The influence of sputter-deposited indium tin oxide thin films on the strength of ultra-thin glass

Ultra-thin glass with a thickness of 100 µm or below is an attractive substrate for sputter deposition of thin films. However, research has shown that the deposition of functional coatings is often correlated with a significant strength reduction of the underlying glass. This study aims to identify relevant thin film properties that influence the ultra-thin glass strength using the example of indium tin oxide. For that, thin films with varying properties were sputter-deposited on ultra-thin glass. Then, correlations between glass strength and surface roughness, film morphology, and thin film stress were analyzed. It could be shown that the thin film stress and the film morphology are of major importance regarding the strength of the coated ultra-thin glass. In contrast, the surface roughness is expected to be of minor importance. Different models of the interaction between thin film and existing flaws in the glass are suggested to explain the experimental data. • Ultra-thin glass strength is reduced by sputtered nm-range indium tin oxide coatings. • Compressive thin film stress is considered to lead to a higher glass strength. • The roughness of the thin film is probably not correlated to the glass strength. • Surface bridging of existing cracks or flaws in the glass surface is likely. • A continuous stress transition zone between thin film and ultra-thin glass is assumed.