Enhancing cover glass fracture resistance for hand-held devices with PEALD-based Al2O3 coating

Abstract Chemically strengthened glass (also known as ion exchanged glass) is widely used for hand-held devices due to excellent mechanical strength. However, only top and bottom planar surfaces are sufficiently protected following a series of machining processes such as drilling, cutting and milling for manufacturing and assembly. Micro cracks that remain on the machined surface of the glass edges become very vulnerable to shock impact loading. In this study we suggest a novel PEALD technique to encapsulate surface defects with a 100 nm thickness layer of high-strength ceramics such as Al 2 O 3 . In order to optimize PEALD parameters, we have examined best practices for testing chemically strengthened cover glasses. By conducting both Charpy impact test and 3-point bending test, it was found that impact resistance and flexural toughness of the PEALD-coated cover glass were 35%–40% and 21% higher compared to non-coated samples. Through the analysis of the state and elements of the machined surface with Al 2 O 3 (500 nm) coating it was verified that the coated layer uniformly covers the entire surface of the glass and fully infiltrates into the micro cracks. This study confirms that Al 2 O 3 ceramic coated with PEALD improves not only overall glass strength, but also overcomes the shortcomings of chemically strengthened glass machining.