T Dimitrova

Elemental composition and structural properties of thin rf sputtered Ta2O5 layers

AES and XPS have been used for investigation of the elemental composition and the chemical bonding in rf sputtered tantalum oxide (4-75 nm) on Si, depending on gas mixture (O 2 content in the gas 0.2-50%) at two substrate temperatures. The effect of post deposition anneal in dry O 2 has also been considered. The results indicate that 10% O 2 content and substrate temperature 300 K favour formation of stoichiometric Ta 2 O 5 and an abrupt interface transition region between Si and Ta 2 O 5 . The annealing leads to homogenization of the layers and improves additionally their stoichiometry.

Interface and oxide properties of rf sputtered Ta2O5- Si structures

Abstract Interface and oxide properties of Ta 2 O 5 -Si structures with rf sputtered Ta 2 O 5 of 7–80 nm thickness have been investigated using capacitors on p-Si and transistor-like test structures. It is found tha the electrical properties of the films are dominated by an extremely thin SiO 2 layer which is unavoidably formed at the interface Si-Ta 2 O 5 during rf sputtering. The as-deposited layers exhibit a large defect density in the form of oxide charges and acceptor type interface states, which are thickness dependent. A high density of interface states in the upper half of the Si band gap is detected. High temperature annealing at 1123 K in oxygen is effective for the reduction of the fixed oxide charges, that are reduced by about two orders of magnitude. The nature of the electrically active centres is proposed to be defects such as weak dangling Ta–O bonds and\or Si–O bonds.

Low-permittivity evaporated polymer-polyimide☆

Abstract The development of modern microelectronics produces a need to develop materials with a relative dielectric constant ϵr, lower than that of silicon dioxide for intermetal applications. Lower permittivities mean lower capacitances and therefore shorter RC delay, faster device speeds, less crosstalk and less power dissipation. A promising “tailor made” candidate is the evaporated polymer-polyimide. The dielectric properties of evaporated polyimide layers (ODA-PMDA) are investigated. Three thicknesses of the layers are used — 1100, 190 and 170 nm. The electrical properties of the layers are evaluated on capacitors of different areas using C-V and l-V measurements. The lowest values of the relative dielectric constant ϵr and the loss-tangent tg δ obtained are 2.67 and 0.0021, respectively.

Late Permian (Tatarian) fluvio-lacustrine successions in NW Anatolia (Zonguldak Terrane, Turkey): palaeogeographic implications

Late Permian fluvio-lacustrine successions of the Cakraz Formation in the Zonguldak Terrane between the regions of Akcakoca and Eregli were investigated in order to describe the litho- and biostratigraphic properties and explain the depositional environment. The studied succession with black, dark-grey to greenish-grey shales, siltstones and limestones is named the Alapli Member to distinguish it from the classical red clastic successions, which are tentatively named the Eregli Member of the Cakraz Formation. The organic-rich black shales, mudstones and limestones of the Alapli Member yielded palynological assemblages suggesting a Lopingian (Tatarian) age. The lack of any marine macro- or microfossils, the fine-grained character of the lithofacies with abundant plant material and the association of poorly sorted conglomerates in the middle part of the succession indicate possible deposition in a broad range of fluvial and lacustrine environments. Successions of similar age and depositional environment are known from the East European Variscan Belt in Bulgaria and Romania. Common successions were also developed in actively extending shallow-marine platforms on the NW Palaeotethyan margin at the end of the Permian Period.