Thick uniform epsilon-near-zero ITO films grown by hi-power impulse magnetron sputtering

Abstract

We report on the growth and characterization of wavelength-thick indium tin oxide (ITO) films deposited using high power impulse magnetron sputtering (HiPIMS) with post deposition processing to achieve an epsilon near zero (ENZ) property at 1550 nm telecom wavelengths. The goal is to fabricate 1550 nm ENZ films for use as claddings for waveguides, resonators, or high-contrast metastructures in photonic devices operated at telecom wavelengths. We developed a HiPIMS growth and post-annealing process to improve on existing ENZ ITO quality and uniformity. By consecutively annealing the ITO film, the plasma frequency gradually shifts, enabling fine tuning of the ENZ wavelength regime from 1800 to 1500 nm. The films were characterized using spectroscopic ellipsometry, transmission electron microscopy, x-ray diffraction, and energy dispersive x-ray spectroscopy. Our micro-analyses shows that the change in the microstructure resulted in the change in the optical properties of the ITO. These findings allow us to control the ENZ property at the desired wavelength and reduce the absorption loss, which is beneficial for device application.