Crystallization Dynamics of Ferroelectric PZT(52/48) Thin Film Prepared by Reactive Cosputtering on Pt On Si(100)
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cosputtering technique. The multitarget cosputtering system used here and optimized sputtering 5 conditions for the growth of stoichiometric PZT(52/48) films are fully described elsewhere. ,6 The films were annealed at the temperature range of 450-800 'C for 30 min to 3 h in oxygen atmosphere. The structural investigation was then performed using a Rigaku DMAX-3C glancing angle x-ray diffractometer. Changes in the surface morphology were observed using a Hitachi S800 scanning electron microscope (SEM) equipped with a field emission gun. Cross-sectional transmission electron microscopy (TEM) samples were prepared using a standard method. Sliced sections were mechanically polished, followed by dimple grinding. The samples were then thinned to electron transparency using ion milling with 4 kV Ar÷ ions in a Gatan Model 600 ion thinning instrument of dual type. Transmission electron microscopy was performed using a Philips CM20 scanning transmission electron microscope operating at 200 kV. Cross-sectional TEM micrographs and selected area electron diffraction patterns were recorded for each sample prepared under different post-annealing conditions. RESULTS AND DISCUSSION As-deposited PZT films were amorphous to x-rays and the films were subjected to an postannealing treatment step to crystallize into the proper ferroelectric phase, i.e. perovskite phase. The film composition (Zr/Ti ratio) obtained by energy dispersive x-ray microanalysis was 52/48. As shown in Figures 1 and 2, the crystallization of as-deposited PZT film is a function of annealing temperature and holding time. Figure 1 illustrates that the amorphous PZT films were first crystallized into a pyrochlore phase of Pb 2(ZrTi)2O7 -_type for annealing temperature as low as 500 'C for 4 hours at substrate temperature of 200 'C. However, 30 minutes of annealing at 550 'C was required for the initial formation of perovskite phase (Figure 2). These results indicate that the transformation process from the amorphous to the crystalline state in the PZT films is very sluggish at lower temperatures and does not proceed at a measurable rate, as observed in most nonmetallic materials. 7 This implies that the growth rate strongly depends on 50lk .
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Figure 1. X-ray diffraction patterns of 0.72 jtm-thick PZT(52/48) film deposited on Pt/Ti/Si0 2/Si at substrate temperature of 100 'C (a), 200 0C (b) and post-annealed at temeprature of 450 'C (c), 500 'C (d), 550 'C (e), 600 'C (f), 750 'C (h) and 800 'C (i) for 4 hours.
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Figure 2. X-ray diffraction patterns of 2.1 gm-thick PZT(52/48) film annealed at 550 'C for 30 min (a), 1 hour (b), and 4 hours (c) temperature with the dependence being of an Arrhenius type. The continuous microstructural evolution of the 0.72 lm-thick PZT(52/48) film at different annealing temperatures is shown in Figure 3. The as-deposited film has a dense surface structure 5 with gra
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