1

MEMS Sensors and Bioimaging

Dr. Huikai Xie

Biophotonics & Microsystems Laboratory

Interdisciplinary Microsystems Group

Department of Electrical and Computer Engineering

University of Florida

January 5, 2005

Outline

Introduction: What’s MEMS?

MEMS Research at UF

Integrated Inertial Sensors

Micromirrors

MEMS-Based Optical Imaging

What Is MEMS?

Micro Electro Mechanical SystemsOr Microengineering or Microsystem Technology (MST) (Europe)Or Micromachining (Japan)

Making miniature sensors and actuatorsInvolving almost every discipline Leveraging the existing IC technology Enabling technology for many emerging markets

What Is MEMS? – Application Areas

BiosensorsBiomedical imagingLab-on-chip Micro-pumps, …

Chemical sensorsMicro fluidicsMass spectroscopy…

Inertial sensorsGas sensorsPressure, liquid level, …

MicromirrorsAll-optical switchesMicrophonesMicrospeakers…

Ink-jet nozzles,Displays,Data storage,…

2

What Is MEMS? -- Renowned Examples

Micromirror arrays for compact projectorsAccelerometers for automotive airbagsMicromirrors for optical switchingRF MEMS switchesMany others

Texas Instruments’Digital Micromirror Device

Analog Devices’Accelerometer

Lucent Technology’s2D micromirror for optical switch

Raytheon RF MEMS capacitive switch

Interdisciplinary Microsystems Group (IMG)

Five faculty membersMechanical and Aerospace Engineering

• Mark Sheplak• Lou Cattafesta• Hugh Fan

Electrical and Computer Engineering• Toshi Nishida• Huikai Xie

MEMS Research at UF

MEMS Research at UF – Research Areas

• Acoustic MEMS– Devices for fundamental acoustic measurements, arrays, proximity, etc.

• MEMS Shear-Stress Sensors– Thermal and floating-element (optical & piezoresistive) devices

• Flow Control– Development of sensors, actuators, & real-time flow control algorithms

• BioMEMS– Microfluidics, biosensors, lab-on-a-chip devices, etc.

• CMOS MEMS– Development of MEMS sensors with integrated CMOS circuits

• Meso-Scale Energy Reclamation and Control– Piezoelectric-based reclamation/control; energy harvesting

• Optical MEMS (MOEMS)– Micromirrors, microlenses, microgratings– MEMS-based Optical Imaging

Dr. Xie’s MEMS Group

• The mission of BML is to develop portable/disposable biophotonicmicrosystems and wearable microsensors with improved performance, functionality and affordability to allow more people and people with disabilities to obtain better medical care and have better quality of life.

• The research approach is monolithic integration of multiple sensors/actuators, single-crystal silicon microstructures and electronics for high performance, small size, low cost and low power.

• Current research activities:– CMOS-compatible microfabrication technology development– Integrated inertial sensors; Interface circuits design; High-Q resonators– Optical MEMS: micromirrors, microlenses– MEMS-based optical imaging

• Current Sponsors:– National Science Foundation– Semiconductor Research Corporation– Florida Photonics Center of Excellence

Biophotonics & Microsystems Laboratory (BML)

3

Research Projects

CMOS-MEMS Process

Integrated inertial sensors

Interface circuits design

High-Q resonators

Optical MEMS: micromirrors, microlenses

MEMS-based optical imaging

Biophotonics & Microsystems Laboratory (BML)

CMOS-MEMS Process

metal-1metal-2metal-3

(a) Backside etch

CMOS-region

Single-crystal Si (SCS) membrane

poly-Si

oxide

(b) Oxide etch

STS: 12-sec etching130-sccm SF6, 13-sccm O2, 23 mT, 600 W coil power, 12 W platen power;8-sec passivation85-sccm C4F8, 12 mT, 600 W coil power, 0 platen power.

PlasmaTherm-790: 22.5-sccm CHF3, 16-sccm O2, 100 W, 125 mT for 125 minutes and then 100 mT for 10 minutes.

CMOS-MEMS Process (cont’d)

(c) Deep Si etchCMOS layer

STS: same as Step (a).

Flat structure

(d) Si undercutSCS layer (20~100µm)

Thin-film structure

STS: 130-sccm SF6, 13-sccm O2, 23 mT, 600 W coil power, and 0 platen power.

(a)

(b)

Research Projects

CMOS-MEMS Process

Integrated Inertial Sensors

Interface circuits design

High-Q resonators

Optical MEMS: micromirrors, microlenses

MEMS-based optical imaging

Biophotonics & Microsystems Laboratory (BML)

4

Top view

anchor

Self-test actuator

sense combfingers

proof mass

self-test actuator

z-spring

Z-axis CMOS-MEMS Accelerometer

Size: 0.5mm x 0.6mmResonance: 3.9 kHzSensitivity: 2.6 mV/g(calculated 4.0 mv/g)Range: > 10 gLinearity: 0.5% (F.S.) Noise floor: 1 mg/Hz1/2

(Brownian 2.5 µg/Hz1/2)

y

x

z

H. Xie, et al., J. MEMS, 2002

CMOS-MEMS Gyroscope

Electrical isolation of bulk silicon

Drive in xCoriolis acceleration sense in z

y-axis rotation detection

X-drive spring

proof mass

z-spring

X-drive comb fingers

Z-sense fingers

y

xz

Ωy

Coriolis acceleration:

xyz Va ×Ω⋅= 2

H. Xie, G. Fedder, IEEE Sensors Journal, 2003

Top viewanchor

X- sense combfingers

X/Y-spring

Z-spring

Triaxial CMOS-MEMS Accelerometer

y

xz

Y- sense combfingersZ- sense comb

fingers

H. Qu, H. Xie, IEEE Sensors Conference, 2004

Low-Power Low-Noise Interface Circuits Architecture

Low Noise• Noise Matching• High chopping

frequency (2 MHz)

Low Power• 2-stage, open-loop• Stage-1 optimized for noise• Staeg-2 optimized for signal

swing and linearity

DC biasing

Vm+

Vm-

Stage-1

Sensor offsetcancellation

DC offset cancellation

modulationDemod.

CL

Vout+

Vout-

φ

Cbp

vos1

vos2

Aaux

Stage-2

×1

×1

D. Fang, H. Xie, IASTED International Conference on Circuits, Signals and Systems, 2004

5

Applications of MEMS Inertial Sensors

• Low cost – Automobiles, computer games, motion detection

• Small size -- Camcorders, nano-satellites, health monitoring

• Integrated Inertial Measurement Unit (IMU) system

Traditional applications of inertial sensors

MEMS inertial sensors

Emerging applications

Research Projects

CMOS-MEMS Process

Integrated inertial sensors

Interface circuits design

High-Q MEMS Resonator for Trapezoidal Waveform Generator for Adiabatic Circuits

Optical MEMSMicromirrors

Microlenses

MEMS-based optical imaging

Trapezoidal Waveform Generation

x

yStator

Rotor

2d

2dd

h yCd

ε=

y1

C

yy1

11

h yCd

ε=

y2

y2

C1

0

v

Not considering fringing effect

SEM Picture of The Resonator

Sensing combsActuation combs

Resonator beam

Isolation beam

M. He, M. Frank, H. Xie, SPIE International Symposium on Nano- and Micro- Smart Systems, 2004

6

Research Projects

CMOS-MEMS Process

Integrated inertial sensors

Interface circuits design

High-Q resonators

Optical MEMSMicromirrors

Microlenses

MEMS-based optical imaging

Electrostatic Micromirror

1mm x 1mm mirrorRadius of curvature: 50 mmCurled 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

H. Xie, G. Fedder, J. MEMS, 2003

1-D Thermal Micromirror

• 40 µm SCS layer provides very good mirror flatness• Continuous response curve• Measured radius of curvature of the mirror = 50 cm

bimorph actuator

mirrorx

y

Poly-Si heater

Applied current (mA)

Rot

atio

n A

ngle

(deg

ree)

A. Jain, S. Todd, H. Xie, 2003 OSA Annual Meeting

2-D Thermal Micromirror

40 µm SCS layer provides very good mirror flatnessMeasured radius of curvature of the mirror = 0.33m

mirrorbimorph actuators

1mmframe

A’

bimorph frame actuator

A

1mm2

mirror

bimorph mirror actuator

A

A’

Substrate

Second Axis

First Axis

I2I2

frameI1

I1

A. Jain, Y. Pan, G. Fedder, H. Xie, IEEE Journal of Selected Topics in Quantum Electronics, 2004

7

• Resonant frequencies:

Mirror Actuator = 445 Hz Frame Actuator = 259 Hz

2-D Mirror for Display

4 x 4 pixel raster scan of a laser beam by the mirror

A. Kopa, A. Jain, H. Xie, OSA Optics in Southeast, 2003

Large-Vertical-Displacement Device

Device size: 0.7mm by 0.4mm

Mirror size: 0.25mm by 0.25mm

Vertical Displacement: 200µm

Drive voltage: 15V

A. Jain, H. Xie, Sensors & Actuators, 2005

mirror

frame

mirror actuatorframe actuator

Substrate

θ

θ

ρ

l

Zmir

frame

Lf

- metal, - oxide- silicon, - polysilicon,

bimorph mirror actuator

frame actuator

mirror

Substrate

θ

θ

ρ

l

Zmir

frame

Lf

- metal,- metal, - oxide- oxide- silicon,- silicon, - polysilicon,- polysilicon,

bimorph mirror actuator

frame actuator

mirror

Tunable Microlens

Device size: 0.7mm by 0.4mm

Lens size: 0.15mm in diameter

Numerical Aperture: 0.35

Focal length: 0.2mm

Vertical Displacement: 200µm

Drive voltage: 15V

A. Jain, H. Xie, IEEE MEMS 2005

PR microlens

reflection of microlens

Research Projects

CMOS-MEMS Process

Integrated inertial sensors

Interface circuits design

High-Q resonators

Optical MEMSMicromirrors

Microlenses

MEMS-based optical imaging

8

Optical Bioimaging: Motivation

Heart disease and cancer are the top two killers in US

Lack of in vivo imaging modalities

Lack of high-resolution imaging for early cancer diagnostics

X-ray (safety, dye, resolution, …)

Ultrasound (~100µm)

Higher resolution (1~10µm ) in vivo imaging is needed

Optical Coherence Tomography

x1 x3x2V

x1 x3x2

n×

x

Broadband light source (λ, ∆λ)

BeamsplitterPhoto-

detector

Tissue

Reference mirrorAxial scan

Transverse scanTransverse scanTransverse scanTransverse scanTransverse scan

x

Optical Coherence Tomography first demonstrated by Fujimoto et al in 1991Non-invasive or minimal invasiveBased on low coherence interferometryHigh Resolution (∝ λ2/∆λ, <10µm) cross-sectional images

• Endoscopic imaging requires fiber probes that can transversely scan the tissue

OCT Imaging using Optical MEMS

Our solution: use a small moving mirror inside the probe (MEMS Mirror)Small size for internal organ imagingFast scanning speed for real-time imaging

Sample

Fiber-optic probe

5 mm

BBS

Signal Processing

PD

ReferenceMirror

Beam SplitterMEMS Mirror

GRINLens

Fiber

MichelsonInterferometer

Micromirror

FerruleLaser

Sample

mirror

MEMS-OCT Imaging Experiments

In vivo 2-D Endoscopic OCT of porcine bladder

U

MS

SMU:urothelium, SM:submucosa, MS: muscularis layer. Image size: 500×1000 pixels covering an area of 2.9×2mm2.

3.6×2.8mm2 4.3×2.8mm2

Y. Pan, H. Xie, G. Fedder, Optics Letters, 2001

T. Xie, H. Xie, G. Fedder, Y. Pan, Applied Optics, 2003

9

High mortality of cancers is due to lack of early detection modalities. Commonly used biopsy is risky and has low early detection rate. Optical coherence tomography (OCT) is a non-invasive high-resolution imaging technique, but conventional OCT is bulky and not suitable for in vivo internal organ imaging; and OCT has poor lateral resolution.

Motivation Objectives

Design Concept

MEMS-Based Endoscopic Optical Confocal Imaging

Develop miniature optical confocal microscopic (OCM) imaging probes using MEMS technology for noninvasive in vivodiagnosis of early cancers of internal organs.Promote interdisciplinary education, higher engineering and minority enrollment.

The basic idea is to use oppositely tilted bimorph beams to compensate the tilted platform, and thus the mirror or lens will move vertically when a current is applied to both bimorph actuators.

Schematic of the Proposed µ-OCM system: (OCT + MEMS Confocal Microscopy)

µOCM Probe

LVD µlens50:50Broadband

source

Photo detector

Reference µmirror

Fiber

SampleBeamsplitter µOCM

probe

µMirror

Anchor

Bimorph actuator II

Frame

AA’

Bimorph actuator I

FrameSilicon

Al

Oxide

Mirror

Sample

µ-OCM probe includes a MEMS mirror and a z-scan microlens

Bi-directional Micromirror Large Z-scan Microlens

Bimorph actuator IImicrolens

A A’

Bimorph actuator I

Anchor

Frame

Silicon

Frame

Poly-Si

±30°

~2 mm

Summary

Core Research AreasMEMSMicro/nano fabrication technologyIntegrated sensors, gyroscopes, accelerometers, IMUsOptical MEMS, micromirrors, microgratingsFiberoptic sensors

ApplicationsBiomedical imaging, optical coherence tomography (OCT)MEMS-based confocal imagingLaser scanning displaysBeam pointing and beam scanning systems for laser radar systemsNavigation control for space and automobilesInfrastructure vibration monitoringHealth monitoring

AcknowledgementsSponsors

National Science FoundationSemiconductor Research CorporationNASAFlorida Photonics Center of Excellence

Collaborators Dr. Yingtian Pan and Dr. Tuqiang Xie (SUNY-Stony Brook)Dr. Gary Fedder (Carnegie Mellon University)Dr. Jannick Rolland (CREOL, University of Central Florida)

StudentsDeyou Fang Maojiao HeAnkur JainAnthony Kopa Hongwei QuShane ToddBryan Blackburn