Abstract
Mechanical fracture properties were studied for the common atomic-layer-deposited Al2O3, ZnO, TiO2, ZrO2, and Y2O3 thin films, and selected multilayer combinations via uniaxial tensile testing and Weibull statistics. The crack onset strains and interfacial shear strains were studied, and for crack onset strain, TiO2/Al2O3 and ZrO2/Al2O3 bilayer films exhibited the highest values. The films adhered well to the polyimide carrier substrates, as delamination of the films was not observed. For Al2O3 films, higher deposition temperatures resulted in higher crack onset strain and cohesive strain values, which was explained by the temperature dependence of the residual strain. Doping Y2O3 with Al or nanolaminating it with Al2O3 enabled control over the crystal size of Y2O3, and provided us with means for improving the mechanical properties of the Y2O3 films. Tensile fracture toughness and fracture energy are reported for Al2O3 films grown at 135 °C, 155 °C, and 220 °C. We present thin-film engineering via multilayering and residual-strain control in order to tailor the mechanical properties of thin-film systems for applications requiring mechanical stretchability and flexibility.
Highlights
Atomic layer deposition (ALD) is a thin-film deposition technique for the fabrication of conformal coatings with sub-nanometer-scale thickness control
The distinct diffraction maxima seen in the grazing incidence X-ray diffraction (GIXRD) patterns for the ZnO, Y2O3, Y2O3 on Al2O3, and ZrO2 on Al2O3 samples indicate polycrystalline structures for these thin films (Figure 2)
The GIXRD patterns for the Y2O3/Al2O3 nanolaminate and Al-doped Y2O3 were characteristic for 3(n.2eFarralyg)maemntaotriponhoofutshemFailtmersials; the low-intensity broad features seen at around 32◦tmiveiglyhtsiimndiliacraftoertahlel tphreessaemncpeleosfsvtuerdyiesdminaltlhnisanwoocrrky.sAtasls
Summary
Atomic layer deposition (ALD) is a thin-film deposition technique for the fabrication of conformal coatings with sub-nanometer-scale thickness control. A wide range of industrially relevant metal oxides and other materials can be deposited with ALD for many applications in the fields of microelectronics, energy generation and storage, and protective coatings. Much of the research on ALD has focused on the surface chemistry of the ALD processes and on the growth and film characteristics on a wide variety of surfaces. Regardless of the strong growth of the ALD field, the mechanical properties of the ALD-fabricated thin films have received relatively little attention. Mechanical robustness of coating materials is desired for applications where the materials are subjected to straining. This is the case for coatings on flexible substrates, or coatings on materials that exhibit significant volumetric changes (e.g., owing to large changes in temperature). The mechanical robustness alone is not enough for high-performance materials, but the desired mechanical properties must be considered alongside the other properties of that material
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