Comparison of techniques for measurement of residual stresses in multilayered micro-electro-mechanical devices

A major concern in the development of microelectromechanical systems (MEMS) is the presence of residual stress. Residual stress, which is produced during the fabrication of multi-layer thin-film structures, can significantly affect the performance of micro-scale devices. Though experimental measurement techniques are accurate, actual stress measurements can vary dramatically from run to run and wafer to wafer. For this reason, the modeling of this stress can be a challenging task. Past work has often focused on experimental, static techniques for determining residual stress levels in single-layer and bi-layer structures. In addition, these past studies have concentrated on residual stress measurements in thin films as they are being deposited and prior to the release of a particular device. In this effort, three techniques are used for determining residual stress levels in four-layer piezoelectrically driven cantilevers and resonator structures. The first technique is a static technique that is based on wafer bow measurements and Stoney's formula. The second technique is a dynamic technique that is based on parameter identification from nonlinear frequency-response data. The third technique is also a static technique based on parameter identification from static device deflection measurements. The devices studied, which are piezoelectric devices, are fabricated with varying lengths and widths. The results obtained from these three techniques will be compared and discussed, and it is expected that this work will enable the characterization of residual stress in micro-structures after they have been released.