Deposition and characterization of crystalline conductive RuO 2 thin films
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Deposition and characterization of crystalline conductive R11O2 thin films Q.X. Jia, S.G. Song,a) S.R. Foltyn, and X.D. Wu Materials Science and Technology Division, Superconductivity Technology Center, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (Received 30 May 1995; accepted 5 July 1995)
Highly conductive metal-oxide RuO 2 thin films have been successfully grown on yttria-stabilized zirconia (YSZ) substrates by pulsed laser deposition. Epitaxial growth of RuO 2 thin films on YSZ and the atomically sharp interface between the RuO 2 and the YSZ substrate are clearly evident from cross-sectional transmission electron microscopy. A diagonal-type epitaxy of RuO 2 on YSZ is confirmed from x-ray diffraction measurements. The crystalline RuO 2 thin films, deposited at temperatures in the range of 500 °C to 700 °C, have a room-temperature resistivity of 35 ± 2/ttfi-cm, and the residual resistance ratio (R300 K/RA.I K) is around 5 for the crystalline RuO 2 thin films.
There is currently considerable interest in transition metal-oxides with rutile structure since they present a very attractive metallization option in a variety of applications. One of the most promising conductive metal-oxides is ruthenium oxide (RuO 2 , a = b = 0.44902 n m , c = 0.31059 nm). Experimental results have demonstrated that RuO2 thin films can be used as a good diffusion barrier in silicon contact metallization with Al overlayers,1"3 as a conductor in interconnections,4 and as a precision thin film resistor in hybrid circuits.5 The good thermal stability, low resistivity, and excellent diffusion barrier properties of RuO2 also make it very attractive as a bottom electrode for high dielectric constant or ferroelectric thin film capacitors. Experimental results have shown that the use of RuO 2 as an electrode instead of Pt for PbZr x Tii_ x O 3 thin film capacitors can avoid polarization fatigue of the capacitors.6"8 Improved device performance has also been demonstrated for the high dielectric constant thin film capacitors by using RuO 2 as a bottom electrode.9"1' Polycrystalline RuO 2 thin films have been routinely deposited on different substrates by either sputtering, 23,6,7 or metal-organic chemical vapor deposition. 112 The residual resistance ratio (RRR), defined as RRR = R300 K/R4.2 K, 13 of the polycrystalline RuO2 thin films is in the range of 1-2, 314 compared with a value of 20-800 for bulk single-crystal RuO 2 . 15
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Present address: MST-5, Los Alamos National Laboratory, Los Alamos, New Mexico 87545. J. Mater. Res., Vol. 10, No. 10, Oct 1995 http://journals.cambridge.org
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The room-temperature resistivity, which is one of the most important parameters for applications of RuO 2 thin film as an electrode material, is in the range of 100 /mil-cm for most of the polycrystalline RuO 2 thin films. This value is three times higher than the 35 ^fl-cm of the bulk single-crystal RuO 2 . 15 In this paper, we, for the first time, report epitaxial growth of RuO 2 thin films with electrical properties
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