Critical tensile and compressive strains for cracking of Al2O3 films grown by atomic layer deposition

Abstract

Al2O3 atomic layer deposition (ALD) is a model ALD system and Al2O3 ALD films are excellent gas diffusion barrier on polymers. However, little is known about the response of Al2O3 ALD films to strain and the potential film cracking that would restrict the utility of gas diffusion barrier films. To understand the mechanical limitations of Al2O3 ALD films, the critical strains at which the Al2O3 ALD films will crack were determined for both tensile and compressive strains. The tensile strain measurements were obtained using a fluorescent tagging technique to image the cracks. The results showed that the critical tensile strain is higher for thinner thicknesses of the Al2O3 ALD film on heat-stabilized polyethylene naphthalate (HSPEN) substrates. A low critical tensile strain of 0.52% was measured for a film thickness of 80 nm. The critical tensile strain increased to 2.4% at a film thickness of 5 nm. In accordance with fracture mechanics modeling, the critical tensile strains and the saturation crack densities scaled as (1/h)1/2 where h is the Al2O3 ALD film thickness. The fracture toughness for cracking, KIC, of the Al2O3 ALD film was also determined to be KIC = 2.30 MPa m1/2. Thinner Al2O3 ALD film thicknesses also had higher critical strains for cracking from compressive strains. Field-emission scanning electron microscopy (FE-SEM) images revealed that Al2O3 ALD films with thicknesses of 30–50 nm on Teflon fluorinated ethylene propylene (FEP) substrates cracked at a critical compressive strain of ∼1.0%. The critical compressive strain increased to ∼2.0% at a film thickness of ∼20 nm. A comparison of the critical tensile strains on HSPEN substrates and critical compressive strains on Teflon FEP substrates revealed some similarities. The critical strain was ∼1.0% for film thicknesses of 30–50 nm for both tensile and compressive strains. The critical compressive strain then increased more rapidly than the critical tensile strain for thinner films with thicknesses < 30 nm. The high critical tensile and compressive strains for thin Al2O3 ALD films should be very useful for flexible gas diffusion barriers on polymers.

Opening-mode fractures of a brittle coating bonded to an elasto-plastic substrate

“…For the material properties of the alumina coating, it should be mentioned that it depends on the fabrication conditions. The material properties of the coating in this study were determined by considering the current anodization procedures and comparisons with existing studies in the literature (Wan et al, 2008;Gong et al, 2009;Jen et al, 2011;Accuratus, 2013).…”

“…12 illustrates the changing of the normalized applied tensile strain ðh 1 E f =2CÞ 1=2 e 0 with the crack-spacing/coatingthickness ratio (k=h 1 ), which represents the required external tensile load to form a new crack in the coating with a ratio of k=h 1 . The fracture toughness of the coating applied in this study is 3.5 MPa m 1=2 (Jen et al, 2011;Accuratus, 2013). Fig.…”

Enhanced Fracture Resistance of Flexible ZnO:Al Thin Films in Situ Sputtered on Bent Polymer Substrates

“…5, [8][9][10][11] In particular, thin films with thickness ≥100 nm have exhibited poorer structural integrity on polymer substrates when subjected to various mechanical stresses. 5, 8,9 For example, recently reported fracture energy and critical strain of ZnO:Al (~240 nm) thin films grown on flexible polymer substrates were 68.5 Jm -2 and 0.96 %, respectively.…”

Comparison of the cohesive and delamination fatigue properties of atomic-layer-deposited alumina and titania ultrathin protective coatings deposited at 200 °C

“…The critical energy release rate for ALD alumina was calculated to be G c,Al 2 O 3 = 29.3 ± 6.1 N m −1 [29], which is about six times more than the maximum G a,ch value in this study. No corresponding values for ALD titania could be found in the literature.…”