Growth Reorientation with the Annealing Temperature of SrBi 2 Ta 2 O 9 Films Deposited by PLD
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C11.34.1
Growth Reorientation with the Annealing Temperature of SrBi2Ta2O9 Films Deposited by PLD Ma. P. Cruz1, Jorge J. Portelles2, and Jesús M. Siqueiros1 1 Centro de Ciencias de la Materia Condensada (CCMC)-UNAM. Km. 107, Carretera Tijuana Ensenada. Ensenada, B.C., México. C.P. 22800 2 Facultad de Física-IMRE, Universidad de la Habana, Cuba.
ABSTRACT Films of SrBi2Ta2O9 (SBT) were grown on Pt/TiO2/SiO2/Si substrates by the pulsed laser deposition (PLD) technique. The deposits were made at temperatures between 5700C and 7150C, and post-annealed at 750°C. The films grown at 6100C show a (115) preferentially orientation with a small peaks associated to (00l) planes. At higher deposition temperatures, the (00l) peaks increase their intensity, a tendency that is intensified after the heat treatment at 7500C. However, when the films grown at 590-6100C are heat-treated at 7500C, there is a reduction of the crystallites oriented in the (00l) direction, leading to an enhancement of the polarization, reflected in the maximum value of 2Pr = 9.1 µC/cm2 and a coercive field, Ec, of 52.0 KV/cm. INTRODUCTION SBT ferroelectric thin films have attracted great interest because their possible application in non-volatile random access memories (NVFRAM) [1-9] due to its excellent behavior regarding fatigue free operation up to ~1012 switching cycles, low imprint and relatively low leakage current. SBT belongs to a family of Bi layered-structure perovskite [10] with a highly anisotropic pseudotetragonal structure [11] (a=0.5531nm, b=0.5534nm and c=2.4984nm) that leads to highly anisotropic ferroelectric properties. In this material, the polarization vector is directed along the a-b plane and, in films grown on Pt/TiO2/SiO2/Si(111), a large fraction of the crystallites grow with the a-b planes parallel to the plane of the substrate rendering a relatively low value of the net polarization [8,9]. To achieve the goal of enhancing the projection of the polar vector in a direction perpendicular to the substrate, and for the more general purpose of studying the influence of crystal orientation on the ferroelectric properties of the SBT films, deposits of this material have been made on substrates such as SrLaGaO4(110) [3]; SrTiO3(001),(011),(111) [4]; MgO(110) [5]; and SrLaAlO4(100) [6], however, these substrates are not compatible with silicon-based microelectronics. From a previous study [7], we realized that, keeping the Pt bottom electrodes compatible with microelectronic technology, a reorientation of the SBT films could be achieved using deposition temperatures around 6000C in a combination with a post-deposition heat treatment. As a result, the fraction of crystallites grown with the (00l) direction perpendicular to the substrate was effectively reduced, leading to an enhancement of the measured polarization. The combination of the remnant polarization and the coercive field obtained here is better than that reported in recent publications [12,13] using the same technique and depositing on the same bottom electrodes.
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