cmos-mems

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CMOSCMOS--MEMS Inertial Sensors and TheirMEMS Inertial Sensors and Their

ApplicationsApplications

Hongwei Qu

Department of Electrical and Computer Engineering

Oakland University

Rochester, Michigan

Huikai XieDepartment of Electrical and Computer Engineering

University of FloridaGainesville, Florida

2007 CMOS Emerging Technology Workshop, Whistler, BC Canada, July 12, 2007

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Outline

Introduction

MEMS and CMOS-MEMS Technologies

Thin-Film CMOS-MEMS

DRIE CMOS-MEMS

Process Development and Improvement

Integrated CMOS-MEMS Inertial Sensors

MEMS Inertial Sensors: Applications

3-Axis Accelerometer

Design, Fabrication and Characterization

Integrated Gyroscope Introduction Design and Fabrication

Summary

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Introduction: MEMS Fabrication

General MEMS Services

MUMPs

MEMS Exchange

SUMMiT

MOSIS

Limitations

Most are for surface MEMS

Poly-Si based structures

Size limitation

Large parasitic

Wet release Other Technologies

SOI

Wafer/glass bonding

SUMMiT IV technology. Source: Sandia

SiO2 (0.63m)Si3N4 (0.8m)

MMPoly0 (0.3m)

SACOX2

(0.5m TEOS)

11m

Non-CMOS compatibility!

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Introduction: CMOS-MEMS

CMOS-MEMS Technologies

Full CMOS compatibility

Low cost through mainstream CMOS foundries, no assembling

High integration, high overall performance

Multi-functional devices

Technological Approaches

Pre-CMOS (Sandia)

Intra-CMOS (iMEMS, ADI)

Post-CMOS (No foundry limit)

Additional layers to CMOS

Post-CMOS refractory metal/Poly Si deposition (not traditional

CMOS process- no metallization )

Post-CMOS SiGe/Ge deposition

Post-CMOS etch (Wet or dry)

Pre-CMOS Source: Sandia

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Post-CMOS MEMS: Prototyping Flow

Post-CMOS Device Design and Fabrication Flow

Electrical

Design

Structural

and ProcessDesign

Device Design

FoundrySelection

CMOS FoundryProcess

Post-CMOS

Microfabrication

Tape-out

Wafer or die level

No harm to CMOS

Device Package

and

Characterization

Technological

Requirements

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Dry Post-CMOS MEMS

Particular Features

Multiple metal layers

Flexibility in wiring and low parasitics

Maskless dry process

Previous Approaches

Thin film post-CMOS technology

Easy process

Curled structure

Temperature dependence

Size limit (400 m420 m)

Release holes needed small proof

mass

DRIE post-CMOS technology

Bulk MEMS performance with thin-film

MEMS footprint

Wu et al, IEEE Solid-state Circuits, 2004

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Backside etch.

DRIE CMOS MEMS Technology

Metal 4 removal by wet etch.Chips from TSMC foundry.

DRIE Post-CMOS MEMS: Process Flow

Performing thin film undercut andSCS structure etch independently

1st SiO2 etch

Si DRIE undercut of isolation beams

Si DRIE for device release

No undesired undercut

2nd SiO2 etch

Metal 4 is usedCMOS region

Thin film

region

Other MEMS

structures

Qu et al, IEEE Sensors, 2004

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Technical Issues

Timing controlled etch

Overheating of suspended

structures

Contamination

Isolation trench

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Backside etch.


Metal 4 removal by wet etch.Chips from TSMC foundry.

1st SiO2 etch

Si DRIE undercut of isolation beams

Improved DRIE CMOS-MEMS

PR coating

Other material

Footing effect

PR ashing for device release

H. Qu, et al, Solid State Sensors Workshop, Hilton Head Island, 2006

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Transition

Introduction CMOS-MEMS Technology Thin-Film CMOS-MEMS

DRIE CMOS-MEMS Process Improvement

Integrated CMOS-MEMS Inertial Sensors MEMS Inertial Sensors: Applications

3-Axis Accelerometer Design, Fabrication and Characterization

Integrated Gyroscope Introduction

Design and Fabrication

Summary

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MEMS Inertial Sensors

Applications: Everywhere in modern life Vehicle safety

Seismetic and Engineering monitoring

Health/Athletic monitoring Virtual reality, image stabilization

Logistic, transportation

Consume electronics (PC, Playstation)

Portable electronics (MP3, cell phone, etc.)

Requirements Smaller size for 3-axis sensing

Low power Low-noise (high resolution)

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Device Design

Simplified 3D model of the device

3-axis DRIE Accelerometer

XY

Z

Imbalanced Z

proof mass

Lateral proof mass

X, Y fingersZ torsional beams

X, Ysprings

Z fingers

Si

substrate

Circu

itsCK

T

H. Qu, et al, Solid State Sensors Workshop, Hilton Head Island, 2006

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Device Design

Lateral sensing

Fingerlength

C1 C2

gap

Stator

Rotor

Sensing Mechanisms

1C dx

Cgap

ma F k dx

= =

Z-axis sensing

C1

Vm+

Vm-

Stator Stator

Cb

Ca

Rotor

M1

Fully differential sensing in all three axes?

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Fully Differential Configuration

Lateral Sensing

Vm-Vm+

Vout+ Vout-

C1a

C3a

C1b

C3bC2b

C4b

C2a

C4a

driving combfingers

sensing combfingers

Vm+

Vm-

C1a

C3a

C3b C1b

C4b C2b

C2a C4a

Vm+

Vm-

C1

C2

C3

C4

Vout+ Vout-

4 groups of sensing comb fingers with common-centroid wiring for CM rejection

mechanical

spring

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Two groups on each end for offset cancellation swapped connections for a common-centroid

configuration

C1 = C1b+C2a = C2= C1a+C2b

C3 = C3b+C4a = C4= C3a+C4b(at original displacement)

z

xy

C1b

C1a

C2b

C2a

Vm+

Vm-

Vs

Torsional beams and anchors

Z-Axis Sensing

Offset cancellation

Fully differentialsensing

C2a, C2b

C1a, C1b

Stators

C3a, C3bC4a, C4b

L L Vm+

Vm-

Vs1

C2a

C1a

C1b

C2b

C1

C2

Vm+

Vm-

Vs1C2

C1

M1

M3

M2Vm+

Vm-

Vs

C1 C3

C2 C4

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Device Design: Interface Circuit

Low-power, low-noise dual-chopper amplifier

D. Fang et al, VLSI Symposium 2006

Low-power: 1mW

AA battery: 1000 hours

Low noise: 16 nV/Hz

Total gain: 44dB

Dual chopper: 1 MHz and

20 kHz Offset cancellation

2 2 2 2( )e

n m e m

Va a a a

S= + = +

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3-axis DRIE Accelerometer Design: Summary

440 fF in lateral

86 fF in Z

Total capacitance

1.6~2.5 mV/gSensitivity in Y

4.5 mV/gSensitivity in Z

1 mW / axisPower dissipation

1~ 10 g/HzBrownian Noise floor

1.5~2.3 mV/gSensitivity in X

2.1mFinger gap

40 mLength of z finger

90 m (overlap 85 m)Length of x_y fingers

50 m Silicon+6 mCMOS

Thickness of thestructure

1000*1000m2Device size

3-axis

Cadence layout of the devices

CKT for 1-axis acclCKT for YX-CKT

Z-CKT Test CKT

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3-axis Accelerometer: Fabricated Devices

3 mm

3mm

y-axiscircuit

x

-axis

c

ircuit

z-axis

circuit

Packaged Devices

PLCC-52 package Photo of a bonded die.

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90

m

(a

)

1mm

1mm

300m

700 m

3-axis Accelerometer: Microstructures

Isolationtrenches

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3-axis Accelerometer: Characterization

Test Setups Rotary table

Hand-heldshaker

Spectrumanalyzer

shaker

Referenceaccelerometer

Kistler8638B5

DUT

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3-axis Accelerometer: Characterization

Static test results of the 3-axis

accelerometer

Static Response and Noise Test0.05g Pk

12 g/Hz

0.5g Pk

110g/Hz

0.5g Pk

110g/Hz

Noise spectrum of the lateral andz-axis accelerometer

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Summary of the 3-Axis Accelerometer

0.30.35 (L)2.11/4.71 (z)

-No-linearity (%)

350110.0-Z-axis noise floor (g/Hz)

1.6 (lateral)/0.6 (z)1.51.5 (lateral) /0.5 (z)Bandwidth (kHz)

12.26~2.38(L)

2.11~4.71 (z)

Inter-axis coupling (%)

17.03-TCO (mg/C)

0.01-0.307TCS (%/C)

87.9(L)/73.4(z)Dynamic range (dB) (BW=100Hz)

28012.07.97Lateral-axis noise floor (g/Hz)

270~330320240Z-axis overall sensitivity (mV/g)

270~330460450Lateral-axis sensitivity (mV/g)

-2.022.4Z-axis mechanical sensitivity

-3.544.5Lateral-axis mechanical sensitivity (mV/g)

0.6 ~ 1.1511Power consumption (mW)

44 (with package)-33Chip size (mmmm)

ADXL330TestedDesignedParameter (Unit)

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Rotational Sensing Principle: Coriolis Acceleration

Device Design and Fabrication

Lateral driving, lateral sensing

DRIE CMOS-MEMS

Integrated CMOS-MEMS Gyroscope

2c

a v = rr r

Fabricated Integrated gyroscope

Driving comb

fingers

Driving

mechanical

spring

Sensing

spring

Sensing

comb fingersProof mass

X

Y

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Summary

CMOS-MEMS

Monolithic Integration

High performance, low Cost

CMOS-MEMS Inertial Sensors

Bulk silicon microstructures with footprint of surface

devices

High resolution

Emerging Applications

Portable electronics Security

Wireless sensor networks

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Acknowledgements

NASA UF/UCF Space Research Initiative

MOSIS Educational Program

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Z-Axis Sensing: Mechanisms

Coventor simulation of Z capacitance change and displacement versus Z acceleration(using 3 swapped fingers)

-200 -150 -100 -50 0 50 100 150 2006

7

8

9

10

11

12

13

Acceleration in z direction (g)

Capacitance(fF)

-200 -150 -100 -50 0 50 100 150 200-10

-5

0

5

10

Maximumd

isplacementinzdirection

(um)

-200 -150 -100 -50 0 50 100 150 200-2

-1

0

1

2


Maximumr

otaionalangle(degree)

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Z-Axis Sensing: Mechanisms

Coventor simulation of Z capacitance change.

-50 0 50-1

0

1

2

3

4

5

6

7

8

9


Capacitance(fF)

y = 0.0024*x - 2.1e-018

C1

C2

C1b

C1a

1 2

1 2

C C

C C

+

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DR by S/N

Dynamic Range by S/NRatio

Y-axis of R5

THD=5%

DR=103.6-20.90=82.7 dB

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