Optical properties and hardness of highly a-axis oriented AlN films

TL;DR

This study investigates the optical and nanomechanical properties of highly a-axis oriented AlN thin films, revealing their potential for protective coatings and piezoelectric applications due to their superior hardness and elastic modulus.

Contribution

First detailed characterization of highly a-axis oriented AlN films' optical and mechanical properties using reactive DC magnetron sputtering.

Findings

Refractive index of 1.93 at 546 nm

Hardness of 17 GPa

Elastic modulus of 190 GPa

Abstract

This paper reports optical and nanomechanical properties of seldom studied highly a-axis oriented AlN thin films for the first time. These films were deposited by reactive DC magnetron sputtering technique at an optimal target to substrate distance of 180 mm. Bragg-Brentano geometry X-ray and rocking curve (FWHM = 52 arcsec) studies confirmed the preferred orientation. Spectroscopic ellipsometry revealed that these films exhibit a refractive index of 1.93 at a wavelength of 546 nm. The hardness and elastic modulus of these films were 17 GPa and 190 GPa, respectively. The mechanical properties obtained here are much higher than the earlier reported and therefore can be useful as protective coating in thermo printing devices, piezoelectric films in bulk acoustic wave resonators.