AIMCAL October 2008

Vacuum Deposition of High Performance Gas Barrier Materials

for Electronics Applications

Hélène SuttleDPhil Research Student

Department of Materials -University of Oxford

AIMCAL Fall ConferenceOctober 2008

AIMCAL October 2008 2

OUTLINE

Description of Barriers• What they're made of• Where they're used• Requirements of barriers

What we're making• Substrates – PEN and Smoothing layers• Coatings• RF/DC Sputtering

Sample testing• Thickness• Refractive Index• Permeation• Surface Morphology • Transparency• Surface chemistry

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Barrier Layers

H2O O2 CO2

Polyethylene naphthalate (PEN)

BARRIER LAYER

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Barrier Layers for Electronics

WVTR(g/m2/day)

100 10-1 10-2 10-3 10-4 10-5 10-6

Food PackagingPharmaceuticals

OTFT

Vacuum InsulationPanels

DSSC Excitonic PVs

OLEDsBARRIER TYPE

Component Lifetime

Tolerance

Mechanical Properties

Process Speed & Cost

Transparency

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Objective

Deposition of acrylate and Al2O3 onto PEN for transparent gas barrier applications

This is achievable by using• High quality polymer substrate• Dense Al2O3 layer• Flash-evaporated acrylate layer for smoothing and separation of any multiple layers.

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Design of High Barrier Layers for Electronics

Decrease density of macrodefects• Smooth substrate• Processing Control

Extend time before equilibrium permeation (lag time)• Thick/multiple layers• Decrease diffusivity

At equilibrium• Decrease diffusivity and solubility

• Dense coating• Chemistry

AlOx Coating

PEN

AlOx Coating

PEN

AlOx Coating

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Oxford Web Coater: Exterior

• Cooled single drum• Multiple layers can be deposited in-line or sequentially.• Film width = 350mm, Thickness 7 to 24μm• Web speed up to 300m/min

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• Plasma treater• Dual magnetron sputter deposition• Evaporation• Polymer coating by flash evaporation and electron beam cure

Oxford Web Coater: Deposition

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DC/RF Sputtering

•Power to magnetrons supplied by a DC or RF power supply

•RF sputtering avoids target charge build up – pulsed DC must be used to avoid this

•RF power is twice as expensive per unit thickness as DC power

•DC sputtering allows better control of thickness and is more stable than RF

AIMCAL October 2008

Substrate Materials

PET PEN

Upper Processing Temperature (deg C) 150 180-220

Glass Transition Temperature (deg C) 78 120

Continuous Use Temperature (deg C) 105/130 160

Young's Modulus @ 20 deg C 4GPa 5GPa

Young's Modulus @ 150 deg C 1GPa 3 Gpa

Tensile Strength (MD) 195MPa 200MPa

Moisture Pickup @ 20 deg C 40% RH 1000ppm 1000ppm

Shrinkage in MD @150 deg C after 30 mins 0.10% 0.05%

Water Vapour Transmission Rate (g/m^2/day) 20 3.6

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Al2O3 deposition - Sputtering

0 10 20 30 40 50 60 70 80 90 1000

50

100

150

200

250

300

Al2O

3 thi

ckne

ss (n

m)

Deposition time (min)

PoisonedMetalPoisoned (oxidised) target

• very low sputtering rate (2.7 nm/min) • very poor H2O(g) barrier properties

1-1.3 g/m2day

Metal target• high sputtering rate (17.5 nm/min) • very good H2O(g) barrier properties

<0.003 g/m2day

50 m/min; 1.92kW O2 = 5 sccm; Ar = 95 sccm

RF Sputtering - Hysteresis

0

100

200

300

400

500

600

0 5 10 15 20 25

Oxygen (sccm) per 100sccm Ar

Volta

ge

Decreasing Oxygen fromMaximum

Increasing Oxygen from0sccm

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Oxygen Delivery

Oxygen is introduced in different locations. • Sputter zone• Adjacent to drum (outside Sputter

zone)• Main chamber

Nature of oxidation is different in each case• In sputter zone, oxidation occurs

prior to deposition or at deposition• Outside sputter zone oxidation

occurs after deposition

Oxygen introduced outside sputter zone is less likely to poison the target

Sputter Zone (Original Oxygen

Delivery here)

Alternative Oxygen Delivery Location

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Appearance of Coated Films

PEN 30 sec 20 min 20 min

Mirror Laser Diode

Cantilever and Tip

Feedback

XYZ Piezo Scanner

Image

Optical deflection sensorAFM

AIMCAL October 2008

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Film Transparency

UV-vis Spectra

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

0 100 200 300 400 500 600 700 800 900 1000

Wavelength (nm)

Abs

orba

nce

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Al2O3 deposition

•Thickness is measured using single wavelength ellipsometry•Refractive Index can also be measured

- Stoichiometry & Density

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#2.1

NameO 1sC 1sF 1sAl 2p

Pos.530.799284.799683.799

73.799

FWHM4.541874.784165.031184.21886

Area3925921.2

643659.778496.9

459364.1

At%53.6623.230.71

22.40

O 1

s

C 1

s

F 1s

Al 2

p

x 105

2

4

6

8

10

CPS

1000 800 600 400 200 0Binding Energy (eV)

Film Stoichiometry

X-ray Photoelectron Spectroscopy (XPS)

Peaks show presence of Aluminium, Oxygen and Carbon

Average stoichiometric ratio is AlO2.2C1.1

Oxygen content is affected by sputtering type – RF oxygen content is lower in samples produced to date

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Permeation Measurement

There are several permeation measurement techniques

Mocon ® permatran testing uses an RH sensor to measure the quantity of water travelling across the barrier film

Detection levels are ~5x10-3g/m2/day H2O(g)

RH SENSOR

TEST FILM

WATER

PURGE GAS IN PURGE GAS OUT

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Calcium Test

FLEXIBLE SUBSTRATE

SPUTTERED GAS BARRIER LAYER

GLASS PLATE

EVAPORATED CALCIUM

EPOXY

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Calcium TestCalcium is oxidised (white) by H2O passing through barrier

The quantity of water moving across the barrier is calculated by comparing thereacted calcium to unreacted metal at different time intervals

48 Hours

240 Hours

508 Hours

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Permeation Measurement

CRYSTALLINE POLYMER

GLASSY POLYMER

DEFECTS IN BARRIERS

INTERFACE

• A series relationship exists for multiple layers…1/Ptotal = 1/P1 + 1/P2 + 1/P3 + …

• P = P0 exp (-EA/RT)P: Transmission rate P0:constant related to the gas and barrier materials respectively

• Defect dominated layers do not contribute to activation energy

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Activation Energy, EA

• Defect dominated layers do not contribute to activation energy

• EA (Composite) ≅ EA (Polymer):•Unhindered flow through defects.

• EA (Polymer) < EA (Composite) < EA(Barrier Layer):

•Hindered flow due to sub-nanopores or coating matrix?•Chemical interaction with the coating?

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Barrier Layer Defects

‘Lag time’ for water to penetrate each layer of a barrier film dependent on• Layer thickness• Diffusivity

Multiple Layers• Permeation dominated by

diffusion through nanodefects

• Long time to reach equilibrium permeation

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Conclusions

Reactively sputtered Aluminium Oxide has been deposited on PEN filmsRF and DC power supplies have been comparedTransparent films have been producedDefect free barriers (<0.001 g/m2.day WVTR) have been achieved with a single layer of Al2O3