Temperature-induced changes in optical properties of thin film TiO2-Al2O3 bi-layer structures grown by atomic layer deposition

Rizwan Ali; Muhammad Rizwan Saleem; Seppo Honkanen

doi:10.1117/12.2212249

7 March 2016 Temperature-induced changes in optical properties of thin film TiO₂-Al₂O₃ bi-layer structures grown by atomic layer deposition

Rizwan Ali, Muhammad Rizwan Saleem, Seppo Honkanen

Author Affiliations +

Proceedings Volume 9749, Oxide-based Materials and Devices VII; 97490O (2016) https://doi.org/10.1117/12.2212249
Event: SPIE OPTO, 2016, San Francisco, California, United States

Abstract

We investigate the optical properties and corresponding temperature-induced changes in highly uniform thin amorphous films and their bi-layer stacks grown by Atomic Layer Deposition (ALD). The environmentally driven conditions such as temperature, humidity and pressure have a significant influence on optical properties of homogeneous and heterogeneous bi-layer stacked structures of TiO₂–Al₂O₃ and subsequently affect the specific sensitive nature of optical signals from nano-optical devices. Owing to the super hydrophilic behavior and inhibited surface defects in the form of hydrogenated species, the thermo-optic coefficient (TOC) of ~ 100 nm thick ALD–TiO₂ films vary significantly with temperature, which can be used for sensing applications. On the other hand, the TOC of ~ 100 nm thick ALD–Al₂O₃ amorphous films show a differing behavior with temperature. In this work, we report on reduction of surface defects in ALD–TiO₂ films by depositing a number of ultra-thin ALD–Al₂O₃ films to act as impermeable barrier layers. The designed and fabricated heterostructures of ALD–TiO₂/Al₂O₃ films with varying ALD–Al₂O₃ thicknesses are exploited to stabilize the central resonance peak of Resonant Waveguide Gratings (RWGs) in thermal environments. The temperature-dependent optical constants of ALD–TiO₂/Al₂O₃ bi-layer films are measured by a variable angle spectroscopic ellipsometer (VASE), covering a wide spectral range 380 ≤ λ ≤ 1800 nm at a temperature range from 25 to 105 °C. The Cauchy model is used to design and retrieve refractive indices at these temperatures, measured with three angles of incidence (59°, 67°, and 75°). The optical constants of 100 nm thick ALD–TiO₂ and various combinational thicknesses of ALD–Al₂O₃ films are used to predict TOCs using a polynomial fitting algorithm.

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Rizwan Ali, Muhammad Rizwan Saleem, and Seppo Honkanen "Temperature-induced changes in optical properties of thin film TiO₂-Al₂O₃ bi-layer structures grown by atomic layer deposition", Proc. SPIE 9749, Oxide-based Materials and Devices VII, 97490O (7 March 2016); https://doi.org/10.1117/12.2212249

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KEYWORDS

Atomic layer deposition

Thin films

Titanium dioxide

Refractive index

Thermal optics

Temperature metrology

Optical properties

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