Preparation of Al Doped PZT Thin Films Using a Sol-Gel Method
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EXPRIMENTAL PROCEDURE To prepare the sol-gel precursor solution, we used trihydrated lead acetate (99.9%), titanium isopropoxide (99.999%), zirconium iso-propoxide (98%) and aluminum iso-propoxide (99.999%) as starting materials, and 2-methoxyethanol as the solvent. The amount of Al substitution for Zr/Ti site was 2.5mol% and 5 mol%, so that the nominal compositions of the solutions were equivalent to those of Pbl l(Zr 0.52Ti 0.48)O1, Pb1 1 ((Zro. 52Tio.48)0 .975Al0 .025)0 3 .and Pb11 ((Zr0 52 . Ti0 .4) 0.95A10 .05)O 3. The method of Blum and
Gurkovitch [4] was modified to prepare the precursor solutions. Figure 1 shows the flow diagram for the preparation of precursor solutions. Trihydrated lead acetate was dissolved in 2-methoxyethanol, and the solvent was boiled to remove the hydration water at 124TC for 12 hours. Required amounts of titanium iso-propoxide, zirconium iso-propoxide and aluminum normal-propoxide were added to the lead acetate solution at 90 'C, and the mixed solution was refluxed
Pb(CH3COO)2-3H20 CH3OCH2CHOH
0.1tool 75ml
Dehydrate at 1241C,i2hr] a+
_
Mi
Ti(0--CH7)4 Zr(0-I-C3HT)4 Al(O-i -C3H7)3
Reflux at 124C,6hr
FComplex alkoxide]
Dilution, o.1nooll1
CH3oCH2CHOH.
Partially hydrolysis
[H20 ]/[TIZr 1-4 Precursor solutio
Coating
Fig. 1 Flow diagram for preparation of precursor solutions.
223 Mat. Res. Soc. Symp. Proc. Vol. 596 © 2000 Materials Research Society
at 124 'C for 6 hours to form complex alkoxide. All procedures were carried out in a dry nitrogen atmosphere. The complex alkoxide solution was cooled to room temperature and was diluted with 2-methoxyethanol to 0.1M. Finally, the diluted solutions were partially hydrolyzed in the proportion of 4 mol water to 1 mol titanium and zirconium alkoxide, and these hydrolyzed solutions were used for thin film preparation. The precursor solutions were deposited onto Pt /Ti /SiO, substrate using a spin coater operated at 3000 rpm. The sequence of spin coating, drying at 115 0C and pyrolysis at 400'C for 3 min was performed several times to control the film thickness. Finally, the samples were fired at 700'C for 15 min in air. The film thickness of the fired samples was 200nm. To evaluate ferroelectric properties, a 0.5mm diameter Pt top electrode was deposited through a metal mask using sputtering. In addition, to simulate FeRAM process and a capacitor cell structure, a 6 inch Pt /Ti /SiO, /Si substrate was used in the film preparation process. Details of the film preparation process are described later. The crystal structure of the thin films was examined with an X-ray diffractometer. The leakage currents of the thin films were measured using a pA meter (HP4140B). A 0.2 V step voltage was applied to the thin film samples and maintained for 3 sec, and then the sample current was measured. The P-E hysteresis curves and fatigue properties were examined using a ferroelectric test system (Radiant Technologies) at ±5V and 5kHz for fatigue measurement. RESULT AND DISCUSSION EfTect of Al doping Figure 2 shows X-ray diffraction patterns of Pb 1
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