Mechanical behavior of ultrathin sputter deposited porous amorphous Al2O3 films

Abstract

The determination of the mechanical properties of porous amorphous Al 2 O 3 thin films is essential to address reliability issues in wear-resistant, optical and electronic coating applications. Testing the mechanical properties of Al 2 O 3 films thinner than 200 nm is challenging, and the link between the mechanical behavior and the microstructure of such films is largely unknown. Herein, we report on the elastic and viscoplastic mechanical properties of amorphous Al 2 O 3 thin films synthesized by reactive magnetron sputtering using a combination of internal stress, nanoindentation, and on-chip uniaxial tensile testing characterization, together with mechanical homogenization models to separate the effect of porosity from intrinsic variations of the response of the sound material. The porosity is made of voids with 2 to 30 nm diameter. The Young's modulus and hardness of the films decrease by a factor of two when the deposition pressure increases from 1.2 to 8 mTorr. The contribution of porosity was found to be small, and a change in the atomic structure of the amorphous Al 2 O 3 matrix is hypothesized to be the main contributing factor. The activation volume associated to the viscoplastic mechanism is around 100 . Differences in the atomic structure of the films could not be revealed by electron diffraction, pointing to a minute effect of atomic arrangement on the elastic properties.

Highly ductile amorphous oxide at room temperature and high strain rate

“…Experimental observations for Al2O3 at the nanoscale have been mixed: some measurements show prerequisites for plastic deformation at room temperature (15)(16)(17)(18), while others display fully brittle behavior (19)(20)(21).…”

A theory for coupled lithium insertion and viscoplastic flow in amorphous anode materials for Li-ion batteries

“…In particular, different sputtering pressures were used in the two sets of experiments. It has been previously reported that the sputtering pressure impacts the density, stiffness and strength of sputtered films (van der Rest et al, 2017;Kumari et al, 2018). It is therefore possible that it also affects the rate sensitivity, since rate sensitivity and strength are intrinsically coupled through the micro-mechanisms of plastic deformations in amorphous materials.…”

A Comparative Study of the Mechanical and Tribological Properties of Thin Al2O3 Coatings Fabricated by Atomic Layer Deposition and Radio Frequency Sputtering

“…The average hardness of both as-grown samples deposited by the two techniques is in agreement with the values reported in the literature for amorphous coatings, i.e., in the range from 5 to 12 GPa. [17,40,41,43,[45][46][47][48] Higher hardness values, in the range 8-20 GPa, are then usually found on transition alumina coatings. [17,18,40,41] Accordingly, both high temperature annealed coatings showed a higher hardness with respect to the corresponding unannealed films, as expected due to the transition from a totally amorphous alumina film to a crystalline structure containing the harder transition phases.…”