Measurement of the mechanical properties of electroplated gold thin films using micromachined beam structures

Abstract

We have measured the Young's modulus, residual stress, and stress gradient of electroplated gold thin films using surface micromachined beam structures. Cantilever and bridge beam structures of different lengths were fabricated using UV-LIGA surface micromachining and dry-release methods. The Young's modulus and residual stress of the fabricated beams were determined from the resonance frequencies of electrostatically excited beams, and the stress gradient was evaluated from the self-deformation of released cantilevers. The observed Young's modulus was smaller than the bulk Young's modulus, and showed small changes depending on the deposition current density. The average residual stress was found to be tensile in nature, and the observed residual stresses showed no differences, regardless of the current density. However, the stress gradient increased with increasing current density. The deformation of the cantilever beam after release was dependent on the plasma ashing time used. This result implies that additional thermal effects from the post-deposition process may have an influence on the final performance of fabricated micro electro mechanical systems (MEMS) devices. (C) 2004 Elsevier B.V. All rights reserved.