# 4T sensing question

1. Sep 29, 2010

### guusmatijs

I am currently working on printing conducting inks. After printing and sintering the inks my goal is to measure conductivity of my printed patterns. Therefore I want to create 4 strips of aluminium using deposition on my substrates before I print my ink.
I want to use these strips to perform a four terminal sensing measurement on the conductivity of my printed ink strips. In most documentation I find that the distance between points 1-2 and 3-4 in the image below is smaller than the distance between points 2-3.

However the mask I created for depositing the aluminium on my substrates leaves four strips of aluminium with equal distances (see image below) 10 mm from center to center.
[PLAIN]http://image.bayimg.com/hapbaaach.jpg [Broken]
the strips of aluminium left on the substrate will have a width of 1.5 mm.

The actual question is whether I can use R=U/I, simply ohms law, or whether I need to use a correction factor like discussed in Haldor (please refer to attachment), R=G * U/I.

The strips I will be printing across the aluminium strips will have a width of 100-1000$$\mu$$m depending on my printing settings. the thickness of my print will be approx 10 times smaller.

I hope I cleared out my question, If you need anything else please let me know.

Thank you :)

Attachment: Haldor
http://dl.dropbox.com/u/1073056/Handige%20eBooks/Haldor%20weerstandsbepaling.pdf" [Broken]

Last edited by a moderator: May 4, 2017
2. Sep 30, 2010

### MATLABdude

Welcome to PhysicsForums!

My expertise in 4 Point Probe Measurement technique is rather limited, however, I believe that you may have some problems with the fact that the probe contact area looks to be rather extensive. Depending on deposition technique and process conditions, you may also need to factor in the resistance of the aluminum probes themselves.

Given that these seem to be rather large samples, could you just use a stand-alone 4 point probe (with, say, 0.25 to 1 mm spacing) instead of embedding electrodes? It'd also reduce your per-sample cost (if that's at all a concern).

If you can get a copy, the reference I have in my notes from my Thin Films class is Mott and Davis' Electronic Processes in Non-Crystalline Materials (even if it's from 1979).