Development of Stress Relief Suspensions for Micro-Machined Silicon Membranes
A new design concept for large (6 mm diameter) dynamically focusing silicon membrane mirrors using electrostatic actuation was realized. With this concept membrane buckling by residual compressive stress inside the membrane can be avoided. To eliminate the influence of residual stress (compressive or tensile) a membrane suspension with a novel stress relief design was developed by the use of finite element simulations. The improvement was achieved by a special tangential beam suspension, which allows an in-plane expansion or contraction of the membrane, which reduces the stress induced out-of-plane deformation and leads to substantially flat and distortion-free micro mirrors (distortion < λ/10). Measurements of realized devices are in very good agreement with the prediction of the FEM simulation.