Stress Optimization for a MEMS Multilayer Fixed-Fixed Beam

Micro-Electro Mechanical System (MEMS) based multi-layer fixed-fixed beams are used as suspensions to support the suspended membranes in tunable Fabry-Pérot Filters and tunable Vertical Cavity Surface Emitting Lasers. The electrical and optical performance of these devices depends highly on the parallelism of the suspensions holding the membrane in place. However, the residual stress in the suspension layer(s), upon relaxation, results in bending of the suspensions, which in turn results in displacement of the membrane. Therefore, the stress induced bending in the free-standing suspensions holding the membrane in place, must be minimized. A novel stress optimized multi-layer suspension system consisting of a fixed-fixed beam is designed in this work, whereby a tensile stressed material is sandwiched between two compressively stressed material films; such that the suspension layer system has an overall tensile film force, while an additional stress less layer is used to balance the clock-wise and counter clock-wise moments. The displacement of the central portion of the fixed-fixed beam is reduced from several micrometers to a mere 1.63 nm using this technique.