biobarrier carcia euro cvd kinsale 2011 ed

8/12/2019 Biobarrier Carcia Euro CVD Kinsale 2011 Ed

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ALD ULTRA-BARRIERS FOR ELECTRONIC

APPLICATIONSSTRATEGIES AND

IMPLEMENTATION

P.F Carcia* , R.S. McLean, B.B Sauer, and M.H. Reilly

DuPont Research & Development, Experimental Station,

Wilmington, DE 19880-0400 USA


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Motivation

Enable flexible electronics on

polymer substrates:

-OLED Displays

-OLED Lighting-Organic transistors and solar

cells

-CIGS solar cells

18.7%efficiency

Motivation


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Need Moisture Barrier Coating

Most organic devices are extremely moisture sensitive and

need a packaging strategy to protect from moisture-driven

degradation.

However, flexible polymer substrates are highly permeable to

all atmospheric gases, whereas glass is impermeable.

What is needed is a barrier coating on flexible polymers thatessentially excludes atmospheric gases, comparable to glass.

This barrier coating must be pinhole-free, defect-free, and

dense.A barrier coating grown by atomic layer deposition (ALD) is as

close to perfect as one can practically achieve.


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10

10-1

10-3

10-5

WVTR/OTR

g or cc/m2/day

Thin Film PV (CIGS)

OLEDs

Polymer films

PET, PEN,FEP

Traditionalpackaging films

Range of Barrier Requirements

LCD

Need an Ultra-barrier technology to meet needs for OLEDs and

and CIGS solar.


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Ref. A. Dameron (NREL)

Most sensitive commercial instrument for WVTR

1-3 days measurement time


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WVTR measurement using Ca-test

Light

PEN or PET

Barrier f ilm

Epoxy

Ca (50 60 nm, semi-transparent)

Glass Substrate

14

16

18

0 1000 2000 3000

%T

t(hr)

60 C/85% RH

38 C/85% RH

oxide barrier/HS-PEN-5mil

WVTR~1.7x10-5

g/m2/day

WVTR~6.5x10-5

g/m2/day

Ca + H2O CaO + H2

or

Ca + 2 H2O Ca(OH)2 + H2

Both CaO and Ca(OH)2 are transparent

WVTR (CaO)

D(CaO)/t

m(H2O)/m(CaO)

%

T

ALD Al2O3 at ~120 C

10x more sensitive than MOCON


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How good is a single ALD barrier coating?


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Outline

How important is the temperature of the ALD process for

ultra-barrier properties.

Does pre-treatment/cleaning of the substrate affect ultra-

barrier properties

plasma etching

How does substrate surface chemistry affect ultra-barrier

properties.

Raw polymer side

Slip-side


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Leakage current density and breakdown voltage in ALD

Al2O3 depends of synthesis temperaturebarriers?


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Moisture permeation in ALD Al2O3 depends on synthesis T and film

thickness; failure (pinholes) is abrupt, but prior changes track glass.

(1200 hr at 38 C/85% RH +500 hr at 60 C/85% RH)

Polymer PET surface

Films grown at higher T and

thicker are more stable.


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Permeation model*

Moisture permeation in ALD Al2O3 is not due to

pinholes.

Permeation is attributed to diffusion of molecularlydissolved H2O along defect clusters (-OH) in the Al2O3amorphous network. ([H]-content increases for low ALD synthesis)

Permeation breakthrough occurs when the defectclusters percolate the ALD barrier film thickness.(analogous to electrical breakdown)

Postulate the time-to-failure, tf=t0(H/kT-d0/d), whereH is ~ bonding energy between H2O and

oxide/hydroxide defect clusters, and d0 ~ threshold

barrier thickness.*Carcia et al. Appl. Phys. Lett. 97, 221901 (2010)

Pfeffer and Ohring, J. Appl. Phys. 52, 777 (1981)


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Effect of plasma-etching PET surface


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contact angle, c =62.2

for PET

Etched PET surface is more hydrophil lic

c =23.6

Dark region (phase image) is

softer amorphous segmentbetween harder (light)

crystalline domains.

Etching preferentially removes

softer amorphous segment.

Ar-etching at -50 V(10 min)


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Lower moisture permeation for thinner Al2O3 on etchedPET.

Hydrophilic surface may

present a more reactive

surface for TMA

adsorption--improved

nucleation


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Effect of surface chemistryraw polymer versus

coated slip-side of PET polymer


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Coated slip-side of

PET is rougher andabsent the

crystalline fibril

features of raw

polymer surface.

Comparison of slip and raw polymer sides of PET


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Barrier performance is superior for ALD on raw polymer side.


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ALD Barrier Application to CIGS Solar Cells


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85 C/85% RH

Environmental Chamber

Measured at IEC (U. Delaware)

Encapsulated PV cell

2mil FEP

25 nm ALD

Al2O3 on

uv-PET

encapsulant

CIGS cellGlass

Change in efficiency of CIGS ~2% in 1032 hr at

85

C/85% RH +solar illumination

adhesive

8

9

10

11

12

13

14

0 10 20 30 40

85 C/85 % RH +illumination 1032 hr

Effic

iency(%)

t(days)

1xALD-uv-PET

2xALD-uv-PET

Damp Heat Test Results for CIGS


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Summary

For best barrier performance: thicker films and higher ALDgrowth temperature are preferred.

Polymer surface pre-treatment, e.g. plasma etching, improvesbarrier properties.

The two sides of a polymer film are more often chemicallydifferent, and ALD growth may produce better barrier

properties on one side.

ALD barrier films are a promising candidate for a transparent,

flexible front sheet for CIGS solar cells.


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biobarrier carcia euro cvd kinsale 2011 ed

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