Mechanical Properties of Near-Frictionless Hydrogenated Amorphous Carbon Freestanding Thin Films for MEMS Devices

Abstract

Diamond-Like carbon (DLC) films with a mixture of sp2 and sp3 hybridizations have exhibited excellent properties such as chemical stability, wear resistance, optical transparency and are now widely used as protective overcoatings in various fields. In this paper, the membrane deflection experiment (MDE) was used for measuring the Young’s modulus, fracture strength, and residual stress of the so-called Near-frictionless carbon (NFC) films developed at Argonne National Laboratory. In this method, free standing NFC membranes were fabricated and stretched by a nanoindenter while deflection was monitored with an interferometer. By combining these two independent measurements, the mechanical properties of NFC films were characterized. The specific a-C:H films were grown at Argonne National Lab and are those films that exhibited excellent tribological properties with super low friction coefficients of 0.002. The Young’s modulus of NFC films measured from 45 membranes ranged from 32 GPa to 38 GPa. The average (arithmetic mean) value was 35.13 GPa. The standard deviation was 2.292 GPa. The fracture strength varied from 0.12 GPa to 0.90 GPa and the residual stress ranged from 79 MPa to 310 MPa. Width and thickness effects of the membranes were also studied in this work. It was found the fracture strength increased with decreasing membrane width and thickness. The residual stress increased with decreasing membrane thickness.