Novel measurement method of internal stress in thin films using micro spring structure

Abstract

Micro-Electro-Mechanical Systems (MEMS) devices are fabricated using various materials such as silicon-based materials (Petersen, 1982). Among them, monocrystalline silicon and polycrystalline silicon are suitable materials for MEMS due to their superior strength and elasticity (Johansson et al., 1988). However, as more advanced functions and performance are demanded of MEMS, Si-based materials alone are no longer sufficient to meet these requirements. Therefore, amorphous alloys are often used in MEMS as materials with mechanical properties superior to those of Sibased materials (Saotome et al., 1998).In general, amorphous alloys are difficult to form because they are formed by melting the material and cooling it above a critical cooling rate of about 106 K/s. Thin film metallic glasses, a type of amorphous alloy thin film, have a critical cooling rate of 10-2 to 10-1 K/s at the lowest level depending on the composition, and it has been reported that an amorphous phase can be obtained more easily than in general amorphous alloys (Inoue, 2001). Therefore, thin film metallic glasses are suitable new materials for MEMS from the viewpoint of amorphous phase forming ability and mechanical properties.When thin film metallic glasses are applied to MEMS, it is necessary to establish microfabrication techniques and control internal stresses in the same way as for Si-based thin film materials (Yamadera, 1999). Sputtering is applicable