Volume 94, Issue 6, 15 September 2003
Index of content:
- DIELECTRICS AND FERROELECTRICITY (PACS 77)
94(2003); http://dx.doi.org/10.1063/1.1599977View Description Hide Description
This article presents a simple method for calculating the stress current in accelerated test of time dependent dielectric breakdown of stacked dielectrics. By replacing an energy barrier of arbitrary shape with a series of rectangular energy barriers and resolving rigorously the Schrödinger equation in each regions, interfaces and variations of electron effective masses in different dielectrics have been analyzed. Our calculations fit experimental data well. The method is applicable in this reliability study aimed at failure mechanism detection and prediction.
Influence of Schottky and Poole–Frenkel emission on the retention property of -based metal/ferroelectric/insulator/semiconductor capacitors94(2003); http://dx.doi.org/10.1063/1.1601292View Description Hide Description
The relationship between the memory retention properties and the leakage current density of capacitors was discussed. The leakage current of the ferroelectric layer was varied by temperature and by annealing the capacitors. It was found that the retention time became shorter upon increasing the leakage current density at the retention voltage. The retention time was prolonged from about to up to when the leakage current density was reduced to by annealing under ambient. The analysis of the leakage current revealed that the retention degradation mechanism was related to the Schottky emission. From the temperature dependence of the leakage current and the pseudo isothermal capacitance transient spectrum, it was found that applied voltage with an unnecessarily long time to polarize the ferroelectric layer generated Frenkel defects in the ferroelectric layer, and that the amount of the defects greatly affected the memory retention time. These results suggest that to improve the memory retention properties, reducing the defect density of the ferroelectric layer is important, as well as lowering the Schottky current.
94(2003); http://dx.doi.org/10.1063/1.1596714View Description Hide Description
Ferroelectric and superconductor bilayers of (YBCO) are grown on substrates by magnetronsputtering and pulsed laser deposition. The BST thin films exhibit typical ferroelectric behavior in their hysteresis loops. Capacitance–voltage curves are measured. From the capacitance, a dielectric constant of 1250 is obtained. The current–voltage curve is fitted to investigate the mechanism of leakage. The Schottky barrier height at the Ag/BST interface is calculated to be 0.521 eV. The trapped level in BST is estimated to be 0.335 eV below the conduction-band edge. An energy band diagram of the Ag/BST/YBCO structure is proposed to explain the experimental results.
94(2003); http://dx.doi.org/10.1063/1.1604963View Description Hide Description
Pulsed excimer laser irradiation of an absorbing thin film through a transparent substrate has been employed to separate epitaxial (PLZT) thin films from their MgO growth substrates. The morphology, microstructure, and dielectric properties of the laser-modified PLZT layer generated at the original PLZT/MgO interface by this laser liftoff (LLO) process was investigated. Atomic force microscopy measurements of the filmsurface after LLO indicated average surface roughness on the order of 90–100 nm, complementing previously reported scanning electron microscopy studies that revealed what appeared to be a rough glassy layer. The surface roughness is thought to form as the original growth substrate is ejected from the films transferred towards the end of the 38 ns pulse, pulling the molten near-interfacial portion of the PLZT film via surface tension, and followed by quenching of the liquid phase. Transmission electron microscopy of PLZT films transferred to Si wafers showed the surface layer consists of an irregular amorphous layer ranging in thickness from 50 to 100 nm, although some surface features protruded as far as 300 nm. Enhanced levels of lead were found to be present in the amorphous phase by Rutherford backscattering spectrometry, implying PbO evaporation and subsequent condensation during LLO. Electrical measurements determined the relative dielectric constant of the surface layer to be in the range of 40 – 70. Subsequent ion milling of the layer demonstrated that the ferroelectric and dielectric properties of the original PLZT films were largely recovered, while the surface roughness was reduced to below 40 nm. The observed differences between the dielectric and ferroelectricproperties of the film transferred after complete removal of the amorphous layer compared to those of the film on the original MgO substrate are attributed to the removal of substrate clamping.
94(2003); http://dx.doi.org/10.1063/1.1603345View Description Hide Description
The use of atomic force microscopy(AFM) to tailor and image ferroelectric domains in the submicron and nanometer ranges is gaining increasing attention. Many applications have been developed that make use of the superhigh electric field generated by the sharp AFM tip in a local area. In this article, we derive an explicit expression for the AFM-induced electric field in a ferroelectric thin film. Based on a similar approach, we also obtain the depolarization field created by polarization charges using the Green function technique. Based on the expressions derived, the effects of the substrate are discussed.