Hi there folks,
I am tasked with building a system to test multiple on-wafer resistors (TLM structures). My post here has mostly to do with the measurement/switching part of the system. I have read a lot on the topic in recent weeks and gone through several iterations as I have learned more, but I'm new to the test side of things. I'm posting here to see if those more experienced than myself can check my work or suggest something I don't even know exists!
Here are the constraints I'm working with:
- Four wire measurements are a must
- Resistors will be as low as 0.5 Ohm and I want 3 significant figures
- I need enough channels for at least 4 resistors, so I need 4 channels of 4 pole switching minimum
- While I can spend a few thousand on this, I'm budget conscious and interested in effective options that are in the <=$1000 range even if they will take a bit more work
- I have a Keithley 2400 and a couple Agilent 34401As on hand; there are also a couple of 7001s with four pole switch cards in the lab but someone else is eyeing them too
- The equipment I use/get for this will be dedicated to this simple task, so it need not be a fancy whiz-bang-do-it-all magic box
I've formulated two general approaches to achieve this:
- 4 wire instrument with separate switch system (SMU or really any DMM paired with a low loss switch; ie Keithley 2400, Agilent 34401A for the instrument, Keithley 7001, 7002, or 702 as the switch.)
- DAQ unit that integrates DMM with multiplexing capability (ie Agilent 34970A, Keithley 199, Keithley DAQ6510)
My first question is if an integrated system is a better approach? Less loss or opportunity for interference?
My second question is what other separate switch systems exist besides the Keithleys? I've seen some older HPs on ebay, but they are very cheap and I suspect that is for a reason.
Third, I am a little skeptical of older/used equipment for this application - accuracy and precision are pretty important and I am concerned that the low upfront cost of used instruments means spending more on calibration before being able to use the thing. Thoughts?
Fourth, my inclination is that if I'm going to buy something new I may as well get an integrated system, currently leaning towards the DAQ6510. Is there a current-gen system (separate or integrated) that will meet my needs at a better value than that particular box?
Finally, here are my candidate solutions, coming from different sides of things:
- Save Time, Pay For New: buy DAQ6510
- Use What I Have, Use Extra Budget To Buy More Wafers: use Agilent 34401A and either fight for a 7001 or buy one used
I will greatly appreciate any feedback or suggestions!