Alf Smith *, David Bird, Andrew Cook, Steve Edge, Phil Hollis, Paolo

Ultra-barrier Encapsulation by ALD R2R
Processing for Flexible Large Area Devices
Alf Smith *, David Bird, Andrew Cook, Steve Edge, Phil Hollis, Paolo Melgari, Steve Spruce
Abstract
Ultra Barrier Deposition Systems
High barrier materials are required for the encapsulation of a wide variety of flexible large area devices; these include
printable electronics, OLED devices, OPV, thin-film inorganic PV to name a few. The level of barrier necessary varies
depending on the type of device, the required life-time, the materials used in fabrication and the environmental
conditions the device will be used in. Barrier encapsulation for devices not requiring any transparency; for light in (e.g.
PV applications) or out (e.g. OLED applications), can be protected relatively straightforwardly with the incorporation of
sufficiently thick metal foils (15-25micron) in polymer laminate structures. However, the clear barrier front sheet or
back sheet with edge seal, with sufficient barrier performance are much more difficult to achieve, especially for outdoor
applications (e.g. PV), where acceptable cost points and high levels of robustness are required.
CPI have deposited ultra-barrier single and multi-layer stacks by sputtering techniques in a 400mm-wide roll-to-roll
(R2R) sputter coater, depositing AlOx on PET and PEN substrates. In addition, single layer of AlOx on similar substrates
have been deposited by conventional (temporal) atomic layer deposition (ALD) in a batch system. The deposition
systems are shown below.
Introduction
The results for barrier layers of 30-40nm for
sputtering and 5-40nm for ALD systems are
shown in the table to the right (the sputtered
AlOx layers are deposited by reactive sputtering
from dual rotatable magnetron cathodes;
the ALD layers are deposited by sequential
introduction of Tri-Methyl Aluminium (TMA) and
oxygen plasma).
CPI is a Technology Innovation Centre located in the UK and part of the
High Value Manufacturing Catapult. The UK’s Catapult Innovation centres
work in the space between the discovery of an idea and the delivery of
a product or service to the commercial market. This is often referred to
as the “valley of death”. CPI works with clients and collaborators to bring
new products and processes to market quickly and efficiently, by offering
facilities and expertise that help reduce R&D risk and capital investment.
CPI’s National Centre for Printable Electronics is focusing on the
development, scale-up and commercialisation of printable and large area
electronic type applications such as OLED displays and lighting and PV
applications. CPI is equipped with an extensive range of open access assets
specifically chosen and developed to allow clients to understand how their
products and process perform under pilot manufacturing conditions.
Sputtered Barrier Stacks
Moisture Barrier (Extrinsic) g.m2.day-1 (Mocon, 38C, 90%RH)
Single AIOX Layer
5.10-2 - 5.10-1
Double AIOX Layer
4 - 6.10-3
Triple AIOX Layer
<5.10-4
ALD Single Barrier
AIOX (40nm thick)
<5.10-4
AIOX (5nm thick)
<5.10-4 (But less consistancy)
Ultra barrier levels are only achieved with
multiple sputtered layers; with single layer ALD deposition ultra barrier extrinsic performance can be achieved with layers
as thin as 5nm (although less consistency in production is achieved at present).
The intrinsic performance of an ALD barrier layer showing defects is shown below.
As part of the overall challenge to develop flexible larger area devices a
robust cost-effective flexible clear ultra-barrier technology is required
and CPI has undertaken a programme of development to investigate and
ultimately demonstrate and provided pilot production facilities.
For example, a typical flexible solar cell module is shown in the diagram below. This shows a high efficiency monolithically
interconnected thin film CIGS solar cell with the key encapsulation of a top clear barrier sheet and a back barrier sheet.
Additionally edge sealing is required to form the fully weather-able UV-protected flexible solar cells for outdoor PV
applications, including building integrated PV. Also shown below is a flexible OLED light element produced on CPI’s LACE
line and encapsulated with flexible clear barrier.
Bus-bar for Contacting
Monolithically Interconnected
CIGS Active Layer
WVTR
(g/m2/day)
Time in Damp Heat Test
(80°C, 80%RH)
PET
195
AI2O3
1.4x10-6
480 hours
3.7x10-2
640 hours
The pictures below show Ca-Test data, formed from transmitted-light stitched-microscopy images taken during aging
in 60°C, 90%RH damp heat aging trials. It can be seen that the rate of moisture permeation varies in a large range for
the defects present. Initial estimates suggest that 10% or less of the defects account for the majority of the moisture
permeation in most ‘large area’ samples. Control of these types of defects are key to the production of ultra-barrier films
with the chance of achieving ultra-barrier performance.
Diagram 1: Schematic Flexible CIGS Solar Cell Module
For grid parity flexible PV applications, the price point is particularly demanding.
Assuming 100 mW/cm2 solar irradiance and 15% module efficiency with a
target of 0.5 €/Watt peak, a flexible solar cell would not be more expensive
than 60 €/m2 (allowing for balance of systems costs). Solar cell modules require
encapsulation; the cost of them is estimated to be 25% of the total device cost,
with an estimated flexible clear barrier (including substrate) to be in the range
of 5-8 €/m2. This is very challenging for all barrier technologies, especially the
multilayer-barrier approach. For flexible OLED applications the price point is not
so challenging (10s €/m2) but the barrier performance requirement is very high
(10-6 g/m2/day moisture permeation or lower!).
0 Days
Single ‘Perfect’ Layer
Plastic Film
Single ‘Perfect’ Barrier Layer Approach
Multi Barrier Layer (Vitex Approach)
The schematic moisture permeation diagram shown below indicates that the multi layer approach only introduces a ‘lag
time’ for equivalent thick barrier layers. With requirements of 25 years for BIPV applications, the ‘lag time’ effect may not
be sufficient; the preferred solution being an ultra-barrier single layer, ideally as thin as possible to allow flexibility without
cracking and allowing higher line-speed production to be achieved.
Low Barrier
Medium Barrier
Polymer
Medium Barrier
H2O
(g/m2)
Lag Time
Lag Time
High Barrier
Time
CPI will be installing a 500mm-wide R2R spatial ALD coater from BENEQ (Finland) in the next few weeks. The first CPI
aim is to produce clear flexible ultra-barrier by R2R-ALD processing (including pre-and post-processing). The work will
be carried out in collaboration with the BENEQ and other interested parties. Further, CPI will develop R2R-ALD direct
encapsulation technology for a variety of flexible electronic applications. CPI believes R2R ALD deposition systems will
play an important role not only in ultra-barrier and encapsulation technologies, but also for conformal highly-dense films
for incorporation in a wide range of larger area ‘plastic’ electronic devices.
Initial coating trials have been carried out with promising results already achieved.
Low Barrier
Double Barrier
24 Days
Future R2R ALD Ultra Barrier Deposition Development
Barrier Layer
Plastic Film
4 Days
Initial trials for the encapsulation of flexible OLED devices produced on the CPI ‘LACE’ line have shown promising results
using single layer ALD ultra-barrier film encapsulants.
Inter-layer
Polymer
ALD Layer
The key development required is overcoming the effect of defects, rather than issues with the intrinsic barrier
performance of the ALD deposited layers; which will be addressed in CPI’s R2R ALD ultra-barrier programme (see below).
Back Side Encapsulation
H 2O
(g/m2)
Thickness
(Micons)
The intrinsic performance of the ALD barrier is shown in the photographs and table shown above-right. The photographs
show the ultra barrier samples after exposure to damp-heat conditions (80°C, 80%RH) and the table shows the
calibrated moisture permeation levels. The abrupt change in intrinsic permeation is caused by a nearby defect causing the
Ca degradation rather than the overall degradation of the ALD barrier film (note bottom left area of unaffected Ca)
Top Clear Encapsulation
Single Barrier
Substrate
High Barrier
Time
Moisture Barrier Permeation Measurement
CPI characterises the moisture permeation of clear barrier materials using the standard MOCON ‘Aquatran 1’ operating
at 38°C and 90% RH for large area measurement (50cm2), which is referred to as the extrinsic barrier permeation. For
intrinsic measurements, the Ca Test is used; this can measure the small area permeation and also highlight defects in the
barrier coating.
CPI, National Printable Electronics Centre, Thomas Wright Way, NETPark, Sedgefield, County Durham, TS21 3FG, UNITED KINGDOM
www.uk-cpi.com

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