Orientation control of lead zirconate titanate film by combination of sol-gel and sputtering deposition
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Highly oriented lead zirconate titanate (PZT) films were fabricated on a platinized silicon substrate using a combination of sol-gel and radio frequency (RF) magnetron sputtering deposition methods. A sol-gel derived PZT layer highly oriented to the (100) plane was deposited as a seed layer, and PZT with the same composition then was deposited on the seed layer by RF-magnetron sputtering. The film deposited on the seed layer showed a strong (100) preferred orientation, while the film deposited without the seed layer showed a (111) preferred orientation. Furthermore, a thick PZT film of up to 4 m was able to be deposited without cracks by using the seed layer. The piezoelectric property of the (100) oriented film was much better than that of the (111) oriented film.
I. INTRODUCTION
Lead zirconate titanate (PZT) films have attracted much attention for their potential applications in microelectromechanical systems (MEMS) as well as in nonvolatile ferroelectric random access memories (FeRAM) due to their excellent ferroelectric and piezoelectric properties. The strong piezoelectric response of PZT films makes electromechanical sensing and actuation possible. For actual MEMS applications, relatively thick PZT films with high piezoelectric properties are required.1,2 According to theoretical calculations,3,4 the piezoelectric properties of the (100) oriented rhombohedral PZT film near the morphotropic phase boundary (MPB) are superior to those of the (111) oriented film. Park et al.5 also reported that the piezoelectric properties of the (100) oriented rhombohedral single crystal near the MPB were superior to those of the (111) oriented rhombohedral single crystal. Therefore, the (100) oriented rhombohedral phase is expected to have excellent piezoelectric properties. Because it generally is difficult to control the orientation of the film in a reproducible manner when using a sputtering procedure, the sol-gel method is adopted to control the orientation of the film. The sol-gel method has the advantage of allowing the crystallographic orientation to be controlled reproducibly,6 but there is also a risk of contamination and the generation of interfaces among the layers due to the repeated deposition required
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Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2005.0030 J. Mater. Res., Vol. 20, No. 1, Jan 2005
to fabricate thick films. When employing a seed layer to control the orientation, differences in the compositions of the seed layer and that of the PZT film could cause additional problems such as electrical degadations.7 In this study, PZT thick films with high quality and a strong (100) preferred orientation were fabricated using a combination of the sol-gel procedure and sputtering techniques. The sol-gel and sputtering methods, which were used to control the texture and to deposit the film homogeneously, respectively, were combined to make thick films without any compositional differences between them. In other words, thick PZT films were deposited by RF-magnetron sputter
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