BaRuO 3 thin film electrode for ferroelectric lead zirconate titanate capacitors
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BaRuO3 thin film electrode for ferroelectric lead zirconate titanate capacitors Sang-Mo Koo, Li-Rong Zheng, and K.V. Raoa) Department of Condensed Matter Physics, Royal Institute of Technology, S-100 44, Stockholm, Sweden (Received 30 January 1999; accepted 5 June 1999)
The characteristics of a ferroelectric Pb(Zr0.52Ti0.48)O3 (PZT) capacitor on conductive BaRuO3 thin films deposited by pulsed laser deposition (PLD) were investigated. The BaRuO3 layer grown epitaxially on LaAlO3(100) substrates at a substrate temperature of 700 °C was found to have a resistivity around 145 ⍀ cm at 300 K. The subsequently deposited PZT film showed a c-axis orientation perpendicular to the substrate, and the remnant polarization, ⌬P (⳱ P* − Pˆ), and coercive field, EC, of the capacitor were 24.7 C/cm2 and 52 kV/cm, respectively. Fatigue characteristics of the PZT on BaRuO3 electrodes are far better than those obtained with polycrystalline PZT with Pt structures and comparable to those on epitaxial YBa2Cu3O7−x electrodes. With the new metallic electrode, the PZT layer exhibits no serious degradation in fatigue endurance up to 1010 cycles.
There have been extensive studies of ferroelectric thin films for many applications, such as optical waveguides,1 ferroelectric random-access memories (FRAMS), dynamic random-access memories (DRAM),2,3 etc. Among various kinds of ferroelectric materials, the lead zirconate titanates (PZT) are the most investigated because of their relatively high remnant polarization, high dielectric constant, low operating voltage, and low leakage current. Conventionally, PZT thin films were grown on Pt-based electrodes with additional Pt top electrodes to form the capacitor structure of which the electrical properties have been extensively studied.4,5 However, the PZT films with Pt electrodes suffer from a serious loss of switchable polarization, which is one of the major hindrances to device applications. Recently, metallic oxides such as RuO2, YBa2Cu3O7−x (YBCO), La0.5Sr0.5CoO3 (LSCO), and LaNiO3 (LNO) with good electrical conductivity have drawn great attention, since they can improve the fatigue performance of PZT thin films.6 –9 Many studies on the growth of PZT/ SrRuO3 heterostructures and characterization of their ferroelectric properties have been published.10 –12 However, to the best of our knowledge, there is no report on PZT/ BaRuO3 heterostructures, which specially examine the dielectric and ferroelectric properties of the films in the literature. BaRuO3 is an important perovskite ruthenate, which is expected to have the lowest melting a)
Address all correspondence to this author. e-mail: [email protected] J. Mater. Res., Vol. 14, No. 10, Oct 1999
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point among alkaline-earth ruthenates ARuO3 (A ⳱ Ca, Sr, and Ba) with the resistivity ranging from 10−2 to 10−4 ⍀ cm at room temperature.13–15 In this work, we report the fabrication of a BaRuO3/ PZT heterostructure on LaAlO3 substrates by optimizing the dep
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