Novel applications of piezoresistive thin film systems based on hydrogenated carbon

Thin film sensor systems based on hydrogenated carbon have the advantage to combine two very important characteristics. They show a piezoresistive behaviour and also a tribological stability caused by a high hardness and wear resistance. Therefore they can be applied on the surface of machine parts or used for building up universal insertable sensor systems like sensory washers. A real challenge is the deposition of a whole sensory layer system on technical components like a spindle, which have a length of 480 mm and an outer diameter of about 90 mm. The functions of the layer system directly applied in the contact zone between spindle shaft and tool holder are the measurement of the clamping force of the tool holder, the imbalance of the used tool and the process forces during machining. For this application a self-contained thin film sensor system is investigated. Directly in the spindle shaft an insulating alumina layer is deposited in a thickness of about 4 µm followed by electrode structures out of 200 nm thin chromium coating. On top of this the piezoresistive hydrogenated carbon layer in a thickness of about 1 µm is deposited, covered by a wear resistant and insulating top coating. Therefore a silicon and oxygen modified carbon layer in a thickness of about 2 µm is used. The piezoresistive sensor layer and also the top layer are part of the diamond like carbon layer family [1,2,3,4]. Another very important application is the sensory washer. The thin film sensor system, consisting out of the piezoresistive sensor layer deposited directly on the washer surface, the electrode structures out of chromium for the local detection of the load distribution in the washer system and the insulating layer as top layer out of the silicon and oxygen modified carbon layer, has a thickness in the range of 9 µm. In the latest investigations this layer system is connected with a RFID-chip for contactless data transmission.