Improved comb drive design for MEMS piston mirror arrays

MEMS (micro electro mechanical system) based piston mirror arrays are key elements for real time computer generated holograms (CGH) in visualisation technologies like virtual, augmented and mixed reality (VR/AR/MR). The EU funded Project REALHOLO is developing a spatial light modulator (SLM) that is based on comb drive MEMS actuators that can fulfil the tight requirements of the optical and mechanical performance and the high level of integration. A previous design already outlined perspectives for a superior performance in comparison to other approaches for high frequency and high precision wave front modulation, but has restrictions due to the resolution and feature size of the i-line lithography system used for manufacturing. This paper discusses the optimisation of the design applying an advanced manufacturing process using DUV lithography that allows smaller features and therefore offers additional design options. By introducing an improved comb drive geometry the electrostatic force was significantly increased, which allowed the optimisation of other geometries, like horizontal and vertical gaps and additional shielding structures, for an even more linear actuator response and reduced crosstalk. The electrostatic and structural FEM simulations will show the significant improvements in overall performance, compared to the previous iteration and other types of SLMs. The improved actuator can potentially extend the field of application from the desired automotive driver assistance holographic 3D display to head mounted displays for VR, AR and MR applications as well as other technologies like material processing.