NiC: a highly sensitive functional layer based on a nickel/graphene thin film for pressure and force sensors.

Abstract

A functional layer based on nickel and graphene called NiC was developed with the goal of a high strain sensitivity in combination with an adjustable temperature coefficient of resistance (TCR). A gauge factor up to 30 and TCR values of approximately 0±25 ppm/K can be achieved by variation of the film composition. Based on the increased sensitivity the important pressure range of below 2.5 bar is opened up for steel membrane pressure sensors without the need of a sophisticated technical effort. First pressure and force sensors with NiC functional layers were realized in order to demonstrate the high performance of this new material. The enlarged sensitivity of the film leads to a complex re-development of the microsystems “pressure and force sensors” in order to take the advantage of the high linearity, low hysteresis, high overload protection and stability. Due to the high sensitivity, it is possible to produce sensors with significantly increased stability values in the overload region. Using the same output voltage range as usual with NiCr thin film elements, the overload capability of the sensors with the new functional layer is about twenty times the characteristic value of NiCr sensors. On the other hand, the low pressure range is opened up since the membrane needs to be deformed only one tenth of its usual value. Because of this low stress the load cycle stability increases accordingly. Additionally base body materials like 1.4435 (316L), which are not very suitable for the production of pressure sensor membranes, can be used for example for hydrogen applications.