Volume 87, Issue 11, 01 June 2000
Index of content:
- DIELECTRICS AND FERROELECTRICITY (PACS 77)
87(2000); http://dx.doi.org/10.1063/1.373490View Description Hide Description
The crystal structure and electrical properties were investigated for (001)- and (116)-oriented (SBT) thin filmsdeposited on and substrates, and and substrates, respectively. Both oriented SBT films were epitaxially grown with high crystal perfection, and twinning existed in the (116)-oriented one. Both oriented SBT films were found to form lattice displacements to relax the stress. The interface of the (001)-oriented film did not include misfit dislocations, defects, and an interfacial layer, and that of the (116)-oriented film included the lattice strain contrast due to an irregular atomic arrangement. The electrical property of the SBT film shows anisotropy of the ferroelectricity along the c- and a-axis directions; the remanent polarizations of the (001)- and (116)-oriented SBT films were 0 and 10.5 μC/cm2, respectively.
87(2000); http://dx.doi.org/10.1063/1.373491View Description Hide Description
Ferroelectric thin films of bismuth-containing layered perovskite have been prepared using the metalorganic decomposition method. The effect of both Sr and Pb content on the crystal structure,microstructure, and ferroelectricproperties of films was investigated. A maximum remanent polarization of was obtained for the film with 20 mol % Sr-deficient composition as prepared at which could be the compromising effects of Sr content on both grain growth and second phase formation of The substitution of Pb for Bi is accompanied by the occurrence of oxygen vacancies to compensate the charge balance, which is responsible for grain growth mechanism in films. Fatigue endurance of films becomes problematic after cycles with a decrease in remanent polarization to 85% of the original value. This phenomenon was related to electron injection and creation of electron traps due to the occupation of Sr vacancies by Bi cations. It is demonstrated that the fatigue endurance of film can be improved by doping with 20 mol % PbO.
87(2000); http://dx.doi.org/10.1063/1.373492View Description Hide Description
Imaging of the phase and magnitude of the piezoelectric strain in (PZT) capacitors is performed with an atomic force microscope. The imaging reveals a significant spatial dependence of the ferroelectricproperties of both fatigued and unfatigued PZT films. We propose that the variation is related to the domain structure of the PZT. Through the measurement of local piezoelectric hysteresis loops and imaging of the piezoelectric strain, areas are observed in fatigued PZT that exhibit hysteresis loops shifted along the polarization axis. In some regions of fatigued samples, the hysteresis loops are shifted such that both remanent points of the hysteresis curve have the same polarization direction. These results have important implications for the scalability of nonvolatile ferroelectric random access memory to higher device densities.
87(2000); http://dx.doi.org/10.1063/1.373493View Description Hide Description
Strain relaxation and its effect on domain formation of epitaxialthin filmsgrown on MgO (001) substrates were investigated as a function of film thickness by two-dimensional reciprocal space mapping using synchrotron x-ray diffraction. Within a few hundreds of angstrom region, it was observed that c-domain abundance, α, was critically dependent on film thickness. As the film thickness increased further, α was saturated at a value of ∼0.75. The HK mesh scan on (100) reflections revealed that directional tilting of a domains with four-fold symmetry began to develop as the film thickness exceeded 650 Å. Thermodynamic equilibrium relief of the coherency strain was evaluated based on Mattews–Blakslee criteria that determine thickness dependent misfit accommodation. This theoretical consideration with experimental results led us to conclude that the unrelaxed residual misfit strain has a significant effect on the domain formation, particularly in the region below the thickness of 1000 Å.