Measurement of mechanical properties for MEMS materials

The microscopic mechanical devices in microelectromechanical systems (MEMS) use materials such as silicon and many other thin films, which had not previously been considered mechanical materials and thus are not well characterized regarding their mechanical properties. However, as the field matures, sustained research and commercial development in the coming years will demand better understanding of mechanical properties such as Young's modulus and the fracture strength. Uniaxial tension testing is generally considered the most reliable way to measure the mechanical properties. However, the problems associated with the microscopic size of the test specimen for MEMS, such as sample handling and sample alignment, led to such alternative ways as membrane-bulge testing and natural frequency testing at the beginning of MEMS. In this paper, recent methods for testing microscale mechanical properties and their results are summarized. Many reports, based on two distinct types of test, beam bending and direct tension, are introduced. The efforts to integrate the sample and loading system on the microscopic scale are also explained. Studies of fatigue, the most recent development in microscale measurement of mechanical properties, are discussed. The results from the testing methods described are listed for comparison.