Discusses about Microsystems Technologies ,Micro Stereolithography.Basic concepts and terminology such as Selected traditional micromachining photolithography and mask design, wet and dry bulk etching, bonding, thin film deposition and removal, metallization, sacrificial processes, other inorganic processes, electroplating

1. Microsystems Technologies
Basic concepts and terminology
Selected traditional micromachining photolithography
and mask design, wet and dry bulk etching, bonding, thin
film deposition and removal, metallization, sacrificial
processes, other inorganic processes, electroplating
Polymer techniques (not neccesarilly exact order()
polymer materials and basics, thick-film polymers, soft
lithography and multiple methods of micromolding,
stereolithography, LIGA

2. Micro Stereolithography (μSL)
Arapid prototyping microfabrication technique that involves layer by
layer photopolymerization of resin to produce 3D microstructures.
By exposing multiple layers, one on top of each other, complex 3D
shapes can be realized.
Book: Microstereolithography and other fabrication techniques for 3D MEMS, V.
K. Varadan, et.al., John Wiley & Sons, 2001.
Article: “Mail Order Microfluidics”, A.K.Au, et.al., Lab on a Chip, 2014, p 1294.
Types
Scanning method
Scans across each layer line by line using a laser to
photopolymerize one small “spot” at a time.
Projection method
Scans each layer all at once using projection of uv-light
through a (dynamic) mask.

3. Micro-Stereolithography
μSL fabrication steps
1.
2.
CAD file generation
Slicing 3D model into series of closely spaced horizontal planes
(layers) representing the 2D (x-y) cross-sections
2D model translation into numerical control code for laser or
dynamic mask
3.
4. Photopolymerization of successive layers to form the 3 the 3D
(beam or projection)
z
y
x
object by building it up one layer at a time (z-dir)
layers
Layer-by-layer SEM photograph
photopolymerization
CAD drawing

4. Micro-Stereolithography
μSL fabrication steps
1.
2.
CAD file generation
Slicing 3D model into series of closely spaced horizontal planes
(layers) representing the 2D (x-y) cross-sections
2D model translation into numerical control code for laser or
dynamic mask
3.
4. Photopolymerization of successive layers to form the 3D
Object by building it up one layer at a time (z-dir)
(beam or projection)
z
y
x
layers
Layer-by-layer SEM photograph
photopolymerization
CAD drawing

5. Micro-Stereolithography
Most common is HDDA:
1,6 hexanediol diacrylate.
Acrylates
Urethanes
Epoxies
Vinyl ethers
Resolution and
Typically not
minimum feature
great (even still; see 2014 article)
Even using expensive equipment
ଛ min. resolutions on order of 30 μm or
ଛ smallest features on order of 100 μm
so
or so
Materials for μSL

6. Micro-Stereolithography
cellular
scaffolds Examples and applications
Fluidics

7. Two-Photon Polymerization (2PP)
•Principle similar to stereo-lithography (SL) technique
•Provides much better structural resolution and quality
•Curing: 2PP uses near-infrared (IR) laser pulses
whereas μSL uses ultraviolet (UV) laser radiation
•Photosensitive materials are usually transparent in the infrared,
highly absorptive in the UV range
•initiate polymerization with IR laser pulses within the volume
and fabricate 3D structures, where as UV is surface/planar
Courtesy Laser Zentrum Hannover e.V

8. 3D Printing
3D printer general fabrication steps
1.
CAD file generation
2.
Slicing 3D model into series of closely spaced horizontal planes
(layers) representing the 2D (x-y) cross-sections
3. 2D model translation into numerical control code for extruders
that extrude as lines of polymer (1 to 4 typically) from
filament
the
4. Extruding of polymers and fusion of the printed lines
Typical polymers (thermoplastics)
acrylonitrile butadiene styrene (ABS)
polycarbonate (PC)
polylactic acid (PLA)
high density polyethylene (HDPE)
PC/ABS
polyphenylsulfone (PPSU)
polyurethane (PU) based elastomers

9. 3D Printing
Resolution and minimum feature
Typically not great, but getting better
Equipment not so expensive though to get
೦ min. resolutions on order of 30 μm or so
೦ smallest features on order of 50 μm or so
Example application in microfluids:packaging
article (thanks Kimball!): O.H.
Paydar, et.al., Sensors and
Actuators A, 2014, p 199.
made using Makerbot in my lab

10. Micromolding
Micromold inserts
Micro injection molding
Micro hot embossing (compression molding, stamping)
Soft lithography
Casting of elastomeric structures
Micro transfer molding
MIMIC (micro molding in capillaries)
Micro contact printing

11. Micromolding: Common Methods and Materials
Molding method Molding
material(s)
Mold insert
material(s)
Injection molding Thermoplastics Nickel, silicon, SU-8,
NiCo,WCo, steel,
ceramic powder
Hot embossing Thermoplastics Nickel, silicon, NiCo,
WCo, steel
Soft lithography:
casting
Thermosets,
elastomers
SU-8, silicon, silicon
dioxide or nitride
Micro transfer molding
and MIMEC
Thermosets PDMS
Micro contact printing Self-assembled
monolayers
PDMS

12. Micromolding
Micromold insert:general characteristics
Low mechanical stiction and friction
Vertical or positively sloped sidewalls (no undercut)
Avoid surface oxidation
chemically inert, smooth surfaces, homogeneous materials,
free of sidewall defects
Example micromold insert methods
a)
b)
c)
d)
e)
f)
CNC physical milling
Laser ablation
X-ray litho and e-form
Si etching
SU-8
EDM (electro
discharge machining)

13. Micro Injection Molding
High-temperature micromolding technique using inserts
Typical process
1.
2.
3.
4.
5.
Mold inserts are placed into molding chamber
Air is evacuated out leaving the chamber under vacuum
Polymer pellets are heated above their melting point Liquid
polymer is injected into the mold
Pressure and temperature holding to ensure good filling of
high-aspect ratio structures
Cooling
Demolding
6.
7.

14. Micro Injection Molding
Typical specs
1.
2.
Injection pressure set 500 – 2000 bar (high!)
Molding temperatures above glass transition, below
degradation
Minimum wall thickness of 20 μm
High aspect ratios (20+)
Structural details down to 1 μm (typical)
3.
4.
5.
Materials
PMMA
PSU
PC
PA
POM
PEEK
COC
and temperatures for μIM
polymethylmethacrylate
polysulfone
polycarbonate
polyamide
polyoxymethalene
polyethylethylketone
cyclic olefin polymer
(in ºF)
200-250
360-400
240-260
220-280
180-210
370-400
260-310

15. Micro Injection Molding
Examples and applications
microchannels
AMANDA micropump
cell chip LILLIPUT Microfluidic
microneedles
ChipShop

16. Micro Hot Embossing
High pressure micromolding technique by compressing a
softened polymer against a mold insert
Also called stamping or compression molding
Typical process
1.
2.
3.
Mold inserts and polymer are placed into molding chamber
Chamber is placed under vacuum
Polymer thick film and mold are heated to just above glass transition
temperature ଛ much lower temps than injection molding
4. Polymer thick film is pressed to fit into themold insert using
pressures
Tool and substrate are
cooled
(Re-embossing),
demolding and part
extraction
high
5.
6.

17. Micro Hot Embossing
Force, temparature in arbitrary units

18. Micro Hot Embossing
Typical specs
1.
2.
3.
4.
Typical pressure = 25 – 30 bars
Submicron features possible
Good aspect ratio possibilities (10-20:1)
Simple and inexpensive
Materials and glass transition temperature
Abbreviation

19. Micro Hot Embossing
Examples and applications 0.8 μm PMMAfeatures
Microchannel arrays from DRIE silicon mold
150 μm
Nano Devices and
Systems Research
biodegradable
microneedles With fiber optics 50 μm
Channel

20. Soft Lithography: PDMS Primer
The “soft” in “soft lithography”: PDMS
Poly dimethyl siloxane (“silicone rubber” elastomer)
Good reference: Xia and Whitesides, SoftLithography, Annual
Review Materials Science, 28 (1998) 153-84.

21. Soft Lithography: PDMS Primer
Characteristics of PDMS
1.
2.
Good chemical stability
Not particularly hydroscopic (does not swell with humidity),
however, many organic solvents will swell PDMS
High gas permeability (for good or bad()
Good thermal stability (up to 180 C)
3.
4.
5. Good thermal insulator (thermal conductivity 0.2W/mK, thermal
expansion 310 μm/mC)
Optically transparent down to 250 nm
Durable
Surface properties can be readily altered using plasma for
sealing to other PDMS, silicon, silicon nitride, PS, PE
Readily available, easy to work with
Highly elastic (can be good or bad); E = 750 kPa
Good insulator; breakdown voltage 2x107 V/m
Shrinks about 1% on curing
Nontoxic and biocompatible
6.
7.
8.
9.
10.
11.
12.
13.

22. Soft Lithography
Casting PDMS
Master can be silanized by
exposure to vapor:
CF3(CF2)6(CH2)2SiCl3
for 30 minutes
This attaches chlorosilane to any
dangling surface bonds (e.g.,
OH), so they they will not
attach to PDMS
Master is usually silicon or SU-8
PDMS structures can be used
directly, for another
soft lithography
process, or machined
Cure (e.g., 65C
2 hours)
for
using other methods
Features down to 30nm

23. Soft Lithography
Molded tubing into PDMS
Tubing is also silicone (Tygon)
Soft lithography potential problems
Sagging
Shrinkage (1%)
0.2<h<20
0.5<d<200
0.5<l<200
(microns)
Lateral displacement
Sticking to master
(pairing)
Holes higher aspect ratio
than towers possible

24. PDMS DeviceApplications
Applications in PDMS
Biochemical assays
Capillary electrophoresis
Cell
counting and sorting
Cell
growth
Cell
studies using sheath
mixer
flow
retina
Chemical reactions
Control of fluid flow
cells
Detection of biological species
Mixing
O-rings
Genomics
Liquid chromatography
Mass spectrometry
Optical components
Implantable packaging
Hybrid systems
o-rings
hybrid
Goodreview: Sia and Whitesides, Electrophoresis 24 (2003), 3563-76.

25. Micro Transfer Molding
Process
Curing is either uv or
thermal
Typical materials: PU,
epoxy, suspensions
(sol gel)
Feature sizes of a few
microns
Can build layers for
multilevel structures
Basic Process Multilayer
Polyurethane (PU):
thermosetting

26. Micro Transfer Molding
Applications

27. Micro Molding in Capillaries
Basic process
PDMS mold is pressed tightly to substrate
surface
Common substrates: silicon, glass
Liquid resin fills channels by capillary action
Typical structure sizes:
350nm to 50 μm wide
a few microns deep

28. Micro Contact Printing
Introduction
Uses a PDMS “stamp” to apply another material (self-assembled
monolayer (SAM), biomolecules such as proteins)
to the substrate in a pattern
Stamp is contacted to substrate, which can be coated
oxide or metal layers (e.g., Au, Ag)
with
Patterned material can then act as a resist for etching
selective deposition
or
Features as small as 300 nm can be realized
Difficult to pattern large area surfaces
Can pattern non-planar surfaces (e.g., cylinders)

29. Micro Contact Printing
First, make PDMS stamp using
molding as we discussed
Next apply “ink” which contains
the SAM molecules or
biomolecules in
(e.g., ethanol)
another solution
apply “ink”
“ink”
Print the SAMS
that have better
or biomolecules
affinity to
substrate surface than PDMS
selective deposition selective removal
Use the monolayer directly or
for selective etching or
deposition of another material

30. Micro Contact Printing
Self-assembled monolayers
Alkanethiol
CH3(CH2)n-1SH
alkane is a hydrocarbon that is entirely
thiol is a sulfhydryl group, SH
single bonded, CH3(CH2)n-1
Layer thickness is controlled by the number of methyl groups, n
SH has a selective affinity (likes to attach to) gold in particular
Easy surface adsorption onto gold from solution
Hydrophobic and not inert to cell/protein attachment on terminal end

31. Micro Contact Printing
(Other SAMS)
alkylsiloxanes on hydroxyl terminated surfaces (e.g., silicon dioxide
and other glasses)
SAMs used for making surface micromachined polysilicon
hydrophobic to prevent stiction
SAMS uses
SAMs can be used directly as a “resist” or used to modify surface
properties for additional molecular attachment
Not resistive to RIE, only resistant to certain wet etching solutions
(see Xia and Whitesides)
Can also use SAMS for selective deposition; material will either
attach selectively to SAMS template (polymers) or nucleate
where there are no SAMS (CVD metal)

32. (Micro Contact Printing)
(Examples of SAMS as a “resist”)

33. Micro Contact Printing
Resist patterning on non-planar substrates
Can easily pattern on cylinders
Flexible PDMS can be deformed
around non-planar substrate
Can thus pattern metal on cylindrical
objects such as glass fibers

34. Micro Contact Printing
μCP patterned metal for electrodeposition
After metal wet etching, electroplate
Can also be used for non-planar substrates
Make free-standing patterned metal
by etching away substrate (e.g., glass
tube)

35. Micro Contact Printing
Examples and applications for μCP plus e-plating
Microcoils for micro nuclear magnetic resonance (μNMR),
microsolenoids, and microtransformers; microstents
microstent
solenoid
ferromagnetic wire
small insulting tube
transformer

36. Micro Contact Printing
Biomolecule and cell applications
Direct biomolecule stamping (e.g., proteins)
Attachment of cells or biomolecules to SAMS
Potential uses: microarrays for biochemical analysis
cell manipulation and research
Hippocampal neurons on poly
lysine (protein) printed surface

37. Micro Contact Printing
(brain., spinal cord cells)
Endothelial cells selectively
cultured on SAMs on Au coated
substrate (chemically alters EC
function)

38. Thank You
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