Low Temperature Crystallization of PbTiO 3 Thin Film by Excimer Laser Irradiation
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ABSTRACT Lowering the fabrication temperature for ferroelectric films is very important not only for silicon monolithic circuits but also for various substrates. Amorphous PbTiO 3 thin films were prepared on glass substrates using ArF pulsed laser deposition (PLD). They were subsequently treated by a laser-induced phase transformation technique to achieve a perovskite structure. After irradiation by an ArF pulsed laser with an energy density 50mJ/cm 2 in air, the films crystallized into the perovskite structure. It was possible to maintain the substrate at room temperature during the whole fabrication process. The structure, morphology and composition of the films were characterized by X-ray diffraction diffractometry (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX), respectively. The surface of film irradiated with a laser was often rather rough and peeled off everywhere. It was necessary to control the number of laser pulses to avoid damaging the films. The effects of chemical composition and fabrication temperature are also discussed.
INTRODUCTION In recent years, considerable attention has been paid to Pb-based ferroelectric thin films such as PbTiO 3 for wide applications to pyroelectric devices, optoelectric devices, dynamic random-access memories and nonvolatile memories. A variety of methods have been used for deposition of PbTiO 3 thin films. Generally, the crystallization of PbTiO 3 films requires high processing temperatures of about 600 'C. This high temperature processing condition has created difficulties for the integration of ferroelectric films with silicon monolithic circuits or various substrates such as glasses. Decreasing the temperature for ferroelectric film fabrication is required. Some workers tried to decrease fabrication temperature by laser irradiation for Pb-based ferroelectric films. Hayashi et al. and Tabata et al. obtained lower fabrication temperatures in evaporation method and laser ablation, respectively [1,2]. These two attempts used in situ crystallization. On the contrary, Lu et al. and Xiong et al. tried a post deposition laser-induced 557 Mat. Res. Soc. Symp. Proc. Vol. 596 © 2000 Materials Research Society
phase transformation technique [3-5]. The latter method has potential advantages in selective crystallization so on. In this paper, we report the crystallization of PbTiO 3 thin films by irradiation with an ArF excimer laser after deposition. The effects of chemical composition and fabrication temperature are also discussed. EXPERIMENT PbTiO 3 films, 250 nm thick, were deposited onto silica glass substrates using pulsed laser deposition. The ablation ArF excimer laser was focused on the target at an energy density of 2 J/ca with a repetition rate of 5 Hz. The working gas was pure oxygen with the gas pressure maintained at 0.1 Torr. The silica glass substrate was located at a distance of 3 cm from the target. Substrate temperature was maintained at room temperature or 300 'C. Two kinds of targets were prepared to adjust the composi
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