Silicon incorporated amorphous carbon films for BioMEMS application

Abstract

Amorphous carbon (a-C) or most commonly known as diamond-like carbon (DLC) is traditionally used as a protective or passivation coatings. The prospect of a-C, specifically low stress or stress free film for use in microelectromechanical systems (MEMS) has stirred up quite an interest in the scientific community. In the asdeposited state, the material exhibits extremely high compressive stress. In order for the micromachined structures to work, the films must have very low stress and very low stress gradients. Preliminary studies have shown Si doping not only reduces the stress, it can improve the haemocompatibility of a-C as well. Therefore, Si doped a-C is suitable for MEMS devices in medical applications. Amorphous carbon containing Si (a-C(Si)) exhibits some very desirable characteristics. However, many concerns (mechanical, biological and microfabrication) are still unaddressed, and the fundamentals of the current research findings are still unclear. In order to understand this material and for its successful incorporation into biomedical MEMS devices, the influences of Si incorporation into a-C network are studied in detail in this project. Amorphous carbon films containing different concentration of Si are deposited via magnetron sputtering of graphite and Si targets. Atomic bonding configurations are analyzed, and their influences on the mechanical and biological properties are studied. The best a-C(Si) in terms of its bonding and mechanical characteristics is selected to undergo thermal treatment in order to further study the temperature effect on the various properties and behaviors. The incorporation of Si into the a-C network alters the atomic bonding configurations. C-Si sp 3 bonds form through breaking up C=C sp 2 aromatic ring bonding structures. Therefore, with increasing Si, C-Si bond concentration increases while that of C=C bond decreases, and the concentration of CC sp 3 is not affected. Amorphous carbon film containing ~37at.% Si is found to have the highest sp 3 bonding fraction. Post-deposition annealing of a-C(Si37.6at.%) shows