Eliminating High-Spatial-Frequency Topography due to Print-Through in MEMS Deformable Mirrors

NASArsquo;s SBIR topic S2.01 Proximity Glare Suppression for Astronomical Coronagraphynbsp;expresses specific interest in proposals for process improvements needed to improve performance of current wavefront correction devices. We propose to develop a manufacturing process for microelectromechanical deformable mirrors (MEMS DMs) that eliminates high spatial frequency topography due to print-through. In NASA#39;s extreme wavefront control systems used for space-based coronagraphy, topography needs to be at or below 1nm rms to avoid being a limiting factor in achievable dark hole contrast. High spatial frequency topography on MEMS DMs can inhibit high contrast imaging in coronagraph systems through undesired diffraction. In previous work we have developed a clear, quantitative understanding of the root causes and sources of high-spatial frequency shape errors in MEMS DMs, and have demonstrated feasibility of one promising approach to eliminate those errors. The proposed new process involves modifications of the annealing processes, sacrificial materials specifications, layer thicknesses, and processing procedures used in MEMS foundry-based fabrication of DMs, and will lead to production of DMs with surface figure errors measuring 1nm rms, about an order of magnitude lower than the current commercial state-of-the-art. We will conduct experiments on test structures to optimize topography-reducing techniques while simultaneously ensuring high yield. nbsp;By combining recent process innovations that improve topography with other recent innovations that markedly increase manufacturing yield, we will create a path toward producing ultra-smooth, high-yield MEMS DMs that will become enabling components for the space-based coronagraphs that NASA is relying on in its mission to search for habitable exoplanets.