Optical and Electro-Optic Properties Of Highly Oriented (Sr,Ba)Nb 2 O 6 Thin Films Prepared by Sol-Gel Process
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beam steering because of its large pyroelectric coefficient, excellent piezoelectric and electrooptic properties, and photorefractive sensitivity [1,21. Its figure of merit for photorefractive applications is more than 50 times higher than that of LiNbO 3 offering the possibility of much smaller device [3]. Also, the SBN is a ferroelectric solid solution between BaNb 20 6 and SrNb 20 6 with a tetragonal tungsten bronze (TTB) structure, and physical properties vary with its composition [2]. Recently, the demand for thin film processing has increased because of the development of integrated devices and low processing temperature. The SBN thin films, especially highly c-axis oriented SBN thin films, can be used for the integrated optical applications, such as electro-optic properties, photorefractive, and nonlinear optical applications [4,5]. Recently, Hirano and coworkers synthesized a highly c-axis oriented SBN (x = 0.5) film on an MgO(100) substrate by sol-gel method [6]. This sol-gel process has been developed for ferroelectric thin film fabrication due to excellent homogeneity, ease of chemical composition control, high purity, low processing temperature, and film uniformity over large area. 189 Mat. Res. Soc. Symp. Proc. Vol. 597 © 2000 Materials Research Society
In this work, highly oriented SBN thin films with various compositions on MgO(100) substrates were made by the sol-gel process. Optical and electrical properties such as optical propagation loss, refractive index, electro-optic effect and P-E hysteresis, of SBN thin films are characterized as a function of the film composition for optical waveguide applications. EXPERIMENT Three compositions were investigated in the present study with x = 0.25, 0.60 and 0.75. A precise procedure for preparing the precursor solution is shown in Fig. 1. The final solution, which has a concentration of 0.KM, is clear yellow without any suspended particles. The solution is able to be stored for several months due to using 2-methoxyethanol solvent. The mixed solution was spin-coated on substrates at 2000rpm for 30sec. After air drying for
5min,
the film was dried at 180'C for 10 min then 360°C for 10 min, to completely remove organic residues. A single coating yields about 600A film-thickness. This procedure was repeated until a desired thickness was obtained. These green films were heat-treated by a two-step heating process, to enhance the densification and the............................... Nb(OCH,), Ba metal crystallization of the films. In the two-step i sr metal heating process, the films were first heated from
2-Methoxycthanol 2-Methoxyethanol room temperature to 550"C with slow heating .......................... .'........................................................................ "...."d'.'..'d" rate (2°C /m in) and maintained at 550'C for 5h. .... Refluxing (12h) The temperature is then raised up to the Indried N2
crystallization temperature (900"C) with same heating rate. The effect of the two-step heating
process was described in another paper [7].
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