Enhanced Fabrication Processes Development for High Actuator Count Deformable Mirrors

It is proposed to advance manufacturing science and technology to improve yield and optical surface figure in high actuator count, high-resolution deformable mirrors (DM) required for wavefront control in space-based high contrast imaging instruments. As the scale of batch fabricated, polysilicon surface micromachined MEMS DMs increases to thousands of actuators the associated increase in devices size limits the achievable yield due to micro-scale defects introduced during the manufacturing processes and large unpowered surface figure errors. In Phase I research, major obstacles preventing scalability of microfabrication processes to large arrays will be overcome by developing a polysilicon deposition process to reduce and control defect density to maximize the yield of a 1027 segment Tip-Tilt Piston DM with 3081 actuators and to determine the practical limits of the tool set and compatibility of this process for the manufacture of MEMS DMs with >104 actuators. Manufacturing processes to minimize unpowered surface figure errors will be developed to (1) reduce substrate curvature induced DM surface figure errors through control of deposition and polishing processes to balance the front and backside film thickness, and (2) reduce polishing induced DM surface figure errors by modifying the device wire routing layout design to maintain uniform pattern density across the device area to achieve uniform material removal rates in the polishing process. Successful completion of the Phase 1 work will enable the design and manufacture of a 1027 Tip-Tilt-Piston deformable mirror required for NASA's visible nulling coronagraph instrument in a Phase 2 effort.