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MATERIALS RESEARCH

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Electrical characterization of BaTiO3 heteroepitaxial thin films by hydrothermal synthesis A.T. Chien,a) X. Xu, J.H. Kim,b) J. Sachleben,c) J.S. Speck, and F.F. Lange Materials Department and Materials Research Laboratory, University of California, Santa Barbara, CA 93106 (Received 9 November 1998; accepted 27 April 1999)

The electrical properties of hydrothermally grown epitaxial pseudocubic BaTiO3 thin films formed on epitaxial electrode layers of SrRuO3 on SrTiO3 single crystal substrates have been evaluated by variable frequency dielectric testing. The initial as-synthesized BaTiO3 film displayed a dielectric constant of 450 with very high losses (tan ␦ ∼ 100%) at 10 kHz due to OH− and H2O, incorporated during growth, contributing to migration losses within the film. Improvements were seen with increasing postprocessing heat-treatment time and temperature with improved properties seen after a heat treatment at 300 °C for 24 h (␧ ∼ 200, tan ␦ ∼ 8%). Relationships were established for dielectric constant and loss tangent with structural changes observed by Fourier transform infrared spectroscopy, thermal gravimetric analysis, nuclear magnetic resonance spectroscopy, and x-ray diffraction.

I. INTRODUCTION

Barium titanate (BaTiO3) is extensively used in the electronics industry because of its high dielectric constant and ferroelectric properties.1 For dielectric applications, dielectric constant (␧r), loss tangent (tan ␦), breakdown voltage (VB), and leakage current (JL) are considered to be important physical properties. Consequently, when selecting and processing materials, high ␧r and VB and low tan ␦ and JL are often desired where almost all applications benefit from high dielectric constant and breakdown voltage and low loss tangent and leakage current. Bulk and thin-film BaTiO3 is traditionally made by conventional solid-state or vapor-phase methods (e.g., pulsed-laser deposition, metalorganic chemical vapor deposition, and sputtering), which often involve either high processing temperatures or high vacuum environments. Our interest is in using direct solution synthesis routes to grow epitaxial thin films at low temperatures.2 Hydrothermal epitaxy is a technique that utilizes aqueous chemical reactions to synthesize inorganic materials

a)

Present address: Chemistry and Materials Science, Lawrence Livermore National Laboratory, L-370, Livermore, California 94551. b) Present address: Department of Ceramic Engineering, Chonnam National University, 300 Yongbong-Dong, Puk-Gu, Kwangju 500-757, Korea. c) Present address: Solid-State NMR Facility, Campus Chemical Instrument Center, The Ohio State University, Johnston Laboratory 119, 176 West 18th Avenue, Columbus, Ohio 43210. 3330

http://journals.cambridge.org

J. Mater. Res., Vol. 14, No. 8, Aug 1999 Downloaded: 06 Apr 2015

in the form of epitaxial thin films on structurally similar single-crystal substrates. Film growth occurs at significantly lower temperatures than vapor methods, which effectively eliminates the