AVS 46th International Symposium
    Thin Films Division Wednesday Sessions
       Session TF+MM-WeM

Paper TF+MM-WeM6
Residual Stresses in MEMS Structures

Wednesday, October 27, 1999, 10:00 am, Room 615

Session: Thin Films in MEMS and MOEMS
Presenter: B.S. Majumdar, UES, Inc.
Authors: B.S. Majumdar, UES, Inc.
W.D. Cowan, Air Force Research Laboratories
S. Rogers, AFIT
N.J. Pagano, Air Force Research Laboratories
Correspondent: Click to Email
Residual stresses impose major restrictions on the performance of MEMS devices. Although different techniques have been developed to measure such stresses, they suffer from a number of limitations. We have focused our attention on square and circular micro-mirrors that are supported by electrically activated arms. Permanent curvature in such mirrors arise from thermal and process-generated residual stresses, and they seriously impair mirror performance. In this work, the residual stresses were estimated from curvature measurements on different sized beams using an interferometric technique, complemented by rigorous elastic analysis of composite beams. It is notable that typical analyses is based on Stoney's equation, which is not believed to be valid for the thin MEMS structures. The composite beams consisted of different grades of poly-silicon with and without gold coating, and the measurements and analysis showed consistent results for the different beams and mirrors. In an effort to de-couple the thermal and process component of the residual stresses, curvature measurements were made at different temperatures. The results and analysis technique will be presented in detail, and possible methods to reduce the residual stresses will be discussed.