The fourth industrial revolution – Industry 4.0 – can only succeed if the sensor systems responsible for the measurement data are further developed in parallel with data processing. Over the last few years, the industry has increasingly demanded sensors used directly on component surfaces in contact with the work piece so that local measurement data can be captured even during the process. That is why a multifunctional thin film system was developed at Fraunhofer IST for the local measurement of the pressure and temperature distribution on surfaces, for example the surface of tools. This is a wear-resistant, multi-layer system that, in addition to local force and pressure measurement on the complex shaped surface, also makes it possible to measure the local temperature and wear in the main load-carrying areas of the component – without the integration of additional measuring devices. The sensor modules can be individually designed, integrated into existing machines, or deposited directly onto 2D and 3D components with complex shapes.
The thin film system
The thin film system consists of the following functional layers precipated onto a steel base body (see opposite figure):
- A piezoresistive sensor layer (material: DiaForce®, d ~ 6 µm),
- a lithographic structured metal layer (material: chrome, d ~ 2 µm),
- an insulation and wear-protection layer (material: SICON®, d ~ 1 µm),
- a temperature meander structure (material: chrome, d ~ 0.2 µm) and
- an insulation and wer-protection layer (material: SICON®, d ~ 3 µm).
The production process
The surfaces being treated are coated by means of plasma assisted chemical vapor deposition (PACVD) with the DiaForce® piezoresistive and tribologically resistant hydrocarbon film in a thickness of 6 µm. To enable the measurement of local loads, individual circular electrode fields made of chrome are produced on the sensor layer by means of physical vapor deposition (PVD) in combination with photolithography and wet chemical etching. An insulation layer with a thickness of 1 µm is also deposited, consisting of the SICON® hydrocarbon film modified with silicon and oxygen. On this insulation layer, another chrome layer with a thickness of 0.2 µm is applied in a second PVD process. This is subsequently structured so that, on the one hand, it exhibits a meander structure used for temperature measurement. On the other hand, it contains conductive paths from the electrode structures previously produced for force measurement to the contacting area. Since the sensor structures have to be protected against wear, a final SICON® covering layer with a thickness of 3 µm is also deposited.