SEM and Auger studies of a PLZT thin film
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The microstructure and the composition profile of lead lanthanum zirconate titanate thin film fabricated using the sol-gel method were analyzed using the scanning electron microscope and scanning Auger microscope. The PLZT thin film consists of micron-scale spheroidal perovskite grains and nano-scale pyrochlore grains. The perovskite grain has a higher lead and lower oxygen and zirconium contents than the pyrochlore grain. The Auger spectra of the two phases were similar except for energy shift and extra fine structure of oxygen peaks. The Auger depth profile and SEM observation of the cross-sectional fracture surface showed higher perovskite content near the interface between PLZT and ITO films than the surface of the PLZT film.
The lead zirconate titanate (PZT) and lead lanthanum zirconate titanate (PLZT) thin films have been studied extensively due to their large piezoelectric constants and electrooptic effects.1 PZT and PLZT have been known to have two crystalline phases: the pyrochlore phase being stable at relatively low temperature and the perovskite phase at relatively high temperature. The PZT and PLZT thin films are usually composed of the amorphous phase after deposition. During normal heat treatment of the amorphous thin films, both pyrochlore and perovskite phases were crystallized in the films. A typical microstructure of the PZT and PLZT thin films consists of micron-scale spheroidal perovskite particles and nano-scale pyrochlore grains.2-3 The perovskite phase has tetragonal, rhombohedral, or orthorhombic structure, depending on the composition and chemical formula of ABO 3 . The pyrochlore phase has a cubic fluorite structure and the chemical formula of A 2 B 2 O 7 . 4 Since the pyrochlore is centrosymmetric, it does not show ferroelectric properties. In order to use the PZT and PLZT films in electronic and electrooptic applications, the films must have a higher perovskite phase content because only the perovskite phase shows the excellent electrical and electrooptical properties that are needed for practical applications. The objectives of the present study are to investigate the microstructure of a typical PLZT thin film, using the electron microscope, and to determine the differences between the perovskite phase and the pyrochlore phase in the microstructure. PLZT (9/65/35) thin films were fabricated using spin coating of the metallo-organic solution on ITO (Indium Tin Oxide) coated Corning 7059 glass substrate and heat-treated at 600 °C for 2 h. An explicit processing of the PLZT thin film using the sol-gel method is described in Ref. 3. J. Mater. Res., Vol. 8, No. 2, Feb 1993
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Figure 1 shows SEM images of the microstructure of a typical PLZT thin film. The normal SEM image la)
(e)
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PLZT
GLASS
FIG. 1. SEM images of the microstructure of a typical PLZT thin film: (a) a secondary electron image, (b) a backscattered electron image of the same area as (a), (c) a high magnification image of A in (a), (d) a high magnification image of B
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