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Printing electronic devices

School of Engineering and Science

Amare Benor

22.11. 2005

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� Motivation

� Different printing techniques

� Microcontact printing

� Self assembly process

� Selective surface wetting

� Applications

� Summary

Outline

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Motivation

Macroelectronicsmanufacturing needs a paradigm change:

�Photolithography�Printing:Flexible substrates0

10

20

30

40

50

60

2000 2001 2002 2003 2004 2005 2006 2007

mar

ket s

ize

($B

illio

n)

The display market is big and getting rapidly bigger

DisplaySearch data

Big LCD TVs are coming …..30”, 40”, 50”, 60”….

Gen 5 → Gen 7 fabs. Substrates are getting really large

Philips

Philips

Vision!

Alternativeprocessing Technologies:

Roll-to-Roll, Sheet vs Batch Processing

Learning form Printing Processes

Motivation

Different Printing Technologies

Offset printing Microcontact printingInkjet printing

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Photolithography and Microcontact Printing

Microcontact Printing

Advantages:Low cost, Additive process (mostly)High resolutionApply to non-planar surfaces/ConformalUses a variety of materials

Disadvantages:Emerging TechnologyRegistration problems

Photolithography

Advantages:High resolutionVery good registration/alignmentMass production

Disadvantages:High costSubtractive processLimited by optical diffraction

resolution ~ 100 nm

photo resist

UV light

Substrate

Mask

� soft stamp

� conformal contact,

� molecules wet

� resolution ~ 35 nm

Microcontact Printing

Advantages:Low cost, Additive process (mostly)High resolutionApply to non-planar surfaces/ConformalUses a variety of materials

Disadvantages:Emerging TechnologyRegistration problems

Advantages:Low cost Additive process (mostly)High resolutionApply to non-planar surfaces

Disadvantages:Emerging TechnologyRegistration problems

Microcontact Printing

resolution ~ 35 nm

soft stamp

moleculesSubstrate

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Basic elements of �CP:

� Stamp

- made of silicon based elastomer

(poly-dimethylsiloxane, PDMS)

- conformal contact with substrate

� Self assembled monolayers (SAMs)

���� for different applications

(functionalize surface,etch resist,

selective deposition, ...)

Microcontact Printing (�CP)

Principles of �CP (one of the printing techniques)

Substrate

Master

Coating stamp with SAM

Transfer of SAM

Patternformation

Manufacturing of the stamp

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Self Assembly Process

Self Assembled Monolayer as Resist (Whiteside’s Approach)

• Thiol molecule printed on metal

surface (gold, silver)

• Thiol used as etch resist

• Interface chemistry is essential

• Resolution: < 100 nm

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Functionalizing Surfaces

• Printing of OTS (octadecyltrichlorosilane) molecules on silicon or glass

• Hydrophilic/hydrophobic pattern is formed

• Stamped region ���� Hydrophobic

• Unstamped region ���� Hydrophilic

• Reactive site on unstamped region

Hydrophobic SAMs

Eg. OTS, ...

Stamped region

(Hydrophobic)Unstamped region

(Hydrophilic)

OTS (CH3(CH2)17SiCl3) SAMs

Self Assembly Process

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Selective Surface Wetting

Patternable polymer:

Resist, Polymer, Semiconducting polymer

Dipcoat polymer

UV exposure to remove OTS SAMs

Patterned Polymer

Patterned OTS SAMs

General approach to pattern polymer and metal

100 µµµµm

S D S D

F8T2 TFT fabricated by micro-contact patterning [M. Chabinyc et al.]

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Selective Surface Wetting

Metal pattern:

Ti, Au, Pt,...

After e-beam evap. of (Ti/Au) and lift off

E-beam evap. of (Ti/Au)

Patterned Polymer

General approach to pattern polymer and metal

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Resolution (~ 20 �m)

Application: Passive Components (Coils)

RFID (Radio Frequency IDentification) Tags:

� Chip

� Antenna/coli

Radio Frequency (RF) coils

PMMA

OTSAu

Stamp

50 �m

50 �m50 �m

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Electrodes and Interconnects

20 �m 20 �m 10 �m

Electrodes with 20, 10 and 5 �m gap

Resolution (~ 10 �m)

Application: Interconnects and electrodes

• Smallest features size depends on the geometry of the features.

• The resolution is limited by the selective wetting rather than the micro contact printing.

Dielectric

Gate

Highly doped silicon

Source

Org. Semicon.

DrainVD

VG

VS

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DiscussionEffect of film (PMMA) thickness and geometry on dewetting

Homogeneous surface3/2)(Calh c=

glc ρ

σ=

Heterogeneous surface3/1)(CaWh =

where, σ

µUCa =and

σ = surface tension

ρ = surface density

µ = viscosity of the liquid

U = withdrawal speed of the substrate

As h increases ���� budging effect and pattern distortion

PMMAOTS

w

w

substrate

h

Top view

Side viewDifferent geometry can result different resolution

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Summary� Micro Contact Printing (µCP) is a promising technique for applications in organic electronics and photonics devices

� µCP of SAMs allows for surface energy modifications

� A combination of �CP and dewetting can be used used a universal patterning process

� Microcontact printing and dewetting can be used to pattern polymers

� Microcontact printing and dewetting was used for to pattern metal films for interconnects, rf coils and OFET electrodes

� The film thickness is crucial parameter to get the required width of a patterned polymer