Amorphous aluminum oxide is a promising engineering ceramic material in modern electronics industry with potential applications in optoelectronics, semiconductors, flexible electronic systems etc. This oxide system is generally considered to be brittle in nature due to the lack of deformation mechanisms. The inherent brittleness of oxides limits their use in many advanced technologies that rely more on damage tolerant materials to improve the device efficiency and life cycle. However, recent studies reported that nanoscale thin films of amorphous aluminum oxide, made by pulsed laser deposition, exhibit significant unconfined plasticity at room temperature under all principal loading modes. They proposed that the observed viscous creep plasticity could, in principle, be extended to micrometer length scales and beyond, if the material can be fabricated in fully dense and flaw-free form.

In this study, we investigate further insights to the plasticity and fracture behavior of amorphous aluminum oxide thin films fabricated by different deposition techniques, at micrometer length scales. Amorphous aluminum oxide thin films were fabricated with different thin film deposition routes – sputtering, pulsed laser deposition and atomic layer deposition. Micropillar compression of these films depicted substantial plasticity in the material whereby the pillars could be compressed to 50% total strain, without fracture, over large range of strain rates (10^-3-10³ s^-1). It was observed that pulsed laser deposited thin film showed tensile plastic behavior upon bending which finds potential use in flexible electronics. Elastic brittle fracture was observed from the notched microcantilever fracture tests with similar fracture toughness values in all films, suggesting that the presence of a flaw triggers the inherent brittle nature of ceramics in these systems. In particular, the experimental interpretations of the operative deformation mechanism(s) based on activation parameters for deformation (activation volumes, apparent activation energies) are compared with the bond breakage/swapping observations from atomistic simulations. Finally, the deformation behavior of amorphous alumina contrasted with other similar amorphous oxide systems and future research directions will be discussed. This study provides the possibility to enhance the plasticity in amorphous materials to become more damage tolerant and widens their range of applications.