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Characterization of Conductive RuO2 Thin Film as Bottom electrodes for Ferroelectric Thin Films. S. Bhaskar, P. S. Dobal, S. B. Majumder and R. S. Katiyar Department of Physics, University of Puerto Rico, Rio Piedras campus, San Juan, PR 00931. ABSTRACT Ruthenium Oxide (RuO2) thin films were prepared on silicon substrates by solution chemistry technique. X-ray Diffraction (XRD), Atomic Force Microscopy (AFM), microRaman, X-ray photoelectron spectroscopy (XPS), and four probe Van-der-paw technique were used for the film characterization. X-ray analysis shows a rutile structure in these films. The films annealed at 700oC showed lowest resistivity of 29 x 10-5 ohm-cm. The presence of Eg, A1g, and B2g modes is consistent with the Raman spectrum of rutile phase. These modes as well as additional unidentified band at about 477 cm-1 were investigated by temperature dependent Raman studies. Based on the result, band at 477 cm-1 that disappears above 370 K is attributed to hydrated RuO2 present in the films. XPS analysis show stoichiometric rutile RuO2 present in the films. Small concentrations of RuCl3, RuO3 and hydrated RuO2 were also detected. Pb0.9La0.15TiO3 (PLT15) thin films were deposited on RuO2/Si substrates and characterized for its ferroelectric properties to demonstrate that solution deposition technique offers an alternative approach for preparing high quality RuO2 bottom electrodes. INTRODUCTION

Oxide electrodes, such as ruthenium oxide (RuO2), lanthanum strontium cobalt oxide (LSCO), strontium ruthenate (SrRuO3), and yittrium barium copper oxide (YBCO) are attractive candidates to be used as bottom electrodes for ferroelectric memory devices [1]. Among these, RuO2 with tetragonal rutile structure exhibits various interesting properties such as lower bulk resistivity (∼40 µΩm), good thermal stability, and diffusion barrier capability [2]. These properties make RuO2 a good candidate material for bottom electrodes in high dielectric constant and ferroelectric thin film capacitors. Deposition techniques like rf-sputtering [3], pulsed laser deposition [4] and chemical vapor deposition [5] have been widely used to synthesize RuO2 thin films. Few reports are available on growth of RuO2 thin films by solution chemistry technique and on surface characterization by XPS and micro Raman spectroscopy. In this paper we report the synthesis of RuO2 thin films on silicon substrates using the solution chemistry technique. The surface and structural characterization of these films were done by XPS, XRD, and micro-Raman spectroscopy. Of central interest is the evaluation of the quality of RuO2 thin films in terms of their structure, composition, stoichiometry, and electrical conductivity for oxide bottom electrodes in ferroelectric thin films. EXPERIMENTAL

RuCl3.x.H2O was used as a precursor material was dissolved in absolute alcohol and diluted to 0.05M/L for coating. The precursor solution was spun coated on the silicon substrates CC4.7.1

at 3000 rpm for 20s. The films were annealed in the temperature range 300oC – 700oC f