Effect of Bottom Electrodes on Structural and Electrical Properties of Laser Ablated SrBi 2 Ta 2 O 9 Thin Films
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Effect of Bottom Electrodes on Structural and Electrical Properties of Laser Ablated SrBi2Ta2O9 Thin Films Rasmi R. Das, W. Pérez, P. Bhattacharya, and Ram. S. Katiyar Department of Physics, University of Puerto Rico, San Juan PR 00931-3343 USA
ABSTRACT We have grown SrBi2Ta2O9 (SBT) thin films on various bottom electrodes such as Pt/TiO2/SiO2/Si (Pt) and LaNiO3/Pt/TiO2/SiO2/Si (LNO) substrates. The substrate temperature and oxygen pressure for the SBT film was maintained at 500 oC and 200 mTorr. As-grown films were post-annealed at a temperature of 800 oC. X-ray diffraction studies revealed that as-grown films were amorphous and crystallized to single phase after annealing. The difficulty of obtaining lowest Raman modes of SBT on platinized silicon substrate was overcome by using conducting oxide electrodes. Films grown on platinized silicon showed maximum value of remanent polarization (2Pr ~ 21.5 µC/cm2) with coercive field (Ec) of ~ 67 kV/cm. The degradation of ferroelectric properties of the films was observed with the introduction of 50 nm conducting LaNiO3 electrode at the interface of Pt and SBT film, which was attributed to high resistivity of the oxide electrode layers. Leakage current density was studied with the consideration of the Schottky emission model. The barrier height of the films grown on Pt and LNO were estimated to be 1.27 eV and 1.12 eV, respectively. The reduction of barrier height was attributed to the lower work function of the LNO electrode. INTRODUCTION Bismuth layered ferroelectric SrBi2Ta2O9 (SBT) has emerged as an attractive material for non-volatile memory applications due to its fatigue endurance up to 1012 switching cycles, lower operating voltage and lower leakage current density on metal electrodes [1]. The crystal structure of this compound is composed of two SrTa2O7 unit cells sandwiched between (Bi2O2)2+ layers along pseudo-tetragonal c-axis [2]. There have been a large number of reports to increase the polarization and reduce the crystallization temperature of SBT by preparing non-stoichiometric SBT or by growing SBT thin films on oxide electrodes [3,4]. Normally, the films on metal electrodes exhibit lower leakage current density in comparison to oxide electrodes. Most of the research work on SBT has been reported for better ferroelectric properties at growth or annealing temperatures of 750-800 oC. Due to higher formation temperature of SBT and in order to avoid the interdiffusion of Bi into Pt, it is necessary to grow SBT at lower processing temperature or to grow a interfacial conducting oxide layer between Pt and SBT without sacrificing its ferroelectric properties. The successful integration of SBT into silicon technology requires a detailed understanding of the electrical properties of this material. Low temperature processing of SBT on LaNiO3 electrode has been reported by Hu et al [3]. But the effect of LaNiO3 electrode on top of Pt and its influence on leakage current behavior of SBT thin films has not been addressed. In this report, we study the influence of inter
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