Integration of molecular-layer-deposited aluminum alkoxide interlayers into inorganic nanolaminate barriers for encapsulation of organic electronics with improved stress resistance

• Published in: Journal of vacuum science & technology. A, Vacuum, surfaces, and films Vacuum, surfaces, and films, 2015-01, Vol.33 (1)
• Main Authors: Hossbach, Christoph, Nehm, Frederik, Singh, Aarti, Klumbies, Hannes, Fischer, Dustin, Richter, Claudia, Schroeder, Uwe, Albert, Matthias, Müller-Meskamp, Lars, Leo, Karl, Mikolajick, Thomas, Bartha, Johann W.
• Format: Article
• Language: English
• Subjects: ALUMINIUM; ALUMINIUM OXIDES; CALCIUM; DEPOSITS; ENGINEERING; GLASS; LAYERS; MATERIALS SCIENCE; NANOSTRUCTURES; POLYMERS; SCANNING ELECTRON MICROSCOPY; STRESSES; SUBSTRATES; THIN FILMS; TITANIUM OXIDES; WATER VAPOR
• ISSN: 0734-2101; 1520-8559
• DOI: 10.1116/1.4901232

Diffusion barrier stacks for the encapsulation of organic electronics made from inorganic nanolaminates of Al2O3 and TiO2 with aluminum alkoxide interlayers have been deposited by atomic layer deposition (ALD) and molecular layer deposition (MLD). As a part of the MLD process development, the deposition of aluminum alkoxide with low a density of about 1.7 g/cm3 was verified. The ALD/MLD diffusion barrier stack is meant to be deposited either on a polymer film, creating a flexible barrier substrate, or on top of a device on glass, creating a thin-film encapsulation. In order to measure the water vapor transmission rate (WVTR) through the barrier, the device is replaced by a calcium layer acting as a water sensor in an electrical calcium test. For the barrier stack applied as thin-film encapsulation on glass substrates, high resolution scanning electron microscopy investigations indicate that the inorganic nanolaminates without MLD interlayers are brittle as they crack easily upon the stress induced by the corroding calcium below. The introduction of up to three MLD interlayers of 12 nm each into the 48 nm barrier film laminate successfully mitigates stress issues and prevents the barrier from cracking. Using the three MLD interlayer configurations on glass, WVTRs of as low as 10−5 g/m2/d are measured at 38 °C and 32% relative humidity. On polymer barrier substrates, the calcium is evaporated onto the barrier stack and encapsulated with a cavity glass. In this configuration, the corroding calcium has space for expansion and gas release without affecting the underlying barrier film. In consequence, a WVTR of about 3 × 10−3 g/m2/d is measured for all samples independently of the number of MLD interlayers. In conclusion, a stabilization and preservation of the ALD barrier film against mechanical stress is achieved by the introduction of MLD interlayers into the inorganic nanolaminate.