Deposition of piezoresistive films for strain gauge application using an industrial high-rate inline sputtering system

Nowadays sputtered strain gauges are widely used e.g. in high precision pressure sensors. Special highly sensitive piezoresistive nano-composite films consisting of metal nano particles embedded in an insulating diamond-like carbon (DLC) matrix can lead to further measurement accuracy. Important parameters for characterizing the film properties are the strain sensitivity (described by the gauge factor GF) and the temperature coefficient of resistance (TCR). The gauge factor of conventionally used NiCr based alloys does not exceed a value of 2. Metal containing DLC films have already reached 5 to 10 times higher strain sensitivity on laboratory scale in combination with a TCR close to zero. First, static deposition in a box coater was used to produce the highly sensitive films which resulted in quite long process duration. By using a dynamic process in the same coating system the throughput of samples was slightly increased. For using these films on industrial scale much higher efficiency was necessary and therefore, the process was transferred to an industrial high-rate inline sputtering system. By gaining the same sensitivity as in the dynamic process in the box coater a more than 20 times higher throughput was realized by using this new sputtering system. The used kind of sputtering system is also commercially available with enlarged process chambers and offers the possibility to transfer the process efficiently on industrial scale.