Saturday, November 8, 2014

Stabilization of ALD barrier film by MLD interlayers by TU Dresden

Christoph Hossbach, Frederik Nehm, Aarti Singh, Hannes Klumbies, Dustin Fischer, Claudia Richter, Uwe Schroeder, Matthias Albert, Lars Müller-Meskamp, Karl Leo, Thomas Mikolajick and Johann W. Bartha

J. Vac. Sci. Technol. A 33, 01A119 (2015);

Diffusion barrier stacks for the encapsulation of organic electronics made from inorganic nanolaminates of Al 2O3 and TiO2 with aluminum alkoxide interlayers have been deposited byatomic 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/cm3was 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-filmencapsulation. 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 electricalcalcium 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 10−5g/m2/d are measured at 38 °C and 32% relative humidity. On polymer barrier substrates, thecalcium 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.

Schematic drawing of a Ca test built on an ALD barrier coated foil substrate (barrier film test configuration)

Top view of glass Ca tests coated with ALD/MLD barrier stacks consisting of a 48 nm Al-O/Ti-O nanolaminate with zero to three aluminum alkoxide interlayers of 12 nm thickness. The layers were deposited at 90 °C on Ca tests on glass and aged at 38 °C and 32% r.h.—picture taken with high resolution scanning electron microscopy after aging.