Defect state D (0.8 eV) was experimentally detected in Ta2O5 capacitors with ultrathin (physical thickness <10 nm) Ta2O5 films using zero-bias thermally stimulated current spectroscopy and correlated with leakage current. Defect state D can be more efficiently suppressed by using N2O rapid thermal annealing (RTA) instead of using O2 RTA for postdeposition annealing and by using TiN instead of Al for top electrode. We believe that defect D is probably the first ionization level of the oxygen vacancy deep double donor. Other important defects are Si/O-vacancy complex single donors and C/O-vacancy complex single donors.
Defect states responsible for leakage current in ultrathin (physical thickness <10 nm) tantalum pentoxide (Ta2O5) films were measured with a novel zero-bias thermally stimulated current technique. It was found that defect states A, whose activation energy was estimated to be about 0.2 eV, can be more efficiently suppressed by using N2O rapid thermal annealing (RTA) instead of using O2 RTA for postdeposition annealing. The leakage current was also smaller for samples with N2O RTA than those with O2 RTA for postdeposition annealing. Hence, defect states A are quite likely to be important in causing leakage current.
Scanmng tunneling microscopy (STM) images of a self-assembled alkanethiol monolayer film on gold show a structure that contains flat areas with pits. An important characteristic of these pits, and one which has been a subject of interest in the recent literature, is their depth. For instances in which the measured depth is comparable to a single atomic step height of the gold substrate, the pits have been assigned as monolayer-deep defects in the gold substrate, covered by alkanethiol molecules. For instances in which the measured depth is greater than a single atomic step height ofgold, the pita have been assigned as defects in the alkanethiol monolayer itself. Since the diameters of those pits are small and the tips used for " h g probe microscopy (SPM) imaging have a finite radius, it is possible that the structural interaction between the tip and surface prevents SPM from measuring the true depth of the pits in most cases. In this study, we construct a model to understand this phenomenon quantitatively, and analyze the measured depth of the pita. STM images of self-assembled octadecanethioVAu(ll1) from the same surface but obtained with tips of Merent sizes are presented. We show that in some STM images the apparent depth of the pits is coincidently comparable with the single atomic step height of the gold substrate surface. In other images we show that the true depth of the pit is measured, and that it is interpreted as the thickness of an odadecanethiol monolayer (-25.3 f 0.5 A).
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