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Outline

1 Introduction

2 Basic IC fabrication processes

3 Fabrication techniques for MEMS

4 Applications

5 Mechanics issues on MEMS

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3. Fabrication Techniques for MEMS

3.2 Surface micromachining

3.3 LIGA process

3.1 Bulk micromachining

3.4 Hybrid micromachining

3.5 Thick micromachined structures

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3.4 Hybrid micromachining

• Hybrid micromachining – the fabrication processes containing both surface and bulk micromachining technique

• Presently, more and more MEMS devices are fabricated through hybrid micromachining technique

Q. Zou, Z. Li, and L. Liu, J. of MEMS, 1996

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C.-J. Kim, A.P. Pisano, and R.S. Muller, J. of MEMS, 1992

Micro Gripper

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+ Fabrication processes

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Resonant pressure transducer

surface micromachinedresonator

Surface micromachinedresonator

Bulk silicon etching

C.J. Welham, J.W. Gardner, and J. Greenwood, Transducer '95, 1995.

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Capacitive type pressure transducer

J.T. Kung and H.-S. Lee, J. of MEMS, 1992.

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Microphone

Q. Zou, Z. Li, and L. Liu, J. of MEMS, 1996

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DRIE trench

define wet anisotropic etch mask

define sacrificial layer

define structure layer

Wet anisotropic under etching

Electorstatic lever actuator

H.-Y. Lin and W. Fang, ASME IMECE 2000.

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Torque generatorFolded frame

define the structure layer

Remove the sacrificial layer

Wet anisotropic under etching

RIE trench

define wet under etching mask

define the sacrificial layer

Micro scanner

H.-Y. Lin and W. Fang, Transducer01, 2001

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Surface device Bulk device

Micro scanner

Surface+ Bulk device

J. Hsieh and W. Fang, Transducer99, 1999

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Define cavity and lower electrode

Pattern sacrificial layer

Pattern structural layer

Releasing structure and etching Si

Pattern top electrode (option)and then remove sacrificial layer

extending cavity

Deposit protection/isolation layer

+ Fabrication processes

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DRIE (~10 μm)

DRIE trimming SixNy passivation

Bulk etching (~100 μm)

MUMPsprocess (~1 μm)

MOSBE Fabrication Platform

M. Wu, C. Lai, and W. Fang, IEEE MEMS’04, the Netherlands, 2004M. Wu, C. Lai, and W. Fang, JMM, 2005

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• Increasing the stiffness of the thin poly-Si structures w/o changing the film thickness

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A B

A

B

AB

y (d

efle

ctio

n)

x (beam length)

y (d

efle

ctio

n)

Def

lect

ion

(μm

)

A

B

Position along the beam length (μm)0 140

0

0

9

9

U-shape cantilever

Conventional cantilever

Passive component - Stiff beam

H.-Y. Lin and W. Fang, JMM., 2000

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H.-Y. Lin and W. Fang, the ASME IMECE, Orlando, FL, 2000

Reinforced folded frame

Passive component - Flat mirror

H.-Y. Lin and W. Fang, Sensors and Actuators A, 2004

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ρ : 93mm ρ : 41mm ρ : 153mm ρ : 179mm

X axis-Profile435μm

Y axis-Profile435μm

X axis-Profile435μm

Y axis-Profile435μm

MOSBE mirrorConventional mirror

H.-Y. Lin and W. Fang, the ASME IMECE, Orlando, FL, 2000

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• Narrow trench-refilled poly-Si (depth ~ 20 μm)+ Double-ring reinforced rib on its boundary + Grid reinforced rib on its domain

M. Wu, C. Lai, and W. Fang, IEEE MEMS’04, the Netherlands, 2004

Passive component – Flat mirror

M. Wu, and W. Fang, JMM, 2005

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• Four different type mirror

Rib-reinforced structure

+ Thin film mirror (ROC: 19 mm) + Single ring mirror (ROC: 64 mm)

+ Double ring mirror (ROC: 92 mm) + Double ring with grid (ROC: 150 mm)

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Active component - Electrostatic actuator I

J. Hsieh and W. Fang, Transducers’99, Sendai Japan, 1999J. Hsieh and W. Fang, Sensors and Actuators A, 2000

Plate Torsional springDriving electrode

• META Engine : ((MMicroicro EElectrostatic lectrostatic TTorsionalorsional AActuator )ctuator )

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• EDLA Engine : ((EElectrostaticallylectrostatically--DDrivenriven--LLeverage everage AActuator )ctuator )

Outputdisplacement

Electrode

Pivot

Lever

Max disp. > 15μm Driving voltage < 25 volt

H.-Y. Lin, H. Hu, and W. Fang, Transducers’01, Munich Germany, 2001

Active component - Electrostatic actuator II

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• Vertical comb electrodes+ Comb thickness ~20um + Travel stoke ~20um

20um

Active component - Vertical comb actuator

M. Wu, and W. Fang, JMM, 2005

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Active component - electrothermal actuator

W.-C. Chen, J. Hsieh, and W. Fang, IEEE MEMS’02, Las Vegas, NV, 2002W.-C. Chen, J. Hsieh, and W. Fang, Sensors and Actuators A, 2003

Move upward

Move downward

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1000 10000 100000

-40

-35

-30

-25

-20

-15

-10

-5

Res

pons

e (d

B)

Frequency (Hz)

1.8 kHz 33 kHz

105 106 107 108 10930

31

32

33

34

35

reso

nant

freq

uenc

y (k

Hz)

number of cyclesNumber of cycles (million cycles)

0.1 1.0 10 100 1000

Frequency (kHz)

1.0 10 100R

eson

ant f

requ

ency

Res

pons

e (d

b)

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Vertical comb actuatorRib-reinforced mirror and frame

Torsionalspring

Applications – 1 axis optical scanner

M. Wu, and W. Fang, IEEE MEMS, Masstricht, the Netherlands, 2004M. Wu, and W. Fang, JMM, 2005

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Scanning test

M. Wu, and W. Fang, IEEE MEMS, Masstricht, the Netherlands, 2004

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00.20.40.60.81

0 1 2 3 4 5 6

Frequency(kHz)

Am

plitu

de

Resonant frequency ~1.8 kHz

Dynamic measurement

• Dynamic test driven by AC

0

1

2

3

0 10 20 30 40 50

Voltage (V)A

ngle

(deg

ree)

• Static load-deflection test + out-of plane displacement

~12.03μm at 50V+ scanning angle ~ 2.8 degree

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M. Wu, C. Lai, and W. Fang, IEEE MEMS’04, the Netherlands, 2004

Mirror (passive)

Driving electrodes (active)

Springs (passive)

Supporting frame (passive)

Applications - 2D Gimbal mirror

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Scanning test

Outer axis: 7.1kHz

Inner axis: 4.1kHz

• Scanning images

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• Scanning images

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Dynamic measurement

• Dynamic test driven by AC • Static load-deflection test

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H.-Y. Lin and W. Fang, IEEE Optical MEMS, Kauai, Hawaii, 2000H.-Y. Lin and W. Fang, the ASME IMECE, Orlando, FL, 2000

1 cm

Applications: optical scanner

EDLA engine

Mirror

Torsional spring

H.-Y. Lin and W. Fang, Sensors and Actuators A, 2004

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Excitation frequency (kHz)

Op

tica

l sc

an

nin

g a

ng

le(d

eg

)

0

1

23

4

5

6

7

8

9

10

0 2 4 6 8 10 12 14 16 18 20 22 24 26

Sine wave, ±18.5 VDC bias, 18.5 V1st torsional mode

4.2 kHz, 9.2 deg

2nd torsional mode17.7 kHz, 1.53 deg

• Measured frequency response