Formation of the secondary phases in the Pb-containing perovskite films by pulsed laser deposition
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I. N. Lin Materials Science Center, National Tsing-Hua University, Hsinchu, 30043 Taiwan, Republic of China (Received 31 January 1994; accepted 19 May 1994)
The growth behavior of Pb2+-containing ferroelectric thin films has been systematically examined. The kinetics of the formation of perovskite phase were successfully enhanced by using a material containing no Zr4+-ions, viz., Pbo.95Lao.o5Tio.987503 (PLT) films, and by utilizing platinum coating on silicon substrate. Meanwhile, the formation of TiO 2 phase (rutile) on PLT/Pt(Si) films has been observed and was ascribed to both the outward diffusion of Ti4+-ions from the Ti-layer underneath the Pt-coating and the loss of Pb2+-ions on the surface of the films. The perovskite materials, which were free of either pyrochlore, Zr-rich phase, or TiO2 phase, can be obtained by in situ depositing the PLT films at 450 °C substrate temperature and 1 mbar oxygen pressure. Thus obtained thin films possessed high dielectric constant, sr = 1346 and tan S — 0.071 at 10 kHz, and large charge storage density, Qc = 5.4 ^,C/cm 2 at 50 kV/cm.
I. INTRODUCTION The Pb1^Lax(Zr>,Ti1_J,)1_x/4O3 (PLZT) materials, which possess a broad range of compositions and ferroelectric properties, are widely applied as dielectric, pyroelectric, piezoelectric, and electro-optic devices.1 Recently, the thin film form of PLZT has attracted extensive attention because of its potential to integrate with the semiconductor devices, forming the smart sensors.2 The synthesis of PZT series ferroelectric films is, however, unexpectedly difficult. It is only recently that the films of pure perovskite phase were successfully prepared with the electrical behavior comparable to that of the ceramic form,3"7 but the dielectric constant of the films, which is around s r = 1000, is still inferior to that of the ceramics. The problems come from the difficulty in composition control, which, in turn, is due to the inherent potential for Pb2+-ions loss to occur in the thin film deposition process. Among the popular thin film preparation techniques, such as sol-gel,8 sputtering,9 metal-organic chemical vapor deposition (MOCVD), 10 and pulsed laser deposition (PLD),11"16 the PLD technique possesses overwhelmingly the advantage of easiness in stoichiometric control and efficiency in thin film deposition. It is especially suitable for growing multicomponent oxide thin films. However, the techniques, which have successfully deposited PZT films on single crystal SrTiO 3 n and ysapphire12 substrates, cannot be applied directly to grow PZT films on silicon or Pt-coated substrates.11'13 A large proportion of pyrochlore phase is always present. The materials of good electrical behavior can be obtained on J. Mater. Res., Vol. 9, No. 9, Sep 1994
Si-substrates using the PLD technique only through complicated processing, such as sequential deposition of the ZrO 2 , TiO2, and PbO layers,14 direct deposition of PLT films using PbO-excess single target,15 or postannealing of low-temperature deposited films.16 The potential in Pb2+-ions l
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