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Barrier Films for Flexible Electronics

Brand new December 2008

Needs, Players & Opportunities

By Dr Harry Zervos

For those developing flexible electronics, seeking materials needs and opportunities, this is a must

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Description

The biggest opportunity for OLED displays and organic photovoltaics is when these devices can be flexible, allowing them to be more robust, versatile and made in large areas compared to conventional displays and photovoltaics. However, many of the materials used in OLED displays and organic photovoltaics are sensitive to the environment, limiting their lifetime. These materials can be protected using substrates and barriers such as glass and metal, but this results in a rigid device and does not satisfy the applications demanding flexible devices. Plastic substrates and transparent flexible encapsulation barriers can be used, but these offer little protection to oxygen and water, resulting in the devices rapidly degrading.

In order to achieve device lifetimes of tens of thousands of hours, water vapor transmission rates (WVTR) must be 10-6 g/m2/day, and oxygen transmission rates (OTR) must be < 10-3 cm3/m2/day. For Organic Photovoltaics, the required WVTR is not as stringent as OLEDs require but is still very high at a level of 10-5 g/m2/day. These transmission rates are several orders of magnitude smaller than what is possible using any plastic substrate, and they can also be several orders of magnitude smaller than what can be measured using common equipment (MOCON) designed for this purpose (Table 1). For these (and other) reasons, there has been intense interest in developing transparent barrier materials with much lower permeabilities.

This concise and unique report from IDTechEx gives an in-depth review to the needs, emerging solutions and players. It addresses specific topics such as:

Companies which are active in the development of high barrier films and their achievements on the field to date.
Surface smoothness and defects (such as cracks and pinholes) and the effect that these characteristics would have on the barrier behavior of the materials studied.
Traditional methods of measurement of permeability are reaching the end of their abilities. The MOCON WVTR measurement device, which has been an industry standard, cannot give adequate measurements at the low levels of permeability required for Organic Photovoltaics and OLEDs. Other methods of measurement and equipment developed are being discussed.
Forecasts for OLEDs and OPV, in order to understand the influence that the development of flexible barriers would have at the mass deployment and adoption of these technologies.

For those developing flexible electronics, seeking materials needs and opportunities, this is a must-read report.

Table of Contents

1.	SCOPE
2.	INTRODUCTION TO ENCAPSULATION
3.	SURFACE SMOOTHNESS - DEFECTS
3.1.	Important considerations of surface smoothness
3.2.	Micro Defects
3.2.2.	Pinholes
3.2.3.	Smoothness / Cracks-Scratches
3.2.4.	Nanodefects
4.	COMPANIES
4.1.	Vitex
4.2.	GE
4.3.	3M
4.4.	CPI
4.5.	Others
4.6.	Best performing barriers developed to date
5.	BARRIER MEASUREMENTS
5.1.	The Calcium test
5.2.	MOCON
5.3.	Black Spot Analysis
5.4.	Tritium Test
5.5.	CEA
5.6.	3M
5.7.	IMRE
5.8.	Standardization efforts
6.	OLED - ORGANIC PV FORECASTS
7.	CONCLUSIONS
8.	REFERENCES
	APPENDIX 1: ATOMIC LAYER DEPOSITION
	APPENDIX 2: GLOSSARY
	APPENDIX 3: IDTECHEX PUBLICATIONS
	TABLES
2.1.	Water vapor and oxygen transmission rates of various materials.
2.2.	Requirements of barrier materials
3.2.	Oxygen transmission rates of polypropylene with various coatings.4, 7
4.1.	Overview of promising high barrier technologies
5.1.	Metrics and standards for organic solar cell components42
6.1.	OLED forecasts for display, billboard & signage and lighting applications
6.2.	OLED forecasts for non-rigid display, billboard & signage and lighting applications
6.3.	Percentage of the thin film market share represented by OPV
	FIGURES
1.1.	Examples of flexible OLED displays by SONY and AddVision
1.2.	Flexible OLED fabricated using IMRE's high barrier substrate and encapsulation technique44
1.3.	Flexible Solar Cell developed by Fraunhofer IPMS
2.1.	Schematic diagrams for encapsulated structures a) conventional b) laminated c) deposited in situ4
2.2.	Scanning electron micrograph image of a barrier film cross section6
3.1.	Visual defects of a selection of materials with barrier films highlighted through calcium corrosion test. Optical microscope magnification 10x.44
3.2.	SEM pictures of the Atmospheric Plasma Glow Discharge deposited silica-like films on polymer substrates. Left: Film with embedded dust particles . Right: uniform film27
3.3.	OTR as a function of defect density for Al(o), SiOx (٭), and SiNx (■) films. The correlation between defect density and the oxygen transmission rate shown was attributed to pinhole defects4
3.4.	SEM image of a pinhole defect formed from a dust particle32
3.5.	Scanning electron microscope image of ITO coated on parylene/polymer film34
3.6.	The measurement of OLED's lifetime of SiON/PC/ITO and SiON/parylene/PC/parylene/ITO substrate34
4.1.	Examples of polymer multi-layer (PML) surface planarization a) OLED cathode separator structure b) high aspect ratio test structure.3, 8
4.2.	Vitex multilayer deposition process8.
4.3.	SEM cross section of Vitex Barix material with four dyads.
4.4.	Optical transmission of Vitex Barix coating8.
4.5.	Edge seal barrier formation by deposition through shadow masks10.
4.6.	Three dimensional barrier structure. Polymer is shown in red, and oxide (barrier) shown in blue10.
4.7.	Schematic of flexible OLED with hybrid encapsulation31
4.8.	Schematic of cross section of graded barrier coating and complete barrier film structure1.
4.9.	DuPont Displays technology pipeline
4.10.	Specifications on WVTR for different applications, as seen by Vitex Systems36
4.11.	3M specifications on WVTR and OTR for high barrier applications with stringent requirements 14
5.1.	2.25 mm2 area of a 50 nm layer of Ca deposited onto barrier coated PET viewed through the substrate. i. Image after 1632 h of exposure to atmosphere; ii. Image analysis whereby the gray scale of Ca degradation is processed to yield a two-color image with
5.2.	MOCON's Aquatran™ Model 138
5.3.	MOCON's Aquatran™ schematic38
5.4.	MOCON's OX-TRAN® Model 2/1039
5.5.	Silica induced black spots, letters A & B mark black spots with a centralized black dot (silica particle)32
5.6.	Black spot formation and growth mechanisms 32
5.7.	General Atomics HTO WVTR testing apparatus40
6.1.	Stages of reliability R&D, current status of OPV41
7.1.	The iRex iLiad and the Amazon Kindle rigid e-book readers
7.2.	PVI's flexible electrophoretic display and color electrophoretic display by SAMSUNG LCD, demonstrated at SID 2008