This article has been accepted for inclusion in a future issue of this journal. Content is final as presented, with the exception of pagination. IEEE TRANSACTIONS ON PLASMA SCIENCE 1 Preparation of Er 2 O 3 and TiO 2 Multilayer Films as Optical Filter Using Magnetron Sputtering Deposition Hiroharu Kawasaki, Yoshiaki Suda, Tamiko Ohshima, Yoshihito Yagyu, and Takeshi Ihara Abstract— Dispersion relations of refractive indexes and extinction coefficients of constituent materials were obtained by comparing the experimental and simulated transmission spectra of single-layer Er 2 O 3 and TiO 2 films. We designed multilayer thin films of [Er 2 O 3 /TiO 2 ] 6 /[Er 2 O 3 ] 2 /[TiO 2 /Er 2 O 3 ] 6 such that they can act as photonic crystals exhibiting a resonance wave- length of 514 nm. We prepared single-layer TiO 2 and Er 2 O 3 thin films on quartz glass substrates by employing a magnetron sputtering deposition method. Uniform films exhibiting very high transmittance values were obtained. Deposition rates of the TiO 2 and Er 2 O 3 films were 0.44 and 0.82 nm/s, respectively. [Er 2 O 3 /TiO 2 ] 6 /[Er 2 O 3 ] 2 /[TiO 2 /Er 2 O 3 ] 6 multilayer films, to be used for optical bandpass filter applications, were also prepared using a multitarget sputtering deposition method. Uniform and transparent films were obtained; however, the wavelength cor- responding to the highest transmittance was observed around 490 nm through ultraviolet-visible near-infrared spectroscopic measurements. The shift in the wavelength can be attributed to the low crystallinity and variations in the thicknesses of Er 2 O 3 and TiO 2 films. Index Terms— Multilayer thin films, plasma process, sputtering deposition. I. I NTRODUCTION M ULTILAYER thin films consisting of elements having different refractive indexes show optical bandpass prop- erty, implying that light with a specific wavelength can be transmitted or refracted. Such materials are widely used in industrial and environmental fields, such as in high-density- recording equipment and ecological houses [1]–[7]. TiO 2 is a unique material exhibiting versatile properties such as a high refractive index, wide bandgap, and good resis- tance to chemical and physical impacts. Therefore, it has been used for manufacturing various stratified media, antireflec- tion coatings, optical waveguides, and photonic crystal (PC) devices based on metal/ferroelectric/insulator/semiconductor Manuscript received March 28, 2016; revised May 20, 2016 and May 31, 2016; accepted June 1, 2016. This work was supported in part by the Grant-in-Aid for Scientific Research in Priority Areas (C) under Grant 23340181 and Grant 16K04999, in part by the Maekawa Houonkai Foundation, and in part by the Kato Foundation for Promotion of Science. H. Kawasaki, T. Ohshima, Y. Yagyu, and T. Ihara are with the National Institute of Technology, Sasebo College, Sasebo 857-1193, Japan (e-mail: h-kawasa@sasebo.ac.jp; ohshima@sasebo.ac.jp; yyagyu@sasebo.ac.jp; ihara@sasebo.ac.jp). Y. Suda is with the National Institute of Technology, Ishikawa College (e-mail: y-suda@ishikawa-nct.ac.jp). Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/TPS.2016.2575864 structures. Er has also attracted attention as a unique opti- cal material. For example, Er-doped fiber amplifiers domi- nate among commercial systems providing efficient gain in wavelength division-multiplexed signal transmission in both C (1530–1565 nm) and L (1565–1625 nm) bands. The refractive index of TiO 2 is 2.52 and that of Er 2 O 3 is 1.97. Therefore, multilayer [Er 2 O 3 /TiO 2 ] m thin films might act as optical bandpass filters [8]–[11]. Grishin et al. prepared high- performance [Er 2 O 3 /TiO 2 ] m PC films using a pulsed laser deposition (PLD) method at 200 °C and controlled the resonant wavelength at 514, 524, and 540 nm. Transmission spectra of the obtained PCs were found be in good agreement with those predicted theoretically based on 2 × 2 transfer matrix formalism and complex refractive index parameters obtained using the calibration procedure performed for the reference films of constituent materials. However, as the deposition area of the film was small, PLD was employed in the synthesis. We prepared functional thin films under various deposition conditions using the sputtering deposition method with tungsten carbide, silicon carbide, chromium carbide, titanium carbide, cubic boron nitride, carbon nitride, and silicon nitride [12]–[16]. All these samples exhibited high quality, including high crystallinity and hardness. Especially, TiO 2 films were prepared as photocatalyst, hydrophilic, and heat-mirror thin films, with deposition area larger than several centimeters square. This paper reports the preparation of large-area multilayer [Er 2 O 3 /TiO 2 ] m thin films using multitarget magnetron sputter- ing methods. We first provide details on the design of multi- layered [Er 2 O 3 /TiO 2 ] m bandpass films. The preparation of thin films by sputtering deposition and the analyses of these films by field emission scanning electron microscopy (FESEM), atomic force microscopy (AFM), X-ray diffraction (XRD), and ultraviolet-visible near-infrared (UV-Vis-NIR) spectroscopy are discussed. II. EXPERIMENT Schematic of the experimental apparatus is shown in Fig. 1. The deposition chamber was made of stainless steel with a diameter of 400 mm and a height of 450 mm. First, metal-oxide targets were set up on stainless-steel target holders. Bulk TiO 2 (99.95%) target and Er 2 O 3 (99.95%) having a diameter of 30 mm were used. The chamber was 0093-3813 © 2016 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission. See http://www.ieee.org/publications_standards/publications/rights/index.html for more information.