Micron-scale Al Particulates to Improve the Piezoresistive Performance of Amorphous Carbon Films

Amorphous carbon (a-C) has been extensively studied as a promising candidate for microelectromechanical system (MEMS) piezoresistive sensors owing to its excellent mechanical properties and sensitivity. However, the semiconductor features of a-C films complicate achieving a high gauge factor (GF) and low temperature coefficient of resistance (TCR). In this study, we introduced micron-scale Al particulates (2.4-5.2 mu m average size) by dewetting before a-C deposition, which simultaneously improved the GF and reduced the TCR of the composite structure. An atomic bond analysis revealed that applying the Al particulates favored the formation of sp2, thus reducing the localized surface potential of the a-C film. When the density of the Al particulates reached 15,000/ mm2, the GF (36.9) of the a-C film significantly increased by more than 350 %, whereas the TCR decreased as the average size of the Al particulates increased. Furthermore, the composite exhibited typical Schottky contact characteristics and formed a Schottky barrier of 0.43 eV at the Al/a-C contact interface. Carrier transport between the Schottky barriers was achieved by the holes (primary carriers) via tunnelling. These significant piezoresistive properties can be explained by the variation in the Schottky barrier height.