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Proceedings Paper

Temperature-induced changes in optical properties of thin film TiO2-Al2O3 bi-layer structures grown by atomic layer deposition
Author(s): Rizwan Ali; Muhammad Rizwan Saleem; Seppo Honkanen
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Paper 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.

Paper Details

Date Published: 7 March 2016
PDF: 8 pages
Proc. SPIE 9749, Oxide-based Materials and Devices VII, 97490O (7 March 2016); doi: 10.1117/12.2212249
Show Author Affiliations
Rizwan Ali, Univ. of Eastern Finland (Finland)
Muhammad Rizwan Saleem, Univ. of Eastern Finland (Finland)
National Univ. of Sciences and Technology (Pakistan)
Seppo Honkanen, Univ. of Eastern Finland (Finland)


Published in SPIE Proceedings Vol. 9749:
Oxide-based Materials and Devices VII
Ferechteh H. Teherani; David C. Look; David J. Rogers, Editor(s)

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