Abstract
New sensor and sensor manufacturing technologies are identified as a key factor for a successful digitalisation and are therefore economically important for manufacturers and industry. To address various requirements, a new sputter coating system has been invented at the Institute of Micro Production Technology. It enables the deposition of sensor systems directly onto technical surfaces. Compared to commercially available systems, it has no spatial limitations concerning the maximum coatable component size. Moreover, it enables a simultaneous structuring of deposited layers. Within this paper, characterisation techniques, results and challenges concerning directly deposited thin film strain gauges with the new sputter coating system are presented. Constantan (CuNiMn 54/45/1) and NiCr 80/20 are used as sensor materials. The initial resistance, temperature coefficient of resistance and gauge factor/k-factor of quarter-bridge strain gauges are characterised. The influence of a protective layer on sensor behaviour and layer adhesion is investigated as well. Moreover, the temperature compensation quality of directly deposited half-bridge strain gauges is evaluated, optimised with an external trimming technology and benchmarked against commercial strain gauges. Finally, the suitability for high-temperature strain measurement is investigated. Results show a maximum operation temperature of at least 400 °C, which is above the current state-of-the-art of commercial foil-based metal strain gauges.
Highlights
Strain gauges are used as universal measuring devices for detecting mechanical strain within technical components
The temperature behaviour of such strain gauges is described by the temperature coefficient of resistance (TCR) (Equation (1))
Manufacturing of Constantan and NiCr 80/20 layers takes place with a power of 200 W, an argon flux of 7.5 sccm and a sputter pressure of of 15 approximately 6.8 × 10−3 mbar. Both sensor materials are chosen as they enable a low TCR3 that simplifies temperature compensation and features a sufficient k-factor
Summary
Strain gauges are used as universal measuring devices for detecting mechanical strain within technical components. A metal strain gauge consists of at least one meander-shaped sensor structure on a thin carrier substrate, for example a few ten micrometre thin polyimide foil, contact pads and a protecting top layer [2]. Such strain gauges are glued onto the surface of a component. Deposited strain gauges are manufactured in commercial vacuum coating systems [8,12] Such systems feature a vacuum chamber of limited size resulting in restrictions concerning the maximum dimensions of the coatable components. The system setup and manufacturing features, where the component to be coated becomes one part of the chamber, is related to pending [16,17] and granted patents [18]
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