measuring around 7k instead of 50Ohm.
Is there any way to perform these type of measurements or it's outside of SMU "comfort zone"? I do understand that voltage drop across leads getting close to spec 1Vmax, but what is actually limiting the max leads resistance values for PXI SMUs?
Another piece of the puzzle: in PXI DMM max 4point wire lead resistance should be within 10% of the current resistance range. I assume the same should be applicable to SMU as well. Hence, for 100uA current range and 10V voltage range what will be corresponding "resistance" range? Is it current resolution limit?