From ernie@physics.carleton.ca Wed Jun 25 16:46:22 2003 Date: Fri, 20 Jun 2003 15:54:32 -0400 (EDT) From: Ernie Neuheimer To: Madhu@physics.carleton.ca Cc: Hans Mes , Kirsten Sachs , Bob Carnegie Subject: Addendum: High Resistivity Measured on Large Dimension Resistive Foils from Minesota Using the Parallel Strip Method. X-IMAPbase: 1426689743 1 Status: O X-Status: X-Keywords: X-UID: 1 Madhu, I omitted mentioning below that when we measured resistivity with the current source and the two (differential) voltmeters, we were able to measure expected resistivity, sometimes by repositioning the 4-point probe until the 100 nA source current was established. (Our current source had a voltage compliance range of about 7V whereas the Keithley 2000 has a range of about 3V.) There seems to be a contact "spreading" resistance which must be taken into account in 4-point measurements. This contact "spreading" resistance was mentioned by John Yeager of Keithley in his e-mail to me about our earlier problems with the Keithley in the 4-wire resistance mode. I will give you a copy of his e-mail and Figure 4-24 "Realistic Circuit of the Four-Point Probe Method" from the Keithley "Low Level Measurements" handbook to which he refers. For high resistance (MegOhm) four-point measurements his advice is to use separate current source (with large voltage compliance range) and a differential voltmeter. Ernie. ---------- Forwarded message ---------- Date: Fri, 20 Jun 2003 10:35:46 -0400 (EDT) From: Ernie Neuheimer To: Madhu@physics.carleton.ca Cc: Hans Mes , Kirsten Sachs , Bob Carnegie Subject: High Resistivity Measured on Large Dimension Resistive Foils from Minnesota Using the Parallel Strip Method. Madhu, As I demonstrated for you yesterday, the three foils in our possession cut from the larger sheet supplied by Astral Technology of Minnesota measured resistivity of >100, ~100.7 and ~25 MOhms per square when measured via the parallel strip method on squares of 5"x5" (two samples) and 4"x5" (third sample, quoted value adjusted for geometry). As you suggested, I re-measured the resistivity on sample 1 with contact to the resistive foil made by strips of spray-on nickel coating. The measured 80 MOhms per square is consistent with the earlier measurement and the fact that our "masking" left a lot to be desired as some conductive spray coated the foil surface. When held against a bright halogen light, the foils showed noticeable long, curved lines which could be in the deposited resistive coating. The smaller sample showed fewer such lines. This results and finding could explain the widely varying, poor repeatability and even out of measurement compliance results we have had with the 4-point probe, cylindrical probe and 100 nA independent current source/voltage methods of measurement. I have ordered the 1 mil and 2 mil rolls of Mylar type A (un- coated) polyester film from GE Polymershapes and these should be in this Thursday. You have sheets of the 2 mil Mylar foil found in the lab and sheets of the 3 mil matte finish Mylar from Loomis and Toles. It seems to me that a more reliable conductive foil is one which the conductive layer is intrinsic to the foil and not subject to damage on the surface. The ~75 nm deep conductive layer induced in films by ion beam exposure, such as mentioned in the Korean paper I showed you, is what I mean. Ernie.