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U12.10.1

Fabrication and Characterization of Lead Silicate Doped PZT Thin Films Junichi Karasawa, Yasuaki Hamada, Koji Ohashi, Takeshi Kijima, Eiji Natori and Tatsuya Shimoda Technology Platform Research Center, Seiko Epson Corporation, 281 Fujimi, Fujimi-machi, Nagano-ken, 399-0293, Japan ABSTRACT The crystal structure, surface morphology and electrical properties of PbSiOx (PSO) doped Pb(Zr,Ti)O3 (PZT) thin films were systematically investigated. The starting solutions of PSO-doped PZT were prepared by mixing sol-gel solutions of PZT and PSO. RTA-calcined thin films were crystallized by means of an oxygen partial pressure controlled post-annealing process. After the calcining process, lightly doped PZT thin films containing an amount of PSO dopant less than 1.0 at.% exhibit (111)-preferred orientation, and fine grains having a diameter of 50 nm and column-like structure. As the amount of PSO dopant is increased to 5.0 at.%, the (111) peaks becomes obscure and the (100) peaks together with the minor (110) peaks becomes dominant. The column-like structure changes into a plate-like structure having coarse grains whose diameter exceeds 500 nm. Further increasing the level of PSO dopant to 20.0 at.% causes the appearance of a pyrochlore phase having an extremely smooth surface without apparent grains. On the other hand, after the post-annealing process, the pyrochlore phase seen in the heavily doped PZT remarkably disappears, replaced by a perovskite phase together with PSO. The remnant polarization (Pr) gradually decreases as the amount of PSO dopant increases. The break down voltage, fatigue, imprint and other reliability parameters are improved within the proper doping range. INTRODUCTION PZT is one of the most promising ferroelectric materials for use in high-density ferroelectric random access memory (FeRAM). In the early stages of FeRAM development using PZT, some fundamental problems originating from the nature of PZT were pointed out. These problems, which included such things as fatigue, imprint, the difficulty of making the film thinner, have since been overcome by means of PZT modification. For example, the Pb/Zr/Ti composition and the alkaline-earth substitution or donor doping have been optimized, as has the fabrication process, and oxide electrodes such as IrOx. Moreover, recent research[1] has revealed that Bi2SiO5 (BSO) modified PZT thin film has excellent ferroelectric performance in terms of low temperature crystallization, smooth surface morphology and ultra-thin films. In this work, further investigation in silicate modified PZT thin films has been made. So as to investigate the silicon doping effect on PZT crystallinity, surface morphology and electrical properties, PbSiOx (PSO) has been employed as a silicate dopant. Furthermore, an oxygen partial pressure controlled annealing process[2], which is considered to be an effective means of improving the D-E hysteresis curve features, has been employed as a post-annealing process. The detailed results are discussed. EXPERIMENTAL

U12.10.2

The proced