biobarrier carcia euro cvd kinsale 2011 ed
TRANSCRIPT
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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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