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Ba 0.5 Sr 0.5 TiO 3 ͑BST͒ epi layers 500 Å thick with different magnitudes of lattice distortion were fabricated by growing films on various perovskite oxide electrodes. The variations in the misfits between the BST and the bottom electrodes enable the strain manipulation of these BST epi layers. The 500 Å thick BST epi layer on the SrRuO 3 -coated SrTiO 3 ͑STO͒ substrate is almost completely constrained by the SrRuO 3 bottom electrode. The 500 Å thick BST epi layers are partially constrained on the Nb-doped STO, LaNiO 3 -coated STO, and La 0.7 Sr 0.3 MnO 3 -coated STO substrates. A suitable degree of lattice distortion of the BST epi layers is required to obtain a large dielectric constant; this fact is consistent with expectations based on the softening of the soft mode phonon. Variations to the electrical characteristics of the BST epi layers were considered with reference to changes in the degree of the lattice distortion of the BST epi layers.

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Ba 0.5 Sr 0.5 TiO 3 ͑BST͒ films, 600 Å thick and 3 mol % Mn-doped, deposited on La 0.68 Ba 0.32 MnO 3 ͑LBMO͒-coated LaNiO 3 /Pt/Ti/SiO 2 /Si substrates exhibit elongation along the c-axis lattice. A suitable degree of lattice distortion of the BST films increases the dielectric constant. The nonlinear relationship between the dielectric constant and the applied bias voltage indicates that partially strained BST films on the LBMO buffer layers have ferroelectric properties. An LBMO buffer layer deposited at a higher growth temperature is comprised of larger grains, and therefore a rougher surface structure and increased leakage current of the deposited BST film. Ba x Sr 1−x TiO 3 has been extensively investigated as the chargestorage dielectric for use in dynamic random access memory and as an electric-field-tunable element for high-frequency devices. 1,2 Paraelectric Ba 0.5 Sr 0.5 TiO 3 ͑BST͒ in actual devices has many important properties: it is a good insulator with large relative dielectric permittivity and a small dielectric loss near the ambient temperature, as well as a low leakage current density. 3 Recently, considerable effort has been made to increase the dielectric constant and reduce the leakage current of BST thin-film capacitors. The most logical approaches involve varying the film composition and changing the processing conditions. 4,5 However, a common problem is that the dielectric constant of BST thin-film capacitors depends strongly on thickness. As the thickness of the dielectric thin film is reduced to tens of nanometers to meet the requirements of the device, the dielectric constant in the oxide film falls markedly. 6 Defects such as oxygen vacancies that are formed during the preparation of a BST thin film may worsen leakage and breakdown properties. 7 Pt has been extensively adopted as a bottom electrode in perovskite oxide capacitors, 8 and electrical degradation caused by the formation of hillocks at high temperature and the formation of an interfacial layer degrades the performance of capacitors. 9 These critical issues need to be resolved to realize BST films in device applications. Mn-doped BST films grown at an appropriately controlled temperature have satisfactory electrical properties for use in tunable devices. 10,11 The acceptor behavior of substitution of Mn at the Ti site in perovskite is the reduction of the number of conducting electrons in the material, improving the electrical characteristics, such as by reducing the leakage current of the material. In contrast, electromobility and the generation of ionized oxygen vacancies are promoted by acceptor doping, rapidly degrading the ceramic. Doping with donor elements reduces the number of ionized oxygen vacancies and their electromigration toward the cathode of the sample. Recently, conductive perovskite oxides have become attractive as electrode materials in BST capacitors because they have a similar crystalline structure and chemistry. [11][12][13] The perovskite electrodes provide a compatible interface for the dielectric ox...

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The strain-relieved crystalline Ba0.5Sr0.5TiO3 (BST) film on SiO2∕Al2O3 was achieved by combining a molecular-beam epitaxy of BST on Si∕Al2O3 and a post-growth anneal in oxygen at elevated temperatures. The oxidation anneal not only converted the thin Si interlayer into amorphous SiO2 and eliminated the dielectric loss from the Si, but also relieved local strain in the film. The resulting BST film showed promising dielectric properties with 66% tunability and 0.016 dielectric loss, respectively. Additionally, temperature-dependent permittivity of the BST film resembled that of the bulk BST ceramics.

Thin BiFeO 3 ͑BFO͒ films with a thickness of 80 nm were grown on Pt/Ti/SiO 2 /Si͑100͒ substrates at 350-550°C with and without a 100 nm thick LaNiO 3 ͑LNO͒ buffer. The growth of the BFO film with an LNO buffer promotes the appearance of highly ͑100͒-crystallographic features. A high deposition temperature of 550°C yields BFO films with secondary phases. Secondary-ion mass spectrometry depth profiles show no obvious interdiffusion of constituent elements between the BFO and the LNO at growth temperatures of 350-450°C. The buffering of LNO markedly reduces the degree of the surface roughening of BFO films, which is determined by the growth temperature. The spatial distribution of the current image of BFO films grown at 350-450°C on the nanometer scale shows a considerable reduction in the nanostructural leakage current properties of BFO films upon the buffering of LNO because of the effective improvement in the film/electrode interface, chemical homogeneity, crystallinity, and surface roughness of the BFO films. Moreover, impurity phases in the BFO films grown at 550°C act as the dominant conduction path of leakage currents.Enhanced remnant polarization and magnetization compared to a bulk single crystal have been reported in BiFeO 3 ͑BFO͒ thin films. 1,2 Multiferroic BFO thin films are considered among the most promising candidates for ferroelectric random access memories and microelectromechanical systems. The trend toward miniaturization of devices depends on the thinning of films. However, realizing BFO thin films, especially those with a film nanoscale thickness, with the most desired and reproducible electrical properties remains a considerable challenge. 2 Pt is mostly used as an electrode material in ferroelectric capacitors, providing low resistivity and high chemical stability. 3 However, the use of Pt electrodes in the preparation of the ferroelectric layer at a relatively high temperature has some shortcomings. The interface layer caused by atomic interdiffusion and the hillocks are the most important issues. Composite electrodes were recently demonstrated to be effective in enhancing the electrical or crystalline properties of high permittivity oxides from the crystallographic or chemical compatible points. 4,5 Increasing the electrical resistivity of BFO films is very important, and several approaches have been employed to improve their electrical properties, including impurity doping and the use of oxide electrodes. 6,7 Notably, although many efforts have been made to reduce the leakage current in the BFO thin films, understanding leakage phenomena in BFO thin films would benefit greatly from the detection of a leakage current at a spatial resolution that is similar to the length scale of the structural nonuniformities. Such understanding could be exploited in applying BFO thin films in nanodevices. Leakage currents are conventionally measured at microscopic metal-insulator-metal capacitors. 8 Based on this method, the nanoscopic spatial distribution of the leakage current of the insulator layer cann...

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