FEM Simulations to optimize a micro mirror array package for a wide operating temperature range

The package of a Micro-Opto-Electro-Mechanical System (MOEMS), a Micro Mirror Array (MMA) based Spatial Light Modulator (SLM), has to stay stable over the full operation temperature range and throughout SLM lifetime in spite of the inevitably different coefficients of thermal expansion (CTE) of the various materials involved. Additionally, in our case the window not only protects the MMA from mechanical damage and corrosion but also serves an optical function as part of a beam combiner. Within the European Union funded Project REALHOLO we are therefore developing a packaging concept that accomplishes the desired optical functionality while meeting the challenge of precise alignment of the window relative to the micro mirrors in lateral direction, which is the motivating factor behind the FEM simulations presented here. The objective of this research is to stabilize the package when subjected to temperature changes by simulating its thermomechanical behaviour with Ansys WorkbenchTM. A heatsink, a silicon crystal-based MEMS chip, and a window are glued together to form the package. Materials used for window and heatsink components, respectively, are chosen for a best possible CTE match. The significant parameters to be considered for package optimization are the misalignment between window and chip, the stress induced in the package, especially the glue, and the global deformation of the MMA surface. This paper discusses the challenges and possible solution based on a series of simulation findings.