Microstructural evolution and piezoelectric properties of thick Pb(Zr,Ti)O 3 films deposited by multi-sputtering method:
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Jong-Jin Choi Department of Future Technology, Korea Institute of Machinery and Material, Chang-Won, Gyeong-Nam 641-831, Korea (Received 19 September 2006; accepted 5 February 2007)
Thick and crack-free Pb(Zr,Ti)O3 [PZT] films were fabricated on platinized silicon substrates by a multisputtering technique. The PZT films were deposited on the Si substrate by the radio frequency magnetron sputtering method using a single oxide target. As the film became thicker, its grain size increased. Therefore, the microstructure of the film was able to be controlled by repeatedly depositing thin layers. In addition, by using a seed layer with the same composition but a much smaller grain size, it was possible to further reduce the grain size of the film. When the film had a small in-plane grain size and a fibrous columnar structure, it was highly resistant to cracking, presumably because of its enhanced strength and structural stability. By exploiting these phenomena, highly dense, crack-free, and thick PZT films were successfully deposited up to a thickness of about 5 m. The evolution of the crystallographic orientation of the film as a function of its thickness was also observed and correlated with the total strain energy of the system.
I. INTRODUCTION
Lead zirconate titanate [Pb(Zr1–xTix)O3; PZT] films have attracted a great deal of attention because of their potential applications in microelectromechanical systems, as well as in nonvolatile ferroelectric random access memories. Sensing and actuation are also possible applications for these PZT films because of their strong piezoelectricity. For actual microelectromechanical systems and other actuation applications, however, relatively thick PZT films with good electrical properties are required.1–3 To fabricate thick and crack-free PZT films, it is very important to understand their microstructural evolution. The fabrication of dense and crack-free thick films is difficult because of the difference in the thermal expansion coefficients between the PZT film and the substrate.4,5 When using solution-based deposition methods such as the sol-gel,6 sol-powder composite,7 or screen printing techniques,8 it is relatively easy to fabricate thick films. However, in most cases, the resulting films
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Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2007.0176 J. Mater. Res., Vol. 22, No. 5, May 2007
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will be porous and, therefore, have low electrical properties. Except for some special applications, high electrical properties are desirable for the PZT system. On the other hand, films deposited using vacuum deposition processes are highly dense, but are very susceptible to cracking because of the thermal mismatch. Generally, the mechanical characteristics of films depend strongly on their microstructure.9–11 The microstructural characteristics of importance include the shape, size, and crystallographic orientation of the grains. The grain size of a film is closely related to its thickness be
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