Compensating for atmospheric turbulence in meter-class telescopes and for free-space communications can require deformable mirrors (DM) with hundreds of actuators. Advances in high-contrast imaging techniques and increased telescope sizes require DMs mirrors with thousands of actuators [1]- [3]. In response to these needs, Iris AO has been developing a nearly 500-actuator DM and is conducting pathfinding research into 3000-actuator class DMs. This paper begins with an overview of the segmented DM design and describes improvements made to the DM over the prior year in the areas of speed, high-quality dielectric coatings, and snap-in prevention structures. The paper then describes the next-generation PTT489 DM design and fabrication process. Failure modes encountered during fabrication are presented as well as test methods to detect the failure modes. Preliminary yield data are presented for the fabrication process as well. The paper concludes with a view to the future showing pathfinding research into 3000-actuator DMs. PTT SEGMENTED DM DESIGN OVERVIEWThe Iris AO piston/tip/tilt (PTT) segmented deformable mirror (DM) is based on the PTT segment schematic diagram shown in Figure 1a. Many of these three degree of freedom segments are tiled in a hexagonally close-packed pattern to form larger arrays. A photograph of a packaged PTT111-5 DM (111-actuators, 37 PTT segments, 5 µm stroke) is shown in Figure 1b. All of the DMs manufactured by Iris AO use the same basic segment design. Therefore, all of the knowledge gained from developing the PTT111 DM design transfers to larger mirrors described herein.The MEMS DM is a hybrid of surface micromachining and bulk micromachining technologies [4] [5]. Conventional polysilicon surface micromachining technology, in this case the SUMMiT IV process, creates the actuator platform, electrodes, and underlying electrical interconnect (not shown in the schematic) shown in Figure 1a. The top layer of the bimorph flexure is added by Iris AO in order to lift the structure 20-40 µm above the substrate after release. The bimorph layer was chosen such that the coefficient of thermal expansion (CTE) is matched as close to the polysilicon as possible. * michael.helmbrecht@irisao.com, phone (510) 849-2375, www.irisao.com Electrodes Tempera ture Insensitive Bimorph Flexure Bondsites Rigid High-Qua lity Mirror Segment Actua tor Pla tform Figure 1: a) Schematic diagram of a 700 µm diameter (vertex-to-vertex) mirror segment. Scaling is highly exaggerated in the vertical direction. b) Die photograph of a 111-actuator 37-piston/tip/tilt-segment DM with 3.5 mm inscribed aperture (Product name: PTT111-5).

Iris AO has been developing microelectromechanical systems (MEMS) based deformable mirrors (DM) for a number of years. This paper presents a review of the basic segmented DM design and shows test results of a 111-actuator, 37-piston/tip/tilt (PTT) segment DM. A 489-actuator 163-PTT-segment design is described as well as progress towards the fabrication of the device. A view to the future is shown by describing path-finding research towards 3000-actuator, 1000-PTT-segment DMs.

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