Reversible and Switching Parts of Polarization in PZT Films
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Mat. Res. Soc. Symp. Proc. Vol. 596 © 2000 Materials Research Society
solutions of Zr and Ti methoxyethoxides were obtained by direct anodic dissolution of corresponding metals [9]. The effects of the different conditions (e.g. Pb acetate dehydration techniques, annealing procedure, Pb excess in the precursor etc.) were discussed previously [8,9]. The ratio of Zr/Ti in the precursor was 53/47 and 10% excess of Pb was used, to optimize the stoichiometry of the film. The second precursor was prepared from the PZT polymer produced by Chemat Technology, Inc. (PZT9103) and was simply a 15 vol% solution of the polymer in 1-propanol. This polymer has Zr/Ti ratio of 52/48, which is very close to that of the sol-gel precursor. The main advantage of the polymeric precursor is higher stability. It was possible to store polymer by itself, or as the solution in 1-propanol for 2 years in a sealed bottle without any significant changes. The results reported earlier show that the quality of the films and electrical properties are similar for films obtained for either the polymeric or sol-gel precursor [7]. Due to higher stability, the polymeric precursor was used for preparation of the films for this investigation. The films were deposited by spin coating (4000 rpm, 20s) on Si-SiO 2 -Ti-Pt substrates,
dried at 70'C for 30 min followed by 150 0C for 1 hour. The films were than annealed at 300NC for 1 hour followed by 450'C for 3 hours to form the oxide film. The resulting thickness was 0.25 ýim for one deposition. Multiple depositions were used only for XRD analysis (5 depositions, -1.2 tim). Different annealing temperatures were used to investigate the transition from the pyrochlore to tetragonal phase. The results of the XRD measurements are shown in the Fig. 1. It can be seen, that the transition takes place at 650'C which is similar to sol-gel films. To insure the formation of single phase perovskite structure, all the films were annealed to at least 650'C prior to making electrical measurements. Platinum contacts were deposited on the
PZT on Pt substrate, various annealing temperatures 100
211
S200 Pt
20
25
30
35
40
45
50
55
0P4
60
220 p
210
65
70
'
20 [degrees] Fig. 1. XRD data for PZT films prepared from polymeric solution (Zr/Ti=52/48).
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surface of the films by magnetron sputtering through a mask. The diameter of these contacts was 100Im with a thickness of 0.2 jim. No further annealing occurred after the deposition of the top Pt electrode. A special pulsing technique was used for the electrical investigation. This technique is based on the fact that the relaxation time for the ferroelectric polarization is very small (in the order of nanoseconds) and the relaxation time of the space charge is large (in the order of seconds, or even minutes). As a result, if the testing period ranges from microseconds to seconds and the sample is returning to its initial polarization state after testing, it is possible to investigate ferroelectric polarization without changes in the space charge distribution. The
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