Preparation and Characterization of Pb(Zr, Ti)O 3 Thin Films by Metalorganic Chemical vapor Deposition Using a Solid Del
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Pb(Zr,Ti)O3 (PZT) thin films were deposited on Pt/SiO2/Si substrates by metalorganic chemical vapor deposition using solid delivery system. The effects of deposition parameters such as the substrate temperature, the concentration of Pb precursor in the precursor mixtures, and the reactor pressure on the structural and electrical properties of PZT thin films were investigated. To obtain single-phase PZT thin films, the optimal range of the substrate temperature should be between 600 and 650 °C. The PbO content in PZT thin films was proportional to the fraction of Pb in the precursor mixture below 550 °C, but it was independent of the fraction of Pb in the mixture above 600 °C. With the increment of the reactor pressure, Zr contents in PZT thin films were increased, and the Pb/(Zr + Ti) ratio became more stoichiometric so that the ferroelectric properties were improved.
I. INTRODUCTION
Recently, ferroelectric thin films have been extensively investigated to apply to ferroelectric random-access memory (FRAM).1 Pb(Zr,Ti)O3 (PZT) is considered to be one of the very promising materials because of the large remanent polarization and relatively low temperature deposition process. To deposit PZT thin films, various techniques have been used, such as sol-gel, 2 sputtering,3 laser deposition,4 and metalorganic chemical vapor deposition (MOCVD).5 Even though the current low-density FRAM devices are fabricated using the solgel-derived or sputtered PZT thin films, the requirement for higher integration densities makes the MOCVD technique more desirable due to its excellent step coverage and amenability to a large wafer-size scaling. However, it is rather difficult to deposit high-quality multicomponent oxide films by MOCVD technique using conventional bubbler-type delivery system. This is because at the elevated vaporization temperature the metalorganic precursors gradually deteriorate. In this paper, a solid delivery technique,6 in which the mixture of solid metalorganic precursors was flashsublimed into MOCVD growth chamber, was used to obtain the reproducible transport of the vapor of metalorganic precursors to the film growth surface and to deposit stoichiometric PZT films. To acquire single-phase perovskite PZT thin films and good ferroelectric properties, the composition of the films, especially, the Pb/ (Zr + Ti) and Zr/Ti ratios, should be precisely controlled. In this experiment, the compositional control of the films 1284
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J. Mater. Res., Vol. 15, No. 6, Jun 2000 Downloaded: 18 Mar 2015
was attained by changing the ratio of the solid precursors in the mixture. The primary process parameters, such as the substrate temperature, the fraction of Pb precursor in mixture, and reactor pressure, were systematically changed to acquire single-phase perovskite PZT thin films. II. EXPERIMENTAL PROCEDURE
Figure 1 shows a schematic diagram of the solid source MOCVD system. The details of solid delivery system used in this experiment have already been reported elsewhere.7 For the deposition of PZT t
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