Preparation And Properties Of NBT-KBT-100x Piezoelectric Thin Films

Lead-free piezoelectric materials are desired inevitably as alternate materials of lead-based materials for the sake of environmental protection and biocompatibility, because the lead toxicities of producing, using and recycling are problematic for devices associated with lead-based materials. Bismuth sodium titanate (Na0.5Bi0.5TiO3, NBT) is A-bit complex perovskite-type relaxor ferroelectrics, and it is considered as one of the major lead-free piezoelectric materials because of the strong ferroelectricity and high Curie temperature. However, NBT ceramic is difficult to polarize because of their large coercive field and high leakage current, and it exhibits low piezoelectric properties. In order to improve the performance of NBT ceramic, NBT was modified by other materials such as K0.5Bi0.5TiO3 and BaTiO3, and morphotropic phase boundary (MPB) may exitst in the modified NBT-based solid solution. The previous reserach is revealed that NBT modified K0.5Bi0.5TiO3 solid solution ((1-x) Na0.5Bi0.5TiO3-xK0.5Bi0.5TiO3, NBT-KBT-100x) is of a larger increase of piezoelectric and dielectric properties near MPB region. The miniaturization of electronic devices, the new micro-electromechanical systems (MEMS) and the concept breakthrough of electronic devices promote the development in materials research field from bulk to thin film. In this paper, the preparation and characterization on the properties are studied for NBT-KBT-100x thin films, and the main contents and results are shown as follows:1. The development, the basic properties and applications of piezoelectric materials are summarized in the introduction. In addition, it is focused on the current research state of NBT-based materials which is of good piezoelectric properties and widely applications. The topics and main work of this paper are proposed combining with the preparation technology of thin film such as megnetron sputtering, pulsed laser deposition (PLD) and chemical solution deoposition (CSD).2. The content, LaNiO3 (LNO) and Pt bottom electrodes are chosen to study the content and bottom electrode effects on the microstructure and properties of NBT-KBT-15 thin films, because the microstructure and properties of the thin films are closely related with the bottom electrode and MPB of NBT-KBT-100x ceramics exists in the range of content 0.16-0.20. NBT-KBT-100x thin films near MPB with x=0.15, 0.18, 0.20 and 0.25 are prepared on LNO and Pt bottom electrodes by CSD method. The measure technologies and character methods on thin film are introduced. 3. The effects of LNO and Pt bottom electrodes on the crystal structure, surface microstructure, leakage current, ferroelectric, dielectric and piezoelectric properties of NBT-KBT-15 thin film are investigated by XRD, AFM, ferroelectric tester, impedance analyzer and scanning probe microscopy. The results show that LNO bottom electrode is beneficial to not only improve the crystallinity of NBT-KBT-15 thin film, but also lower leakage current and the dielectric properties. In addition, the effective piezoelectric coefficient d33eff is enhanced.4. The effects of KBT content x (x=0.15, 0.18, 0.20 and 0.25) on the micstructure and properties of NBT-KBT-100x thin films are also investigated, and the results show that NBT-KBT-15 thin film present the lowest leakage current, the highest dielectric and piezoelectric constant. Additionally, the nano-indentations of NBT-KBT-15 thin film are performed by nanoindent and the elastic modulus and hardness of the thin film were obtained.