Thin deformable mirrors for a reconfigurable space telescope
High-Performance MEMS-Based Deformable Mirrors for Adaptive Optics Iris AO, Inc.
description
Transcript of High-Performance MEMS-Based Deformable Mirrors for Adaptive Optics Iris AO, Inc.
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