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Development of Me-DLC films for strain gauge applications

: Bandorf, R.; Heckmann, U.; Lübke, M.; Schnabel, S.; Bräuer, G.

Society of Vacuum Coaters -SVC-, Albuquerque/NM:
Society of Vacuum Coaters. 52nd Annual Technical Conference 2009. Proceedings : May 9-14, 2009, Santa Clara, CA USA
Albuquerque: SVC, 2009
ISBN: 978-1-878068-29-3
Society of Vacuum Coaters (Annual Technical Conference) <52, 2009, Santa Clara/Calif.>
Fraunhofer IST ()

In many industrial applications strain gauges are used for measurement of applied forces or the loading status of work pieces. Humidity and temperature can cause measurement errors of common strain gauges due to creep and swelling when these use polyimide foils. Such problems can be avoided by direct application of this strain gauges on the work piece surface. Besides the improved signal the gauge factor can be further improved by using new sensor materials.
A high gauge factor of up to 1000 for diamond-like carbon (DLC) films can be found in many publications. Unfortunately, a very high negative temperature coefficient of resistance (TCR) is also connected with those properties. By adding metal which has a positive TCR to the DLC a thermal compensation can be realised. For the investigation of suited materials for thermal compensated strain gauges with a gauge factor higher than 2, which is found for conventional NiCr, DLC films were doped with different metals (Ti, W, Ni) and the resulting sensor properties were characterised. While Ti- and W-DLC always showed a positive TCR, for Ni-DLC zero crossing of the TCR was observed depending on the metal content. The gauge factor of those Ni-DLC films was higher than 10, resulting in a significant increase in sensitivity with the potential for thermal compensation.