Interfacial charge and strain effects on the ferroelectric behavior of epitaxial (001) PbTiO3 films on (110) DyScO3 substrates (original) (raw)
Applied Physics Letters, 2013
The effect of stoichiometry on the dielectric properties and soft mode behavior of strained epitaxial Sr 1þx TiO 3þd films grown on DyScO 3 substrates is reported. Direct comparisons between nominally stoichiometric and non-stoichiometric films have been performed through measurements of lattice parameters, temperature-dependent permittivities, second harmonic generation, and terahertz dielectric spectra. The nominally stoichiometric film shows dispersion-free low-frequency permittivity with a sharp maximum and pronounced soft mode behavior. Our results suggest that strained perfectly stoichiometric SrTiO 3 films should not show relaxor behavior and that relaxor behavior emerges from defect dipoles that arise from non-stoichiometry in the highly polarizable strained SrTiO 3 matrix.
Journal of Applied Physics, 2010
Dielectric properties of annealed and as-grown ferroelectric Ba0.5Sr0.5TiO3 (BST) grown by pulsed laser deposition on sputtered BST seed layers on strontium titanate (STO) substrates were investigated at microwave frequencies in the realm of tunability of its dielectric constant as well as phase shifters based on this material. The as-grown layers were nearly fully relaxed with measured lattice parameters nearly identical to those of bulk BST. The tuning of the relative dielectric constant (∼1750 at zero bias at 10 GHz) of the annealed BST was found to be as high as 59% and 56% at 10 and 19 GHz, respectively. The analysis of the loss in the BST results in a measured tan δ of 0.02 for the annealed as well as the unannealed films at a frequency of 18 GHz. Phase shifters also exhibited high tuning with differential phase shift figures of merit of 35 and 55°/dB at a field of 60 kV/cm at 10 and 19 GHz, respectively. Serendipitously, most of the tuning occurs at low fields, and thus we pr...
2010
Perovskite Ba 0.6 Sr 0.4 TiO 3 ͑BST͒ thin films have been grown on Al 2 O 3 ͑0001͒ substrates without/ with inserting an ultrathin TiO x seeding layer by rf magnetron sputtering. X-ray diffraction and pole figure studies reveal that the film with the TiO x layer ͑12-Å-thick͒ is highly oriented along the ͑111͒ direction and exhibits a good in-plane relationship of BST͑111͒ ʈ Al 2 O 3 ͑0001͒. The high frequency dielectric measurements demonstrate that the complex permittivity ͑ = Ј − jЉ͒ is well described by a Curie-von Scheidler dispersion with an exponent of 0.40. The resulting epitaxial BST films show high permittivity ͑ϳ428͒ and tunability ͑ϳ41%, at 300 kV/cm and 40 GHz͒ and their microwave properties ͑1-40 GHz͒ potentially could be made suitable for tunable devices.
Ferroelectric BaTiO3/SrTiO3 multilayered thin films for room-temperature tunable microwave elements
Nanoscale research letters, 2013
Ferroelectric BaTiO3/SrTiO3 with optimized c-axis-oriented multilayered thin films were epitaxially fabricated on (001) MgO substrates. The microstructural studies indicate that the in-plane interface relationships between the films as well as the substrate are determined to be (001)SrTiO3//(001)BaTiO3//(001)MgO and [100]SrTiO3//[100]BaTiO3//[100]MgO. The microwave (5 to 18 GHz) dielectric measurements reveal that the multilayered thin films have excellent dielectric properties with large dielectric constant, low dielectric loss, and high dielectric tunability, which suggests that the as-grown ferroelectric multilayered thin films can be developed for room-temperature tunable microwave elements and related device applications.
Journal of Advanced Dielectrics, 2015
Ba(Mg[Formula: see text]Nb[Formula: see text]O3 (BMN) doped and undoped Ba[Formula: see text]Sr[Formula: see text]TiO3 (BST) thin films were deposited via radio frequency magnetron sputtering on Pt/TiO2/SiO2/Al2O3 substrates. The surface morphology and chemical state analyses of the films have shown that the BMN doped BST film has a smoother surface with reduced oxygen vacancy, resulting in an improved insulating properties of the BST film. Dielectric tunability, loss, and leakage current (LC) of the undoped and BMN doped BST thin films were studied. The BMN dopant has remarkably reduced the dielectric loss ([Formula: see text]38%) with no significant effect on the tunability of the BST film, leading to an increase in figure of merit (FOM). This is attributed to the opposing behavior of large Mg[Formula: see text] whose detrimental effect on tunability is partially compensated by small Nb[Formula: see text] as the two substitute Ti[Formula: see text] in the BST. The coupling between...
Microwave-frequency loss and dispersion in ferroelectric Ba0.3Sr0.7TiO3 thin films
Applied Physics Letters, 2005
We report on broadband microwave-frequency measurements of epitaxial ferroelectric Ba0.3Sr0.7TiO3 thin films that reveal systematic increases in the loss and dispersion as the frequency increases toward 40 GHz. Our analysis provides evidence that the origin of this increased loss and dispersion is the direct coupling of microwave energy into a broad distribution of damped soft-phonon modes. We believe that nanometer-sized polar regions in the thin films play a role in this process, resulting in lattice-dynamical loss mechanisms that extend several decades in frequency below the frequency of the soft mode in these thin-film materials.
Dielectric properties of ferroelectric (Ba0.6Sr0.4)TiO3 thick films prepared by tape-casting
Journal of Electroceramics, 2006
Thick BST films have been fabricated by a tape casting and firing method. Dielectric constants of BST films are changed from 5700 to 7000 at 1 MHz after focused beam annealing. Furthermore, surface morphologies and depth profile of chemistry have been altered after annealing. Especially, Sr atoms diffuse out to the surface, while Ba atoms diffuse into the center. The possibility of the surface alteration of the thick films have been clearly demonstrated in this study, which may applied for the integration of ferroelectrics and other dielectrics and/or conductors for low cost microwave tunable devices.
ACS Applied Materials & Interfaces, 2012
Interface engineered BaTiO 3 /SrTiO 3 heterostructures were epitaxially grown on (001) MgO substrates by pulsed laser deposition. Microstructural characterizations by X-ray diffraction and transmission electron microscopy indicate that the as-grown heterostructures are c-axis oriented with sharp interfaces. The interface relationships between the substrate and multilayered structures were determined to be [001] SrTiO3 //[001] BaTiO3 //[001] MgO and (100) SrTiO3 //(100) BaTiO3 // (100) MgO. The high-frequency microwave (∼18 GHz) dielectric measurements reveal that the dielectric constant and dielectric loss of the nanolayered heterostructures are highly dependent upon the stacking period numbers and layer thicknesses. With the increase in the periodic number, or the decrease in each layer thickness, the dielectric constant dramatically increases and the dielectric loss tangent rapidly decreases. The strong interface effect were found when the combination period is larger than 16, or each STO layer is less than 6.0 nm. The optimized dielectric performance was achieved with the best value for the loss tangent (0.02) and the dielectric constant (1320), which suggests that the BTO/STO heterostructures be promising for the development of the room-temperature tunable microwave elements.
Dielectric response of Ba0.75Sr0.25TiO3 epitaxial films to electric field and temperature
Physics of the Solid State, 2002
The structure and dielectric parameters of the intermediate ferroelectric layer in the (001)SrRuO 3 || (100)Ba 0.75 Sr 0.25 TiO 3 || (001)SrRO 3 heterostructure grown by laser ablation on (001)La 0.294 Sr 0.706 Al 0.647 Ta 0.353 O 3 were studied. Tensile mechanical stresses accounted for the polar axis in the ferroelectric, being oriented predominantly parallel to the substrate plane. The remanent polarization in the Ba 0.75 Sr 0.25 TiO 3 layer increased approximately linearly with decreasing temperature in the interval 320-200 K. The real part of the dielectric permittivity of the intermediate ferroelectric layer reached a maximum ε '/ ε 0 = 4400 at T M ≈ 285 K (f = 100 kHz). The narrow peak in the temperature dependence of the dielectric loss tangent for the Ba 0.75 Sr 0.25 TiO 3 ferroelectric layer, observed for T < T M , shifted toward lower temperatures with decreasing frequency and increasing bias voltage applied to the electrodes.