Surface Morphology of PZT Thin Films Prepared by Pulsed Laser Deposition
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SURFACE MORPHOLOGY OF PZT THIN FILMS PREPARED BY PULSED LASER DEPOSITION Masaaki Yamazato 1 , Masamitsu Nagano 1 , Tomoaki Ikegami and Kenji Ebihara 'Department of Chemistry and Applied Chemistry, Saga University, I Honjo-machi, Saga, 840-8502, JAPAN Department of Electrical and Computer Engineering, Kumamoto University, Kumamoto, 860-8555, JAPAN ABSTRACT Ferroelectric PbZr0 52Ti 0 480 3(PZT)/YBa 2 Cu 30 7 -(YBCO) heterostructures on MgO substrate were fabricated by KrF pulsed laser deposition. The grid electrode was set between a substrate and target for improvement of surface morphology. The typical PZT layer had excellent ferroelectric properties; remnant polarization of 39 jiC/cm 2, coercive electric field of 41 kV/cm, loss tan 5=0.04, and dielectric constant of 950. X-ray diffraction results show that the films had highly c-axis and (a, b) plane orientation. The full widths at half-maximum (FWHM) of rocking curves was decreased with increasing the applied voltage of grid electrode. Atomic force microscopy (AFM) images of PZT layer showed that the film morphology was improved by using a grid electrode. INTRODUCTION Ferroelectric thin films such as PbTiO 3 , Pb (Zr, Ti) 03 (PZT) and (Pb, La) (Zr, Ti) 03 are widely considered as high permittivity materials in dynamic random access memories (DRAMS), in ferroelectric random access memories (FERAMS) and the gate dielectric candidates in metal/ferroelectric/semiconductor field-effect transistors (MESFETS) [1,21. Moreover, in recent years, electron emission from ferroelectric materials triggered by pulsed electric field has attracted much attention from the view point of various applications such as cold cathodes and emissive plasma display panels [3,4]. PZT/YBa 2Cu3OT_>(YBCO) heterostructures are interesting for various reasons. First, layered perovskite YBCO is compatible with perovskite PZT. Furthermore, it has been pointed out that degradation of remnant polarization due to cycling is significantly less when YBCO contact electrodes are used instead of Pt metal electrode in nonvolatile memory systems. For these electric device applications, it is necessary to obtain thin films with good uniformity and smooth surface morphology. Ferroelectric thin films are fabricated by various techniques such as reactive sputtering, chemical vapor deposition, sol-gel spin-coat and pulsed laser deposition (PLD). PLD is very attractive process for oxide thin film preparation which guarantees the congruent transfer of highly nonthermal eroded target material to the growing film. High initial rate of heating and energetic plasma beam result in high kinetic and internal excitation energies of ablated species assist film growth and promote surface solid state reactions. However, the PLD method has some problems such as existence of particles or droplets [5,6,7,8]. In this paper, we report on a preparation of epitaxial PbZro. 52 Tio.4 80 3 /YBa2 Cu 3 0 7 heterostructures on MgO substrates and improvement of surface morphology by setting a grid
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electrode between a substrate and
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