Volume 92, Issue 2, 15 July 2002
Index of content:
- DIELECTRICS AND FERROELECTRICITY (PACS 77)
92(2002); http://dx.doi.org/10.1063/1.1483916View Description Hide Description
Low-kfilms with k of 2.5–2.9 were deposited under different conditions of pressures and temperatures using a plasma-enhanced chemical vapor deposition(PECVD) system. These films were prepared using a new liquid precursor, tetravinyltetramethylcyclotetrasiloxane (TVTMCTS) and carrier gas. The rf power was kept as low as possible to maintain the original ring structure in the films. The as-deposited films were annealed and the dielectric and optical properties were investigated. Identification of the absorption bands in the IR spectra for as-deposited films reveals a broadband around 950–1200 arising from the Si–O stretching mode of the ring (1065 and chain structure (1000 respectively; a band at 750–900 due to Si–O bending (790 rocking mode (760 a sharp band centered at 1260 due to a bending mode; and a broadband at 2800–3000 due to the CH group. A comparison of the IR spectra of the PECVDfilm and TVTMCTS liquid reveals that vinyl vibrations at 960, 1410, and 3030–3095 for and at 1598 for C=C present in the liquid were not detected in the CVDfilms. Hence C=C bonds were broken in the plasma polymerization process. As the pressure and the depositiontemperature increased, the intensity of the Si–O vibration arising from the ring structure increased and decreased, respectively. Thus by tuning the pressure and we can control the structure of the film. There is a good correlation found between the and Si–O ring intensities and k values; the increasing and Si–O ring is accompanied by decreasing k. The films were thermally stable up to annealingtemperature.
92(2002); http://dx.doi.org/10.1063/1.1486049View Description Hide Description
The behavior of the bulk electrical resistivity of donor-doped with the increase of donor concentration was investigated. A series of coarse-grained specimens with different donor concentrations were prepared by adjusting the oxygen partial pressure during sintering. Then they were heat treated in air for an extended period in order to reach the equilibrium defect distribution corresponding to each heating temperature, which was followed by fast cooling. The critical donor concentrations, beyond which the bulk resistivity increases abruptly, were experimentally evaluated and they were found to decrease with a decrease in the equilibrium temperature in air. Each defect and electron concentrations as a function of donor concentration were theoretically calculated based on the model that the resistivity anomaly is caused by the partially ionized cation vacancies at high temperature, which trap electrons, and become fully ionized cation vacancies as specimens are cooled to room temperature. The results calculated could explain the experimentally observed behavior of the bulk resistivity versus donor concentration.
Ion beam etching of lead–zirconate–titanate thin films: Correlation between etching parameters and electrical properties evolution92(2002); http://dx.doi.org/10.1063/1.1476970View Description Hide Description
Ion beametching of sputtered(PZT) with x equal to 0.54 thin filmsgrown on substrates has been performed using pure Ar gas. The etch rate dependence on the process parameters (current density, acceleration voltage, gas pressure) has been investigated. The PZTetch rate can reach 600 Å/min with acceleration voltage of 1000 V and current density of Selectivity ratios between PZT and masks of various natures (photoresist, Pt, Ti) have been evaluated to determine a pertinent material for etching mask. According to our etching conditions, titanium seems to be the best candidate. We evaluated the PZT surface damage by contact mode atomic force microscopy. It appears that the roughness increases after ion bombardment, and that the grain boundary zone is preferentially etched. For some etching parameters, we also observed electrical damage. Carrying out and hysteresis loops measurements before and after etching have provided evidence of degradation. We noted a large decrease in permittivity after the etching process irrespective of the current density and acceleration voltage. Ferroelectric damage was illustrated by a large increase in the average coercive field. For each of the electrical properties under study, the same behavior has been observed after etching: the increase of damage was obtained as a function of the current density and acceleration voltage. The evolution of electrical properties when the PZT layer is protected by a metallic mask has also been studied. We observed very slight variations in the electrical properties.
92(2002); http://dx.doi.org/10.1063/1.1486031View Description Hide Description
The ferroelectricproperties of thin filmsgrown by laser ablation were investigated as a function of the content in the films. Different target compositions were used to obtain films with different ratios. The initial composition was according to the stoichiometric composition (1/2), and the ratio was varied to 0.7/2.0. It was seen that the remanent polarization showed a consistent increase, as the film became more deficient of up to a certain extent. Similarly, a decrease in the dielectric constant and the leakage current with the decrease of in the film was observed. The dielectric transition temperature showed an increase with the reduction of content and was seen to approach the bulk value.