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Ba0.5Sr0.5TiO3 (BST) thin-film capacitor structures with various thicknesses, (50–1200 nm) and different strain conditions (on lanthanum strontium cobalt oxide La0.5Sr0.5CoO3 and strontium ruthenate SrRuO3 buffer layers) were made using pulsed laser deposition, and characterized by x-ray diffraction. The out-of-plane lattice parameter was followed as a function of temperature within the 100–300 K temperature interval. The phase sequence (cubic-tetragonal-orthorhombic-rhombohedral) known to exist in the bulk analog is shown to be strongly affected by both the stress conditions imposed by the buffer layer and the thickness of the BST film itself. Thus, no phase transition was found for the in-plane compressed BST films. On the stress-free BST films, on the contrary, more phase transitions were observed. It appeared that the complexity of structural phase transitions increased as the film thickness in this system was reduced. [ABSTRACT FROM AUTHOR]

Thin film Au/Ba[sub 0.5]Sr[sub 0.5]TiO[sub 3]/SrRuO[sub 3] capacitor structures, with a thickness of dielectric varying between ∼70 and ∼950 nm, were deposited on {001} MgO single-crystal substrates using pulsed laser deposition. Low-field dielectric measurements were performed as a function of temperature and frequency. At all temperatures and frequencies, the dielectric response as a function of thickness was found to adhere reasonably well to the so-called “series capacitor model,” from which nominal “bulk” and “interfacial” capacitance components could be extracted. The bulk component showed weak frequency dependence but strong temperature dependence, with a peak in permittivity and dielectric loss around 250 K and 150 K, respectively. Well above 250 K, reasonable Curie–Weiss behavior was evident. Overall, the extracted bulk component behaved much as would be expected in real bulk ceramics or single crystals lending confidence as to the general applicability of the series capacitor model. The functional behavior of the extracted interfacial capacitance was rationalized as being due to a combination of a thermally independent background, and thermally activated space charge. The activation energy of the space charge (∼0.6 eV) is commensurate with the detrapping of electrons from shallow level traps associated with oxygen vacancies. Importantly, since this component acts in series with the bulk component, the functional analysis performed here implies that the oxygen vacancies lie in a plane parallel to the electrodes. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Pulsed laser deposition was used to grow thin films of several compositions from the Pb(Mg[SUB⅓,Nb[SUB⅔)O[SUB3] - PbTiO[SUB3] (PMN-PT) solid solution as dielectric layers in thin film capacitor structures. They were found to display functional behavior characteristic of relaxors, with the only significant difference between thin film and bulk being a severely reduced dielectric permittivity. Room temperature polarization loops showed a general increase in both the remanent polarization and absolute magnitude of the polarization for a given field with PT content. The electric field-induced strain was primarily examined by in situ x-ray diffraction and although fields greater than 20 MV m[SUP-1] were applied to the films, the maximum observed strain was only ∼0.3%, considerably less than the 1.4% seen in single crystal samples. Piezo-response atomic force microscopy studies were consistent in that the macroscopic effective piezoelectric coefficient d[SUB33], was found to differ from single crystal measurements by an order of magnitude. However, electrostrictive coefficients (Q[SUB33]), were found to be comparable to published values for both PMN- PT single crystals and ceramics, ranging between 1 and 9 ×10[SUP-2]C[SUP-4]cm[SUP2]. Consequently, it seems that the relatively poor strain response in these thin films is intimately linked to the reduced permittivity and not to a fundamental difference in the electrostrictive coefficients between bulk and thin film. [ABSTRACT FROM AUTHOR]

Thin film parallel-plate capacitor structures with Ba[sub 0.5]Sr[sub 0.5]TiO[sub 3] as the dielectric layer were fabricated using pulsed-laser deposition. The thickness of the dielectric was varied between 7.5 nm and 1.4 µm. Low-field measurements of the dielectric constant showed the system to possess a nonzero interfacial capacitance. Since there is considerable debate about the origin of interfacial capacitance, further functional analysis was performed: zero-field dielectric susceptibility information was extracted using Landau-Ginzburg-Devonshire fitting of saturated polarization loops. This analysis revealed that the zero-field dielectric susceptibility extracted from P-E loops does not possess a finite interfacial component. The origin of interfacial capacitance therefore disappears (albeit temporarily) after a significant field has been applied and then removed during the P-E loop measurement cycle. [ABSTRACT FROM AUTHOR]

Strongly oriented thin film capacitors of Pb(Mg[sub 1/3]Nb[sub 2/3])O[sub 3] were made by pulsed laser deposition and found to show a decreased temperature of the dielectric maximum (T[sub m]) relative to bulk. The in-plane strain was measured and found to be compressive, a feature that is normally associated with increased Curie temperatures in conventional ferroelectrics. Other features, such as a more pronounced frequency dependence of T[sub m] in thin films than in bulk, were also noted. An attempt to rationalize these differences by consideration of thermal expansion mismatch between substrate and film is presented. The shifts in T[sub m] are modeled using a semiempirical Landau–Ginzburg–Devonshire model, in which the first coefficient of the thermodynamic potential has been modified to have a quadratic, rather than linear, temperature dependence. The predictions of the model are compared with experimental results from this work and other reports on relaxor thin films extracted from the literature. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Thin film capacitors of Au/Pb(Mg[sub 1/3]Nb[sub 2/3])O[sub 3]–7%PbTiO[sub 3] [PMN–(0.07)PT]/(La[sub 1/2]Sr[sub 1/2])CoO[sub 3] were made by pulsed laser deposition on single crystal {001} MgO substrates. The PMN–(0.07)PT dielectric was perovskite dominated, and demonstrated functional behavior typical of relaxors. Electrostrictive behavior was observed at fields up to 200 kV cm[sup -1], however, the maximum strain was disappointingly low at only ∼0.14%. The macroscopic electromechanical d[sub 33] and Q[sub 33] coefficients were determined using piezo-response atomic force microscopy. At 100 kV cm[sup -1] the macroscopic Q[sub 33] was found to be (2.6±0.2)×10[sup -2] C[sup -2] m[sup 4]. The crystallographic electrostrictive coefficient was determined using in-situ x-ray diffraction and at the same field found to be significantly higher: (4.9±0.2)×10[sup -2] C[sup -2] m[sup 4]. Since these electrostrictive coefficients are of the same order of magnitude as found in single crystal experiments (2.5–3.8×10[sup -2] C[sup -2] m[sup 4]), it appears that the low out-of-plane strain is simply the result of poor polarizability in the thin films. An effective Q[sub 13] component of the electrostrictive tensor was also determined, and found to be ∼-0.32 ×10[sup -2] C[sup -2] m[sup 4]. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]

In ferroelectric tunnel junctions, the tunnel resistance depends on the polarization orientation of the ferroelectric tunnel barrier, giving rise to tunnel electroresistance. These devices are promising to be used as memristors in neuromorphic architectures and as non-volatile memory elements. For both applications, device scalability is essential, which requires a clear understanding of the relationship between polarization reversal and resistance change as the junction size shrinks. Here we show a robust tunnel electroresistance in BiFeO3-based junctions with diameters ranging from 1200 to 180 nm. We demonstrate that the tunnel electroresistance and the corresponding fraction of reversed ferroelectric domains change drastically with the junction diameter: while the micron-size junctions display a reversal in less than 10% of the area, the smallest junctions show an almost complete polarization reversal. Modeling the electric-field distribution, we highlight the critical role of the bottom electrode resistance which significantly diminishes the actual electric field applied to the ferroelectric barrier in the mixed polarization state. A polarization-dependent critical electric field below which further reversal is prohibited is found to explain the large differences between the ferroelectric switchability of nano- and micron-size junctions. Our results indicate that ferroelectric junctions are downscalable and suggest that specific junction shapes facilitate complete polarization reversal. [ABSTRACT FROM AUTHOR]