Phase transformations in rapid thermal processed lead zirconate titanate
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M. Sayer Department of Physics, Queen's University, Kingston, Ontario, Canada, K7L 3N6
I. D. Calder Telecom Microelectronics Centre, Northern Telecom Ltd., Nepean, Ontario, Canada (Received 13 January 1995; accepted 1 September 1995)
The crystallization kinetics of the pyrochlore to perovskite phase transformation in lead zirconate titanate (PZT) thin films have been analyzed using rapid thermal processing (RTP). Sol-gel PZT thin films, fabricated on platinum electrodes, were annealed at 550 °C to 650 °C with hold times ranging from 1 s to 5 min. Glancing angle x-ray diffraction (XRD) was used for depth profiling to identify the location of phases in the films. Transmission electron microscopy (TEM) provided information on grain structure, nucleation, and growth. The phase information was correlated to the ferroelectric and dielectric properties. The perovskite phase nucleated in the pyrochlore phase throughout the film thickness, and at 650 °C the transformation was complete in 15 s. Fast growing (100) PZT nucleated at the platinum and consumed a small-grained matrix until a columnar structure was obtained. A ramp rate of 100 °C/s was sufficiently fast to prevent transformation during heating and allowed the direct application of an Avrami model for transformation kinetics. An activation energy of 610 kJ/mol was determined.
I. INTRODUCTION Thin film lead zirconate titanate (PZT) is a ferroelectric material targeted for integration into microelectronic devices. Thus, it is of technological importance to understand the nucleation and growth kinetics of this material and their influence on the crystallization of these films. This information will then provide control over microstructure for optimization of ferroelectric performance. There have been some recent studies of this material at the microstructural level with little emphasis on the corresponding electrical characteristics.1 As a result the effects of annealing and crystal structure on film properties are not fully understand. Integration of PZT with electrodes on silicon substrates has been the subject of much investigation with platinum and ruthenium oxide being the most successful electrodes to date.1'2 Oriented PZT films are routinely produced on platinum,3'4 and have also been reported for films on Y - B a - C u - O 5 and MgO substrates.6 Thin layers of platinum on ruthenium oxide7 and seeding layers prior to PZT deposition influence the nucleation or suppression of specific PZT orientations and phases.8"10 The evolution of preferred orientation is often discussed as an effect of heat treatment in terms of temperature and time, but also must be analyzed in terms of the competing nucleation and growth processes. J. Mater. Res., Vol. 10, No. 12, Dec 1995
Rapid thermal processing (RTP) has been the subject of several recent studies.11'12 This technique is still being assessed and has yet to be applied to large scale production of ferroelectric thin films. It is of interest to determine if the quality, in terms of physical structure and ferroelectric pro
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