Fracture of polycrystalline 3C-SiC films in microelectromechanical systems

The fracture of polycrystalline SiC films is investigated using a micrometer-sized fracture tester fabricated by micromachining techniques. A series of SiC cantilever beams varying in length are carried by a moving shuttle tethered to the substrate, and are bent in plane until fracture. The fracture strain of SiC films is calculated from the deflection of bending beams using nonlinear beam theory and determined to be 3.3%/spl plusmn/0.2%, which corresponds to a fracture stress of 23.4/spl plusmn/1.4 GPa. These values are significantly higher than those for polycrystalline silicon. In addition, the crack propagation in the polycrystalline SiC films is observed to be transgranular.