High-Performance MEMS-Based Deformable Mirrors for Adaptive

Optics

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 Inc

Iris AO Segmented MEMS DM

• Robust assembled mirror surface stays flat

• Temperature insensitive bimorphs elevate mirror above substrate

• Piston/tip/tilt electrostatic actuation

Ele c tro d e s

Bim o rp hFle xure

Bo nd site

M irro rSe gm ent

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

Scalable Assembly: 367 Demo

DM Stroke: Position vs. Voltage

• Nonlinear position• Very repeatable

2nd Generation Assembled Mirrors

2nd Generation Assembled Mirrors

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

Surface Figure vs. Temperature

-400 -300 -200 -100 0 100 200 300 4000

10

20

30

40

50

60

70

80

90

100Mirror Surface Figure ( T=-150C)

Position (m)

Mirr

or S

urfa

ce H

eigh

t (nm

)

Thin-Film DMCurrent Iris AO DMProposed Iris AO DM

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

Bimorph-Flexure Temperature Stability

-50 -25 0 25 50-200

-150

-100

-50

0

50

100

150

200Mirror-Position Temperature Sensitivity

Temperature (C)

A

ctua

tor P

ositi

on (n

m)

-42nm/ C

-2nm/ C

0.1nm/ C

Original Nickel Bimorph Flexure2nd Generation Bimorph FlexureProposed Low-Drift Multimorph

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

Detailed Position vs. Voltage DataMean platform height vs. applied V, FSC37-01-02-0507 Segment 1

14

15

16

17

18

19

20

0 10 20 30 40 50 60 70

Applied voltage (V)

Plat

form

hei

ght (

um)

Platform height, A,B,C (V increasing) Platform height, A,B,C (V decreasing)

Platform Height, A only (V increasing) Platform Height, A only (V decreasing)

Platform Height, A, B only Platform Height, C only

Platform Height, B, C only Platform Height, A, C only

Platform Height, B only

Experimental Deflection

3.5 micron stroke segment, 60 volts

Experimental Deflection - High Stroke

7.5 micron stroke segment, 130 volts

Experimental Deflection - 7 segments