摘要:

Ba1−xSrxTiO3thin film capacitors have been successfully prepared using rf-sputtering and a metal organic deposition (MOD) method. The structure, microstructure and composition of the BSTO films are presented. Films grown on lanthanum aluminate LAO(100) showedc-axis preferred growth orientation. Broad paraelectric-to-ferroelectric transitions were observed in films prepared by both methods. The tunability of the capacitance by means of an appplied electric field is examined using various capacitor geometries. A decrease in the capacitance exceeding 75% at 77 K was obtained from the MOD deposited films under an electric field strength of 0.3 MV/cm. On the other hand, the tunability of the capacitance in the rf-sputtered films ranged from 5 to 10% at 77 K and at 20 kV/cm, while it exceeds 50% in some films. The results are compared with the predictions of Devonshire's phenomenological theory.

ISSN:1058-4587    

DOI:10.1080/10584589508012564

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

By means of planar multitarget sputtering (001) oriented PbTiO3films were deposited onto highly preferred (100) oriented platinum electrodes on (100) MgO single crystal substrates. Single phase perovskite type films with a degree of (001) orientation between 60% and 70% have been sputtered at substrate temperatures as low as about 470°C. The as grown films exhibit a dielectric constant in the range of 120 to 140 and a pyroelectric coefficient of about 20 nCcm−2K−1at room temperature. The dielectric loss is about 0.01 at frequencies from 1 to 10 kHz. (100) GaAs substrates with an evaporated, highly oriented (100) MgO buffer layer were also used as substrates. However, on these substrates the platinum bottom electrode did not grow highly oriented though the same deposition parameters for Pt deposition as in the case of the single crystalline MgO substrate were used. That's why PbTiO3was produced with a lower (001) preferred orientation. Therefore, the dielectric constant is higher (170–190) and the pyroelectric coefficient is lower (12 nCcm−2K−1).

ISSN:1058-4587    

DOI:10.1080/10584589508012565

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The fabrication of ferroelectric films of modified lead iron niobate by a multiple magnetron sputtering technique with a subsequent rapid thermal annealing at 800°C for 5 seconds is reported. Since the magnetic properties of pure iron preclude its use in magnetron sputtering, a non-magnetic stainless steel was used as one of the target materials resulting in a ferroelectric of composition Pb[(Fe0.7Cr0.2Ni0.1)0.5Nb0.5]O3. The reaction sequence involved in the formation of the ferroelectric perovskite phase has been identified. The films exhibit unsaturated ferroelectric hysteresis loops with a remanent polarization of 15 μC/cm2and a coercive field of 100 kV/cm. The room temperature dielectric constant and dielectric loss at 1 kHz were 640 and 0.1, respectively. The dielectric constant showed a dielectric anomaly as a function of temperature in the form of a broad maximum around 90°C confirming the ferro-para electric phase transition. The films were highly insulating with a room temperature conductivity of ≈1 X−12Ω−1cm−1, and an activation energy of 0.8 eV.

ISSN:1058-4587    

DOI:10.1080/10584589508012566

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

By means of r.f. sputtering of the ceramic targets or pressed powder targets with the chemical constitution of Pb (Zr0.52Ti0.46W0.01Cd0.01) O3the polycrystalline thin ferroelectric films with the perovskite type structure and of thicknessdf= (1–2, 5) × 10−6m on metal (stainless steel, platinum) or ceramic (polycor) substrates have been obtained. In case of thin film deposition on steel substrate and on platinum at low temperatures (Tx< 723 K) the nonferroelectric intermediate layer with the same chemical constitution but with the pyrochlore type structure have been created. Results of the X-ray analysis and dielectric investigations (low frequency dispersion) have proved existence of such a structure. The structural phase transition (P4mm Pm3m) takes place in the thin ferroelectric films. This is a diffuse type transition and the degree of diffuseness depends on the structural perfection of the thin films. The measure of the structural perfection of the thin films was taken to be the mean value of the lattice strains (microdeformations) ⟨ Δd/d⟩ where “d”-interplane distance and the mean dimension (D) of the areas of coherent X-rays scattering (crystallites). With increase in ⟨ Δd/d⟩ and decrease inDthe degree of diffuseness increases. For quantitative and qualitative describing of this dependence in thin PZT films the phenomenological model of diffused phase transition developed earlier by the authors for thin BaTiO3films has been applied. In this case a good agreement between theory and experiment have been achieved for low values of ⟨ Δd/d⟩.

ISSN:1058-4587    

DOI:10.1080/10584589508012567

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Lead scandium tantalate (PST) films with a lead-rich composition were deposited at 500°C by RF sputtering on sapphire substrates coated with Pt and were investigated by cross-sectional transmission electron microscopy. The films consisted almost entirely of the perovskite phase. The grains of perovskite PST had a crystallographic orientation almost parallel to that of the underlying Pt. Some elongated voids were observed. The presence of an interfacial phase, with interplanar spacings consistent with a pyrochlore phase, was demonstrated by electron diffraction and dark-field imaging. The crystallographic orientation of this phase is also nearly parallel to that of the Pt. Energy-dispersive X-ray microanalysis showed that the interfacial phase is lead-deficient. The interfacial phase is irregular in thickness. A reduction in the Pb content of the film leads to a thicker interfacial layer. The implications for the mechanism of growth of PST on Pt and for improvement of the film quality are discussed.

ISSN:1058-4587    

DOI:10.1080/10584589508012568

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The switching, fatigue and rejuvenation phenomena of ferroelectric PZT thin films with differently processed electrode-PZT interfaces and of different thicknesses have been investigated. The ferroelectric contribution to the switching parameters has been isolated from the leakage current contribution, thus allowing the identification of several salient features of the above phenomena. Incorporating our present results with already established properties of PZT thin films, a set of characteristic features of switching, fatigue and rejuvenation is formulated. This set is interpreted using a framework which takes into account the ferroelectric and semiconductor properties of the system. The key issues of the framework are: (i) Strong inhomogeneous built-in electric field exists in virgin films due to contact phenomena. (ii) Extra near-electrode space-charge layers are created during polarization reversal and destroyed by d.c. rejuvenating fields or by the field of fatiguing pulses. (iii) The built-in electric field is affected by these space-charge layers and then, in its turn, governs the evolution of the switching parameters (remanent-polarization, coercive field) of the film during fatigue and rejuvenation. (iv) Near-electrode nucleation of opposite domains is believed to create the extra near-electrode space-charge layers. Therefore, this nucleation seems to be responsible for the fatigue and for the sensitivity of fatigue to the surfacial properties of the film. This approach explains the thickness dependence of the coercive field, the variation of remanent polarization and coercive field with the number of switching cycles, and the rejuvenation phenomena including self-restoring.

ISSN:1058-4587    

DOI:10.1080/10584589508012569

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Highly oriented La-Sr-Co-O(LSCO)/Pb-La-Zr-Ti-O(PLZT)/La-Sr-Co-O heterostructures have been successfully grown on a highly oriented Pt film which was grown on a thermally oxidized Si (SiO2/Si) substrate. The growth of oriented Pt film on the SiO2/Si substrate was made possible through the use of a thin bismuth titanate template layer which isc-axis oriented on the SiO2/Si substrate. The hybrid LSCO/Pt structure effectively reduced the sheet resistance of the electrodes by at least 3–5 times compared with a single LSCO electrode. These ferroelectric PLZT capacitors on Si exhibited symmetric hysteresis loops with very desirable ferroelectric properties. The test capacitors showed reliable performance at both room and high (100°C) temperatures with respect to fatigue, retention, aging, and imprint, suggesting that they can be used as reliable, nonvolatile memory elements.

ISSN:1058-4587    

DOI:10.1080/10584589508012570

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Landau-Devonshire theory1is a useful phenomenological model to describe the properties of ferroelectric phase transitions. Below the transition temperature, the Landau model can be generalized to describe the thermodynamic stability of a ferroelectric crystallite in a bistable polarized configuration, and to predict the response of the crystallite to external fields and charges. The three primary elements to be considered in modeling thin-film ferroelectric devices are the polar response of the ferroelectric itself, the contribution of electrode interfaces, and the interaction of mobile and immobile charged defects and carriers with the ferroelectric and the electrodes. First, the hysteresis properties of a single domain or crystallite are derived. This result is generalized to find the polar response in a polycrystalline film where there may be variations in the size and orientation of the crystallites and in the coercivity, remanence and offset of the domains. After postulating that metal electrodes form Schottky barriers with respect to the ferroelectric, we can then calculate the electric fields and potentials throughout the ferroelectric film. These calculations show that space charges form near the electrodes and the magnitude of the electric field in these regions is large. A further examination of the space charges results in a model for the C-V response of the ferroelectric capacitor, as the C-V response is dominated by space charge effects. The charge concentrations, contact potentials, high-field permittivity, and space charge widths can be extracted from the C-V data. Finally, the interactions between defects and domains leading to domain pinning and fatigue are investigated.

ISSN:1058-4587    

DOI:10.1080/10584589508012571

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor