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EEL6935 Advanced MEMS 2005 H. Xie 1
Lecture 20Optical MEMS (2)
Agenda:
MOEMS Introduction
Micromirrors
3/30/2005
EEL6935 Advanced MEMS (Spring 2005) Instructor: Dr. Huikai Xie
EEL6935 Advanced MEMS 2005 H. Xie 2
Optical MEMS TopicsIntroduction to MOEMS
Optical bench on chip; Smart dust; Optical communicationsOptical MEMS Devices
Reflective– Micromirrors
Refractive– Microlenses– Microprisms
Diffractive– Microgratings– Microlenses (Fresnel)
WaveguidesInterference-based
– Filters– Tunable VCSELs– Microspectrometers
Uncooled Infrared DetectorsPhotonic crystals
MEMS-based Optical Imaging
EEL6935 Advanced MEMS 2005 H. Xie 3
Today’s Topic
Introduction to MOEMSOptical bench on chipSmart dustOptical communications
Electrostatic mirrorsParallel-plateVertical comb drivesLateral comb drive with a vertical lever
A self-contained, millimeter-scale sensing and communication platform for a massively distributed sensor network.
This device will be around the size of a grain of sand and will contain sensors, computational ability, bi-directional wireless communications, and a power supply, while being inexpensive enough to deploy by the hundreds.
H. Xie and G.K. Fedder, ASME International Mechanical Engineering Congress and Exposition, New York, NY, Nov. 11-16, 2001
Curled-Hinge Comb Drive: Concept
EEL6935 Advanced MEMS 2005 H. Xie 14
Vertical Comb Drive-1
Curled-Hinge Comb Drive: Mirror Design
EEL6935 Advanced MEMS 2005 H. Xie 15
Vertical Comb Drive-1
22cos1
22V
ddC
lNV
dzdCNFz ⋅⋅
⋅⋅=⋅⋅=
αα
( ) ( ) ( ) ( )2210
2 1211
21 zzzzzA ol ∆−++
−=
−=
αθαθα
tantan
( ) ( )gA
Cαε
α 0=
H. Xie et al, Journal of MEMS, 2002.
Curled-Hinge Comb Drive: Analytical Analysis
EEL6935 Advanced MEMS 2005 H. Xie 16
Vertical Comb Drive-1
Curled-Hinge Comb Drive: Analytical Analysis
• The rotation saturates after certain drive voltage
• But maximum angular rotation can be increased by using thicker comb fingers
• Placing the comb drives closer to the rotational axis can increase the maximum rotation angles.
EEL6935 Advanced MEMS 2005 H. Xie 17
1mm x 1mm mirrorRadius of curvature: 50 mm
Curled combs designed to obtain bi-directional rotationComb pairs placed to achieve differential torque and cancel z displacementZ-actuators included to adjust z-motion
1B
1A’
2B
1B’
1A
2B’
2A’2A
anchor anchor
Z-actuator
+ -V
F+ -V
F
Vertical Comb Drive-1
Curled-Hinge Comb Drive: Fabricated Mirror
EEL6935 Advanced MEMS 2005 H. Xie 18
Stator fingers
Rotor fingers
Metal-1 mesh
Curled Comb Drive Comb Finger Ends
5.0µm
40µm
z
θy
Static Response Frequency Response
Frequency (Hz)Voltage (V)
Dis
plac
emen
t (m
)
Tilt
Ang
le (d
egre
e)
Vertical Comb Drive-1
EEL6935 Advanced MEMS 2005 H. Xie 19
Staggered Comb Drive
R. Conant et al. (UC-Berkeley), Hilton Head 2000
Vertical Comb Drive-2
• Silicon wafer-to-wafer bonding
• Single-crystal silicon based micromirror
• Flat
• Large size: 550µm diameter
• Large angular deflection: Optical scan angle of 24.9ºat its 34 kHz resonant frequency
EEL6935 Advanced MEMS 2005 H. Xie 20
Angular Comb Drive Actuator
Patterson et al (UCLA), OFC 2002
Vertical Comb Drive-3
Photoresist reflow
EEL6935 Advanced MEMS 2005 H. Xie 21
Post-MUMPs DRIE process
Vertical Comb Drive-4
Piyawattammetha et al (UCLA), OFC 2003
• Mirror diameter: 1mm • Mirror radius of curvature: 40cm• +/-6° at 55 V d.c.
• Post-MUMPs process• Backside DRIE etch• Wet etch (BHF) for release• Single-crystal silicon structures• Manually assemble the tilt fingers using latches