The Microstructure, Phase and Ferroelectric Properties of PZT Thin Films on Oriented Multilayer Electrodes
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ABSTRACT Three kinds of oriented electrodes of Pt, Ir and Pt/Ir electrodes were prepared using electron beam evaporation techniques for deposition of PZT thin films. An oxide MOCVD reactor with liquid delivery system was used for the growth of PZT thin films. [Pb(thd) 2], Zr(TM-D)4 and Ti(IPO) 4 were dissolved in a mixed solvent of tetrahydrofuran or butyl ether, isopropanol and tetraglyme to form a precursor source. The deposition temperature and pressure were 500 650'C and 5 - 10 Torr, respectively. The experimental results showed PZT thin film deposited on various electrodes had different phase formation, microstructure and ferroelectric property. The X-ray patterns showed the perovskite phase of PZT was formed on both Ir and Pt/Ir electrodes at 550'C. The grain size of the PZT thin film increases after a further, higher temperature annealing. The as-deposited PZT thin film on Pt electrode exhibits pyrochlore phase at 550'C. The phase is transformed to perovskite phase after 650'C annealing. The experimental results also indicated that the MOCVD PZT thin film on Pt/Ir exhibits better ferroelectric and electrical properties compared to those deposited on Pt and Jr electrodes. A 300 nm thick PZT thin film on Pt/Ir electrode has a square, well saturated, and symmetrical hysteresis loop with 2Pr value of 40 PC/cm 2 and 2Ec of 73 kV/cm at an applied voltage of 5 V. The hysteresis loop of the PZT thin film is almost saturated at 2 V. The leakage current of the film is 6.16 x 10-7 A/cm 2 at 100 KV/cm. The electrode effects on ferroelectric properties of PZT thin films also have been investigated. INTRODUCTION The remanent-polarization states of ferroelectric capacitors are of great interest for nonvolatile storage of digital data [1-5]. The recent approach to ferroelectric memories is to integrate the ferroelectric memory capacitor into a random access memory circuit on an integrated circuit to convert semiconductor RAM to a nonvolatile form. The most popular ferroelectric material under investigation for nonvolatile memory applications is PbZrxTi 1-xO3 (PZT). This material exhibits high Curie temperature, large remanent polarization, long charge retention time, and radiation immunity [6-8]. In addition to non-volatile memory applications, PZT thin films have also been proposed for pyroelectric detectors, piezoelectric, and electro-optical devices [9]. Most of the studies on Ferroelectric Random Access Memories (FeRAM) are concentrated on the memory structure with one transistor and one capacitor (iTIC). The capacitor is made by a thin ferroelectric film sandwiched between two conductive electrodes. For ITIC FeRAM application, the fatigue problem of the ferroelectric capacitor is one of the major obstacles for commercialization. Research is being conducted to improve the fatigue property of PZT material using conductive oxide electrodes such as Y-Ba-Cu-O, RuO 2 , La-sr-Co-O, etc. as well as introducing doping material such as La and Nb donors into the film [10-12]. The electrode has significant effect on the ferroelect
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