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)

Mir

ror

Sur

face

He

igh

t (n

m)

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

ctu

ato

r P

ositi

on (

nm)

-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 Data

Mean 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)

Pla

tfo

rm h

eig

ht

(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