THE STUDY OF MOISTURE PERMEATION BARRIER CHARACTERISTICS OF Al2O3 THIN FILM DEPOSITED BY SPATIAL ATOMIC LAYER DEPOSITION

Abstract

Organic light emitting diodes (OLED) have recently emerged as a next generation display. OLED are highly acclaimed because of their vivid color, wide size and thinness, which are due to the self-emitting properties of organic materials used in their fabrication. However, the barrier property required for OLEDs is less than 1.0 × 10-5 g/m2-day, because water and oxygen vapor can deteriorate the OLEDs performance in many ways, one of which is that water vapor can oxidize metallic cathode, which reduces the electron injection in OLED device. One of the most common techniques is to use glass for encapsulation of OLED. However, such a technique is not applicable for flexible devices due to its brittle behavior of glass under mechanical stress. Therefore, thin film encapsulation (TFE) has been researched to replace glass with flexible display. Single inorganic moisture barrier layers, which are approximately 10 - 100 nm in thickness, are fabricated by various physical and chemical techniques such as sputtering, thermal evaporation, plasma enhanced chemical vapor deposition (PECVD) and atomic layer deposition (ALD). Among these deposition methods, ALD is a thin film growth method allowing low temperature growth, better step coverage, excellent large area uniformity, precise thickness control, and pinhole-free thin films needed for superior permeation barriers. However, one of the main drawbacks inherent to typical time-divided ALD is the relatively low throughput of such ALD system due to the long cycle time, which can be about 10 seconds or more at low temperatures. Recently, there have been many developments in space-divided ALD, enabling ALD with high growth rates and high throughput. In spatial ALD, the reactants are continuous injected while moving the substrate or coating head. And these gases are isolated in different location within the system through the use of purge and pumping modules ALD cycles are not performed in the time domain but in the spatial domain. The precursor and reactant are continuously injected in different spaces using distinct reaction zones separated by purge zones. Spatial ALD combines the advantages of conventional ALD (such as defect-free films and uniform deposition over a large area) and adds the advantage of high growth rate. For this reason, spatial ALD has been proposed as an innovative technique for the growth of thin films in the electronics and solar cell industries In this study, we investigated the moisture permeation barrier characteristic of Al2O3 thin films deposited using fast spatial ALD at low temperatures (< 100 °C) onto an industrially relevant substrate of 2G glass (370 × 470 mm2). We successfully reduced a single ALD cycle to less than 1 second at an 800 mm/sec scan speed, resulting in a high growth rate (70 Å/min) that is 5 to 10 times faster than the conventional time of divided ALD (~ 6 Å/min) at low temperatures. In addition, we investigated the physical and chemical properties of the deposited Al2O3 films using spectroscopic ellipsometry, FESEM, AES, and XRR. UV-vis was also used to measure the optical properties. Finally, the moisture barrier performance of the deposited film was characterized using MOCON test and luminance lifetime tests after deposition of Al2O3 on OLED panel.