[PDF] - ME 645: MEMS: ME 645: MEMS: Design Fabrication Design Fabrication PDF Document

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ME 645: MEMS: ME 645: MEMS: Design Fabrication Design Fabrication

Lecture 15 and 16: MicroStereoLithography (MSL)

Design, Fabrication Design, Fabrication and Characterization and Characterization

P.S. Gandhi P.S. Gandhi Mechanical Engineering Mechanical Engineering IIT Bombay IIT Bombay

PRASANNA S GANDHI gandhi@me.iitb.ac.in PRASANNA S GANDHI gandhi@me.iitb.ac.in

Acknowledgments: Suhas Deshmukh (PhD 08) Rahul Ramtekkar (M Tech 08) and other M Tech students

Need for Microstereolithography Need for Microstereolithography

Motivation Motivation

Need for Microstereolithography Need for Microstereolithography

MEMS MEMS – – Worldwide Research attention Worldwide Research attention

Requirement of current actuating and sensing

Requirement of current actuating and sensing mechanisms to be of complex 3D shapes. mechanisms to be of complex 3D shapes.

Incorporation of a wide range of materials

Limitations of Conventional Limitations of Conventional processes : processes :

manufacture high aspect ratio and complex

manufacture high aspect ratio and complex 3D microstructures. 3D microstructures.

PRASANNA S GANDHI gandhi@me.iitb.ac.in PRASANNA S GANDHI gandhi@me.iitb.ac.in

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What is What is Microstereolithography Microstereolithography? ?

Novel

Novel microfabrication microfabrication

Laser beam

Part to manufacture

process for fabricating high process for fabricating high aspect ratio and complex 3D aspect ratio and complex 3D microstructures. microstructures.

Evolved from the rapid

Evolved from the rapid prototyping industry. prototyping industry.

UV laser beam scanned on a

UV laser beam scanned on a photopolymerizable photopolymerizable resin. resin.

3rd Layer 2nd Layer 1st Layer

UV Light

El Mirror

Curing of the resin layer by

Curing of the resin layer by layer. layer.

Stacking of all the layers.

In case of ceramic materials

In case of ceramic materials process of laser sintering is process of laser sintering is used used

Light

Elevator Vat of UV curable solution

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SLA to MSL SLA to MSL

Item Parameters Stereolithography Micro- stereolithography Optical System Spot Size Intensity profile

Approx. 100μm

Non-uniform during scanning Few μms Uniformity is necessary for high resolution Scanning System Resolution Less than 100μms is sufficient Less than 1μm is needed Photopolymer Viscosity High Low Support Generation Needed Is not needed

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Microstereolithography Microstereolithography

Process Types

Dynamic mask method (Integral MSL):

Dynamic mask method (Integral MSL):

– Expose the layer to be built at a time Expose the layer to be built at a time – Change the mask dynamically Change the mask dynamically – Expose the next layer Expose the next layer

Scanning method: Scanning method:

Scanning method:

Scanning method:

– Scan one layer by focused laser beam and Scan one layer by focused laser beam and then the next layer then the next layer

PRASANNA S GANDHI gandhi@me.iitb.ac.in PRASANNA S GANDHI gandhi@me.iitb.ac.in

Microstereolithography Microstereolithography

Dynamic mask process Integral MSL systems

Dynamically changing Dynamically changing

Dynamic Mask Elevetor z

Dynamically changing Dynamically changing mask according to the mask according to the section to be exposed section to be exposed

Computer Laser curable photopolymer

Generates image of a layer and complete layer is build in single layer

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Scanning Method Scanning Method

Classical

Classical msl msl

– Focusing by a dynamic lens Focusing by a dynamic lens – Use of galvanometric mirrors Use of galvanometric mirrors

Theoretical best point of

Theoretical best point of focus not intersecting the focus not intersecting the resin surface. resin surface.

Free surface technique Free surface technique

Micro computer C.A.D. Z - stag Galvanometric X-Y mirrors U.V. Laser Dynamic Acousto optical shutter

Free surface technique

All optical parts fixed

X-

Y

Y-

Z motorized translation

Z motorized translation stage stage Thickness and uniformity Thickness and uniformity control of deposited liquid layer control of deposited liquid layer difficult difficult

ge Photoreactor y focusing lens

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Scanning Method Scanning Method

Schematic diagram

Schematic diagram

Laser Mirror Elevator z

Vector Scan

Laser curable photopolymer

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Various MSL Systems Various MSL Systems

Scanning method or vector by vector MSL.

Scanning method or vector by vector MSL.

Various ways of scanning Various ways of scanning Various ways of scanning Various ways of scanning

Integral

Integral microstereolithography microstereolithography.

1. Liquid crystal display as pattern generator
1. Liquid crystal display as pattern generator
2. Digital
2. Digital micromirror

micromirror device as pattern device as pattern generator generator

Creating an object inside reactive

Creating an object inside reactive medium medium

1 Two photon process 1 Two photon process 1.Two photon process 1.Two photon process

2. Single
2. Single photon

photon process process

Method of layer preparation

Method of layer preparation

1. Constrained surface technique.
1. Constrained surface technique.
2. Free surface technique
2. Free surface technique
3. Super IH (Integrated Harden) process technique
3. Super IH (Integrated Harden) process technique

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Constrained and Free Constrained and Free Surface MSL Surface MSL

UV Source Optical Shutter Constrained Surface UV Source Optical Shutter Free Surface

C t i d S f MSL S t C t i d S f MSL S t

XY Stage Micro- Controller Surface Z-Stage Fabricated Structure Resin Tank

F S f MSL S t F S f MSL S t

XY Stage Micro- Controller Surface Z-Stage Fabricated Structure Resin Tank

Constrained Surface MSL Systems Constrained Surface MSL Systems Features: Features:-

Transparent Glass Window is used

Transparent Glass Window is used Controls layer thickness Controls layer thickness

Laser spot is at focus on the resin

Laser spot is at focus on the resin

XY Scanning by Resin Tank Motion

XY Scanning by Resin Tank Motion

Destruction of fabricated part

Destruction of fabricated part Free Surface MSL Systems Free Surface MSL Systems Features: Features:-

Layer thickness is controlled by

Layer thickness is controlled by Recoating blade Recoating blade

XY Scanning by Resin Tank Motion

XY Scanning by Resin Tank Motion

No Destruction of fabricated part

No Destruction of fabricated part

Waviness of fabricated part due to tank

Waviness of fabricated part due to tank motion motion

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Scanning Method Scanning Method

Variations

1. Fixed optics, move liquid tank for xy
1. Fixed optics, move liquid tank for xy

scanning scanning

2. Various ways for scanning
2. Various ways for scanning
Rotating galvano

Rotating galvano-

scanning mirrors

scanning mirrors Linea l mo ing mi o s (no el a ) Linea l mo ing mi o s (no el a )

Linearly moving mirrors (novel way)

Linearly moving mirrors (novel way)

Raster scan vs vector scan

Raster scan vs vector scan

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Various Scanning Various Scanning Methods Depicted Methods Depicted

L M L M Post-objective Pre-objective Photo-reactor tank Off-axis Lens M L M L M M L

Proposed by us recently * p y y

Suhas Deshmukh, S. Dubey, P.S. Gandhi, “Optical Analysis of Scanning Microstereolithography systems”,

Proceedings of the SPIE Symposium on MOEMS-MEMS Micro & Nanofabrication, San Jose, CA USA, January 2006

Suhas P. Deshmukh, P.S. Gandhi, “Optomechanical Scanning Systems for Microstereolithography (MSL):

Analysis an Experimental Verification”, Journal of Material Processing Technology

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Issues

Scanning Method Scanning Method

Factors affecting resolution of components:

Factors affecting resolution of components:

– Laser intensity Laser intensity – Motion and quality of the beam Motion and quality of the beam – Photopolymer/ monomer used Photopolymer/ monomer used Focusing Focusing – Focusing Focusing – Exposure Exposure

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System Details System Details

Typical System Components Typical System Components Typical System Components Typical System Components

Laser

Beam delivery system

Computer controlled precision stages and a

Computer controlled precision stages and a CAD design tool CAD design tool

Process monitoring system with a CCD

Process monitoring system with a CCD camera. camera.

UV curable resin

UV curable resin – – HDDA (1,6 HDDA (1,6 – – Hexanediol Hexanediol diacrylate) diacrylate)

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Components of Components of system system

Software CAD Model Slicing Algorithm

PC Ar+ Ion Laser XY Scanning Micro-controller AOM

Scan Path Generation Photopolymerization

Schematic of Scanning MSL system

Z-Stage Photopolymer Vat

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Laser Laser

UV Lamps

He

He-

Cd Laser

Cd Laser

Argon Ion Laser

Argon Ion Laser Typical specifications : Typical specifications :

Name of the supplier : Coherent Inc. Name of the supplier : Coherent Inc. Product model : Innova 300 Series (I Product model : Innova 300 Series (I-304) (Ar 304) (Ar+

+ Laser)

Laser) Product model : Innova 300 Series (I Product model : Innova 300 Series (I 304) (Ar 304) (Ar Laser) Laser) Multiline UV wavelengths : 333.4nm to 363.8nm Multiline UV wavelengths : 333.4nm to 363.8nm Power : 200mW Power : 200mW Diameter (@ 1/e Diameter (@ 1/e2 points) in mm : 1.5mm points) in mm : 1.5mm Divergence (full angle) in mrad : 0.5 Divergence (full angle) in mrad : 0.5

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Fundamentals of Laser Beam Fundamentals of Laser Beam Propagation Propagation

w0

Gaussian Beams Gaussian Beams

waist (z = 0)

w(z ) R(z )

Gaussian Beams Gaussian Beams

Beam waist at z = 0, where the spot size is w Beam waist at z = 0, where the spot size is w0. Expansion to w = w(z) with distance z away Expansion to w = w(z) with distance z away from the laser. from the laser. The beam radius of curvature, The beam radius of curvature, R(z), also , also increases with distance far away increases with distance far away. .

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Fundamentals of Laser Beam Fundamentals of Laser Beam Propagation Propagation

Expressions for spot size, radius of curvature,

where where zR is the Rayleigh Range (the distance is the Rayleigh Range (the distance

ver which the beam remains about the same
ver which the beam remains about the same

p p , ,

( )

2 2

( ) 1 / ( )

R R

w z w z z R z z z z = + = +

ver which the beam remains about the same
ver which the beam remains about the same

diameter), and it's given by: diameter), and it's given by:

2 R

z w π λ ≡

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SLIDE 10

10 Fundamentals of Laser Fundamentals of Laser Beam Beam Focussing Focussing

G i G i

d

Gaussian Gaussian Beam Beam Focusing Focusing

D z ≈ f d0

Airy Disk formula for spot size:

z f w0 w (f)

2.44 ( / ) d F D λ =

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UV UV-

curable Resin

curable Resin

Desired Properties: Desired Properties:- Desired Properties: Desired Properties:

Photosensitivity at the operating wavelength

Low viscosity to produce a smooth surface

High curing speed

Low shrinkage during polymerization

High absorption for low penetration of light

High absorption for low penetration of light.

Types of Resins Types of Resins

1) 1)Epoxy Resins

Epoxy Resins

2) 2)Acrylate resins

Acrylate resins

HDDA (1,6 HDDA (1,6 – – Hexanediol diacrylate) with 4% by wt. photoinitiator Hexanediol diacrylate) with 4% by wt. photoinitiator

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Mathematical Mathematical Modeling Modeling

Laser exposure along the X

Laser exposure along the X Axis defined as Axis defined as

Laser exposure along the X

Laser exposure along the X-Axis defined as Axis defined as

Curing depth working equation : Lw

2 2

2

2 ( , )

p

z y D w s

P E y z e e W V π

− −

⎛ ⎞ = ⎜ ⎟ ⎝ ⎠ E ⎛ ⎞

Cured Line width: y z x zmax = Cd max

ln

d p c

E C D E ⎛ ⎞ = ⎜ ⎟ ⎝ ⎠

0.5 max

2 ln

w c

E L W E ⎛ ⎞ ⎛ ⎞ = ⎜ ⎟ ⎜ ⎟ ⎜ ⎟ ⎝ ⎠ ⎝ ⎠

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Modeling Modeling

Laser exposure along the X

Laser exposure along the X-

Axis defined as

Axis defined as

2 2

2

2 ( , )

p

z y D w s

P E y z e e W V π

− −

⎛ ⎞ = ⎜ ⎟ ⎝ ⎠

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Focused laser spot Focused laser spot scanning method scanning method

(patent pending No 1847/MUM/2007) (patent pending No 1847/MUM/2007)

Laser beam

Linear scanning of mirrors in

th di ti f th l b

300 M1 Lens M2

the direction of the laser beam axis

ADVANTAGES:

☺ Uniform spot characteristics

(i.e. constant spot size and uniform intensity profile)

☺ Virtually no limit on range

M2 Focal Plane z x y

☺ Virtually no limit on range ☺ Improved resolution ☺ Higher speeds possible

Development of new Development of new scanning MSL system scanning MSL system

(Optical system) (Optical system)

M4 M3 M2 M1 M1 Ar+ Ion Laser AOM Pinhole M4 Lens

Focal plane z x y

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Flexure Mechanism Flexure Mechanism

Concept

To implement idea with

To implement idea with nanometric nanometric scanning scanning resolution innovative use resolution innovative use

f double parallelogram
f double parallelogram

flexure mechanism and flexure mechanism and mechatronic mechatronic system system around it around it

Parasitic error

around it around it

Ref: Arun Shourya, Phd Thesis, MIT

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XY Flexural XY Flexural Mechanism Mechanism

(Photographic View) (Photographic View)

Actuators Optical Encoder

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Opto Opto-

mechatronics

mechatronics System: System: Subsystems

Subsystems

Scanning MSL system

(Photographic View) M3 Pinhole XY Flexural Mechanism Ar+ Ion Laser M4 Laser Remote Module Z-Stage AOM

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Experimental Experimental investigation investigation

Exact focus is determined by two

Exact focus is determined by two methods methods

– Using beam Using beam profilometer profilometer Using beam Using beam profilometer profilometer – By curing experiment By curing experiment

Minimum spot size measured

Minimum spot size measured using beam using beam profilometer profilometer is less is less than 40 than 40μm (Coarse tuning) m (Coarse tuning)

Minimum cured width achieved is

Minimum cured width achieved is 6.14 6.14μm at 8.55 mm distance from m at 8.55 mm distance from lens holder (fine tuning) lens holder (fine tuning)

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15 3D 3D Microfabrication Microfabrication

Distortion and Fabrication Resolution Analysis (Fabrication of Distortion and Fabrication Resolution Analysis (Fabrication of Circular Holes of different Sizes) Circular Holes of different Sizes)

C4 C5 C6 C7 C3 C2

C1

A CAD Model A 1 2 3 4 5 6 7 Fabricated Structure

Fabrication of Circular Holes

Sr. No

1 2 3 4 Average Model Error % Distortion C1 508.07 508.07 505.26 505.26 506.665 500 6.665 1.33 C2 409.82 404.21 404.21 401.4 404.91 400 4.91 1.23 C3 304.39 307.19 305.96 308.77 306.5775 300 6.5775 2.19

Larger Size of holes are fabricated accurately than the smaller size holes Larger Size of holes are fabricated accurately than the smaller size holes

C4 204.91 207.72 202.11 207.72 205.615 200 5.615 2.81 C5 153.35 154.39 159.39 157.19 156.08 150 6.08 4.05 C6 105.75 108.27 109.47 109.47 108.24 100 8.24 8.24 C7 61.85 55.45 61.75 57.85 59.225 50 9.225 18.45

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3D 3D Microfabrication Microfabrication

Distortion and Fabrication Resolution Analysis (Fabrication of Distortion and Fabrication Resolution Analysis (Fabrication of Solid Circles of different Sizes) Solid Circles of different Sizes)

C4 C5 C6 C7 C3 C2 C1 CAD Model Fabricated Structure

Sr. No

1 2 3 4 Average Model Error % Distortion C1 494.04 496.84 496.84 497.48 496.3 500

3.7
0.74

C2 395.79 398.6 401.4 398.8 398.6475 400

1.3525
0.34

C3 297.54 297.54 300.1 296.85 298.0075 300

1.9925
0.66

Fabrication of solid circles

C3 297.54 297.54 300.1 296.85 298.0075 300 1.9925 0.66 C4 196.48 197.85 197.45 200.1 197.97 200

2.03
1.02

C5 148.77 146.87 147.85 147.15 147.66 150

2.34
1.56

C6 97.25 96.25 97.25 97.65 97.1 100

2.9
2.90

C7 47.58 44.95 45.25 47.85 46.4075 50

3.5925
7.19

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Fabrication of single Fabrication of single layer micro layer micro-

structures

structures

Circular features Line Scanning of 6 μm width Text Writing within 800 μm Gear with diameter 500 μm Complex Shape

Concentric Circles 100, 250, 500 and 1000 μm with width 26 μm

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Slicing, Scan Slicing, Scan Path Generation Path Generation

In house software

3D CAD Model Slicing data Scan path Generation data Laser ON/OFF conditions XY focused spot positions

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Fabrication of Fabrication of multilayered micro multilayered micro-

structures

structures

1 mm 1 mm Square tank with 1mm outer size Square tank with 1mm outer size 800 800 μm inner size wall thickness of m inner size wall thickness of 200 200μm Height of 500 m Height of 500μm 10 layers m 10 layers Pyramid with 1mm size fabricated inside a tank of size 1.6mm Height of the structure is 750μm 15 layers 1 mm 1 mm

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More Fabricated More Fabricated Microstructures Microstructures

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More Fabricated More Fabricated Microstructures Microstructures

1mm

Large-range, high- resolution components fabricated at high speeds

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Cell Growth in Cell Growth in Confined Wells Confined Wells

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3D Fabrication 3D Fabrication Capabilities Capabilities

1mm

High aspect ratio microchannels

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Microstereolithography Microstereolithography

Limitations

Smooth 3D surfaces difficult to produce;

Smooth 3D surfaces difficult to produce; stepping effects will always be present stepping effects will always be present

Mass production of several components

Mass production of several components is another challenge is another challenge is another challenge is another challenge

Extremely small features challenge to

Extremely small features challenge to produce (Topic of current research) produce (Topic of current research)

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Conclusions Conclusions

Microstereolithography: process details Microstereolithography: process details Mainly a process for true 3D structures of Mainly a process for true 3D structures of polymer and ceramic materials polymer and ceramic materials Limitation about the size of the feature Limitation about the size of the feature and mass production and mass production

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Thank You Thank You

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