lecture 20 optical mems (2) · lecture 20 optical mems (2) ... curled combs designed to obtain...

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


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


Today’s Topic

Introduction to MOEMSOptical bench on chipSmart dustOptical communications

Electrostatic mirrorsParallel-plateVertical comb drivesLateral comb drive with a vertical lever

Fabrication Processes– Thin-film– Bulk silicon

AssemblyIntegrated


Developed by Prof. M. Wu’s group at UCLA

Optical Bench On Chip


http://misob.lg-elite.com/tech_repo/SiOB.pdf

LG Electronics Institute of Technology

Optical Bench On Chip


Hybrid Integration

http://photonics.dupont.com/downloads/HybridIntegrationPlatform.pdf

Tunable Optical Transmitter


Smart Dust

1.2mm

mirror

Sensor Detector/Receiver

Solar Cell

• K. Pister’s group (UC-Berkeley)


Smart Dust

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.

Potential Applications:Weather/seismological monitoring on MarsInternal spacecraft monitoringLand/space comm. networksChemical/biological sensorsWeapons stockpile monitoringDefense-related sensor networksProduct quality monitoring……

P. B. Chu et al., MEMS 1997


Inventory Location AwarenessFactory and Process AutomationSeismic and Structural MonitoringTraining and Systems Integration

Wireless Sensor Network

Indoor/Outdoor Environmental MonitoringSecurity and Tracking Health and Wellness MonitoringPower Monitoring

Cell Phoneor Wi-Fi

Storage Base Station

Environmental SensorsRadio Mesh Networks

Wireless Sensor Node(Sensor + Mote)

Crossbow Technology, Inc.www.xbow.com


Micromirrors: Electrostatic

Electrostatic MicromirrorsParallel-plateVertical comb driveLateral comb drive with vertical conversion

Fabrication Processes– Thin-film– Bulk silicon

AssemblyIntegrated


Easy ImplementationTradeoffs:

Rotation angle; size; drive voltage

Texas Instruments’ Digital Micromirror Devices (DMD)

Parallel-Plate Electrostatic Micromirrors

Lucent Technologies’ 2D Micromirror


Electrostatic Micromirrors

Vertical comb drivesComb fingers with multiple conductor layers

– Carnegie Mellon Univ.Curled-hinge comb drives

– Carnegie Mellon Univ.– Univ. of Florida

SOI-based staggered comb drives– UC-Berkeley– Stanford Univ.– UC-Davis

Photoresist reflow– UCLA

Others


Vertical Comb Drive-1

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



Curled-Hinge Comb Drive: Mirror Design



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



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.


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


Curled-Hinge Comb Drive: Fabricated Mirror


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)



Staggered Comb Drive

R. Conant et al. (UC-Berkeley), Hilton Head 2000


• 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


Angular Comb Drive Actuator

Patterson et al (UCLA), OFC 2002


Photoresist reflow


Post-MUMPs DRIE process


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


Buckled Comb Drive

• Vertically buckled bridge• Wet etch SiO2• Poly-Si as HF etching mask

Sasaki et al (Tohoku U.), JMEMS, vol.13 (2004)



Electrostatic Micromirrors

Lateral Comb DrivesHinges

– Sandia– UC-Berkeley – UCLA– …

Vertical levers– UC-Berkeley– …


• Gear Speed Reduction Unit• Micromirror and Drive Mechanism

Lateral Comb Drive -1

Hinged Thin-film Micromirror(Sandia National Lab.)


SOI Micromirror

Lateral Comb Drive -2

•SOI wafer•DRIE Si etch•LPCVD Si3N4 for anchors

•LPCVD poly-Si•Oxidize poly-Si•CMP

•LPCVD poly-Si•Si DRIE

•RTA 750~900°C•to form tensile stress•HF release•Supercritical drying

J.T. Nee et al (UC-Berkeley, MEMS 2000

Light-weight SOI MEMS Mirror


Torsional Mirror

Multilevel Beam Microstructures

V. Milanovic et al, JMEMS, vol.13 (2004)

Vertical Comb-Drive Mirror

Concept

Lateral Comb Drive-3

Lixia Zhou et al


• Torsional Micromirror

Multilevel Beam Fabrication

• Flat• Lightweight• High speed• Low power• Electrostatic actuation V. Milanovic et al, JMEMS, vol.13 (2004)

Lateral Comb Drive-3


Brief introduction of MOEMSDiscussed different types of electrostatic micromirrors

Parallel-plate– Small sizes/small angles

Vertical comb drives– Large angle; large size; good flatness– But more complicated fabrication

Lateral comb drives– Large angle; large size; good flatness– Complicated fabrication

Summary

lecture 20 optical mems (2) · lecture 20 optical mems (2) ... curled combs designed to obtain...

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