I-V characteristics of coated membranes
I measured the I-V characteristics of our coated membranes
on Wed. at RIT. JP observed the measurement.
The semicon parameter analyzer in the test lab is "old" but is
exactly what we need! Roughly speaking, our coated membranes
have resistance about 2k Ohm, depending on the thicknesses of
metal films (this is based on pure Ti coated samples, not Ti+Au).
The I-V curve is linear since we are probing on metal films, not
M-S contact.
I didn't collect raw data in terms of data sheet at this time,
because Dr. Karl was not available to show me how to use the
PC based software. So I just manually measured our samples
using the parameter analyzer. But I did take photos of the I-V
curves and derived the resistance of the membranes with
metal coating. Next time I should be able to collect raw data
from the measurement.
short probes (note the 100mA compliance)
bare Si (note the scale is nA)
20nm Ti coated membrane (note abt 1mA@2V)
30nm Ti coated membrane (note abt 1.35mA@2V)
I can present the data in our group meeting next week. We
can discuss these data after I explain these results.
Lingyun,
Were these plots made with a two-point probe?
The 20nm Ti film looks to have a “resistance” of 2kohm. Is this what we expected? Seems high to me… What was the distance between the probes? Do you think it’s possible we’re not getting a continuous layer of metal based on this measurement?
Something to keep in mind (mentioned by Chris at last week’s meeting): Based on the plot with the probes shorted (100mA @ 0.5V), the “contact resistance” of the probes is ~5ohm. With the two point probe, you’re limited by this resistance. In other words, we can’t measure highly conductive materials with this setup.
Hopefully we can make the four-point system accept our membrane format (or vice versa)!
As long as the films have such poor conductance, the 2-point measurement should at least allow for some experimental optimization. Nothing will be publishable until a 4-point measurement system is used.
I’m concerned about 2 things with these measurements:
1) contact resistance – how do you know that you are measuring the film and not just the contact points. (much less of a concern in a 4-point setup)
2) Ti oxidizes in the air – how do you know that you are measuring a film of Ti, not TiO2? Why was a gold film not measured?
Have you made any samples with Ti+Au WITHOUT breaking vacuum, as I suggested over 1 month ago? I have not seen any images from this experiment yet.
Funding for this project goes through May, if I remember, and the metalization was just one of the goals – we need to pick up the pace and devote more resources if necessary! We still need to design the diffusion cell that will allow the membrane to be biased….