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High-Performance MEMS-Based Deformable Mirrors for Adaptive Optics Iris AO, Inc. Iris AO Inc. Founded in 2002 Small high-technology firm specializing in AO Aim to build high-performance, robust MEMS based DMs that address a large application space
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High-Performance MEMS-Based Deformable Mirrors for Adaptive Optics Iris AO, Inc.
Iris AO Inc • Founded in 2002 • Small high-technology firm specializing in AO • Aim to build high-performance, robust MEMS based DMs that address a large application space • Funded by SBIR grants, CfAO grants, consulting and driver / DM sales
Iris AO Segmented MEMS DM • Robust assembled mirror surface stays flat • Temperature insensitive bimorphs elevate mirror above substrate • Piston/tip/tilt electrostatic actuation
Electrostatic DM Actuators • Actuators wired to periphery • Electrostatic forces pull actuators down • No hysteresis • 4.2 mm aperture • Engineered stresses create beam shape • Stroke determined by design, not process
Assembled SOI Mirrors: Benefits • Single crystal mirror has excellent flatness • Thickness gives rigidity • Mirror is still flat after optical coating • Stays flat over varying operating conditions • Temperature • Actuation • High fill factor • Mirrors cover bimorph flexures • Etch holes not necessary
DM Stroke: Position vs. Voltage • Nonlinear position • Very repeatable
Surface Figure vs. Temperature • Optical coating on the DMs forms a bimorph that deforms with change in temperature • Some coating stacks have shown to reduce stress mismatches • These stacks do NOT help when materials plastically deform • Best coating for MEMS used for MIR is Au • Au plastically deforms at >~100MPa
Bimorph-Flexure Benefits • Stroke (gap) dictated by design, not process • Simple design with a lot of latitude for design changes • Materials chosen to minimize deflection vs. temperature • Position vs. Temperature = ~2nm/°C • Film non-uniformity across 6” wafer < ~5% • Non-uniformity across chip < 1% • Differences in height due to temperature swings are minimal
Electrostatic Actuation • No hysteresis • Nonlinear with Voltage • Highly repeatable • Temperature independent • Often high-voltages involved (200V) • High voltage is a potential reliability problem • Electrode erosion • Dielectric breakdown • Leakage currents • Dielectric charging • Iris AO DMs operate over 60-130V
Experimental Deflection 3.5 micron stroke segment, 60 volts
Experimental Deflection - High Stroke 7.5 micron stroke segment, 130 volts