La doped Ba1−xSrxTiO3 thin films for tunable device applications

Abstract

Pure and La doped Ba0.6Sr0.4TiO3 thin (BST) films were fabricated via the metalorganic solution deposition technique using carboxylate-alkoxide precursors on Pt–Si substrates. The La doping concentration, from 0 to 10 mol %, was found to have a strong influence on the 750 °C postdeposition annealed films material properties. All films possessed a nontextured polycrystalline microstructure with no evidence of secondary phase formation. The pure and 1 mol % La doped films exhibited a uniform microstructure suggestive of a fully developed film at this annealing temperature. Improved dielectric and insulating properties were achieved for the 1 mol % La doped BST thin films with respect to that of undoped BST films. The 1 mol % La doped BST film exhibited a lower dielectric constant, (283 vs 450) and enhanced resistivity (31.4×1013 Ω cm vs 0.04×1013 Ω cm) with respect to that of undoped BST films. The loss tangent and tunability (at 100 kHz) of the 1 mol % La doped BST films were 0.019% and 21% (at E=300 kV/cm), respectively. Films doped at concentrations between 5 and 10 mol % possessed under developed microstructures suggesting that higher annealing temperatures and/or longer annealing times are required. The single phase structure of the 5–10 mol % La doped BST films, combined with the beneficial influence of the 1 mol % La doping on the BST films dielectric and insulating properties, suggest potential for further enhancement of the films material properties after optimization of the thermal treatments for the 5–10 mol % La doped BST thin films.

The effect of Mg doping on the dielectric and tunable properties of Pb0.3Sr0.7TiO3 thin films prepared by sol–gel method

“…As shown in the figure, the dielectric constant rather slowly decreases with frequency up to 1 MHz. On the other hand, the dielectric loss of all samples does not show any appreciable dispersion with frequency up to 1 MHz indicating good interfacial characteristics between films and electrodes [18,19]. The dielectric constant and dielectric loss of Pb 0.3 Sr 0.7 (Ti 1−x Mg x )O 3 thin films at 1 MHz as a function of Mg content are illustrated in the inset of Fig.…”

Self-assembled ferroelectric-dielectric nanocomposite films for tunable applications

“…Figure 4a shows the relationship between volume fraction and nominal molar fraction of CeO 2 in our BaTiO 3 -CeO 2 films on Pt(111). As discussed above, the volume fraction of CeO 2 phase starts to increase with the nominal molar fraction after the solubility limit of Ce in BaTiO 3 . Figure 4b shows the permittivity of the BaTiO 3 -CeO 2 films with different volume fraction of CeO 2 phase.…”

“…We also confirmed that either Ba or Ti doped CeO 2 films do not show any tunable behaviors (see figure 5), indicating that such fine BaTiO 3 nano-fibers in CeO 2 matrix (as observed in figure 3c) indeed act as a tunable element. 3 and CeO 2 resulted in nanocomposite structure, whose orientation was sensitive to the volume fraction of BaTiO 3 and CeO 2 . The inclined (obliquely-oriented) BaTiO 3 -CeO 2 composite film was grown at CeO 2 -rich composition.…”

“…However, for tunable thin film capacitors mostly used at microwave frequencies, the high permittivity of BST results in the great capacitance in the parallel plate configuration, which is not always suitable for applications from the viewpoint of the impedance matching in the circuit [2][3]. The tunable material with a low permittivity can be therefore attractive, although there is a fact that the most of tunable ferroelectric materials show large permittivity above 300.…”

Epitaxial growth, dielectric response, and microstructure of compositionally graded (Ba,Sr)TiO3 thin films grown on (100) MgO substrates by pulsed laser deposition

“…6 For optimum performance of these microwave devices, the grown BST thin films should have large dielectric tunability ([⌬⑀ r /⑀ r ], ⑀ r is dielectric constant), low microwave losses (or high quality factor Q), and low temperature dependence of the dielectric constants in the operational frequency range of the device and in the corresponding temperature range. 11,12 In recent years much progress has been made in the deposition of high-quality BST films and increasing the performance of microwave devices based on BST thin films [13][14][15][16][17] ; however, the application of BST thin films in microwave devices is still hampered by their high microwave losses and the large temperature dependence of the dielectric constants. Furthermore, there is still concern about the reliability of microwave devices over the operating frequency and temperature ranges.…”