Authors: J.H. Correia, M. Bartek and R.F. Wolffenbuttel
Affilation: Delft University of Technology, LN
Pages: 563 - 568
Keywords: Tenns--load-deflection, diaphragms, silicon nitride membrane, Fabry-Perot microinterferometer, LPCVD silicon nitride, residual stress, high flatness, strain.
Finite-Element-Methods (FEM) has been used to study the behavior of a non-planar composite diaphragm, which is to be used in a tunable Fabry-Perot-based silicon microinterferometer. The composite (Ag-mirrorAow-stress SiN membrane/Si-frame) diaphragm used exhibits: excellent flatness, high mechanical strength for large and thin structures, good optical properties and low-voltage electrostatic actuation. Moreover, FEM simulations show that highest stress occurs at the middle of the four outer edges of the diaphragm and maximum stress levels are below the fracture limit of the membrane. The load-deflection behavior of the (membrane/Si-frame) composite diaphragm is presented. The analysis takes into account the shape of the frame and that of the electrodes. The intluence of the frame convex corner overetch on the stress profile was also investigated. Results from FEM simulations were subsequently confirmed experimentally. Surface profilometer measurements were used to verify the load-deflection behavior of the diaphragm. The resulting error is less than 10%. This work is restricted to square diaphragms, which can be fabricated using simple bulk-micromachining.