Dielectric and ferroelectric properties of highly (100)-oriented (Na0.5Bi0.5)0.94Ba0.06TiO3 thin films grown on LaNiO3/γ-Al2O3/Si substrates by chemical solution deposition
Graphical abstract
The (Na0.5Bi0.5)0.94Ba0.06TiO3 films deposited by our chemical solution can crystallize at lower temperature. XRD patterns of NBT-BT thin films deposited on (100)-oriented LNO electrode show that the NBT-BT film is highly (100)-oriented with pure perovskite structure when the annealing temperature is higher than 600 °C.
Introduction
Recently, micro-electro-mechanical systems (MEMS) have received considerable attention because they provide significant opportunities for miniaturized mechanical devices based on film materials and silicon technology [1]. An important family of functional materials – ferroelectrics – has been highlighted for integration with MEMS because of their advantageous properties. For example, their piezoelectricity has been used in sensor, actuator and transducer due to a large electric-field-induced mechanical displacement, a rapid response, linearity, and an accurate displacement [2], [3], [4], [5], [6]. Their pyroelectricity has been employed in infrared sensors because it can be operated at room temperature and meanwhile has good sensitivity and rapid response [2], [7], [8], [9]. At present, lead zirconate titanate [Pb(Zr,Ti)O3) or PZT] is the most popular ferroelectric film due to its excellent piezoelectric and pyroelectric properties. However, the toxicity of lead oxide and its high vapor pressure during processing have led to a demand for alternative lead-free piezoelectric materials. (Na0.5Bi0.5)xBa1−xTiO3 (NBT-BT) is a promising lead-free ferroelectric [10], [11], [12], [13]. The ferroelectric and piezoelectric properties of NBT-BT in bulk form have been extensively studied. It was reported that the bulk form of NBT-BT with a composition near morphotropic phase boundary (MPB) (x = 0.06) shows best ferroelectric and piezoelectric properties [10]. The piezoelectric constant of the NBT-BT ceramics with the MPB composition can reach up to 125 pC/N [10], the (100)-oriented crystals grown by spontaneous nucleation method showed a piezoelectric constant of d33 = 450 pC/N and electric-field-induced strain up to 0.25% [12]. Meanwhile, good pyroelectric properties (pyroelectric coefficients Pi = 3.9 × 10−4 C m−2 K−1) for MPB composition have also been achieved [14], which possibly result from the large spontaneous and remnant polarization (Pr = 40 μC/cm2) and lower depolarization temperature (Td = 100 °C) of this material [10]. NBT and NBT-KBT films have been prepared by chemical solution deposition (CSD) process [15], [16], [17], [18]. However, until now, NBT-BT in thin film form prepared by CSD process was few investigated. In this paper, we prepared a precursor chemical solution of NBT-BT with MPB composition which can be used for film deposition. The dielectric and ferroelectric properties of the highly (100)-oriented (Na0.5Bi0.5)0.94Ba0.06TiO3 (NBT-BT 94/6) films grown on LaNiO3/γ-Al2O3/Si substrates were investigated.
Section snippets
Experimental
Si(100) substrate with an epitaxial γ-Al2O3(100) insulator layer deposited using a CVD method as reported in our previous paper was used as the substrate [19], [20], [21]. The thickness of γ-Al2O3 layer is about 10 nm. The γ-Al2O3 film has low leakage current, higher dielectric constant (relative dielectric constant ɛr about 7.5) than SiO2 (ɛr about 4), and low interface state density, which make it a good gate-insulator material [22]. Meanwhile, the γ-Al2O3 film has good chemical and thermal
Results and discussion
Transparent and stable precursor chemical solutions of BaTiO3 (BTO) and (Na0.5Bi0.5)TiO3 (NBT) were first prepared with reference to previously reported chemical solution deposition (CSD) processes for BTO and NBT [15], [16], [17], [18], [27], [28], respectively, as shown in Fig. 1. However, when then these two transparent solutions mixed, a white precipitation will appear after stirring. In order to uncover the formation mechanism of the white precipitation, we add distilled water into this
Conclusions
A chemically modified (Na0.5Bi0.5)0.94Ba0.06TiO3 solution was prepared by using barium acetate, nitrate of sodium, nitrate of bismuth, and Ti-isopropoxide as raw materials; and acetic acid, 2-methoxyethanol, and acetylacetone as solvent or ligand. A white precipitation appears during the preparation, it is analyzed to be Ba(NO3)2. We found that ethanolamine is very effective to prevent from formation of Ba(NO3)2 or dissolve it. A transparent and stable (Na0.5Bi0.5)0.94Ba0.06TiO3 chemical
Acknowledgements
This work was supported in part by Creation and Support Program for Start-ups from Universities from the Japan Science and Technology Agency and Cooperation Program on Innovative Technology and Advanced Research in Evolutional Area (Toyohashi Area) from the Ministry of Education, Culture, Sports, Science and Technology.
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