In a phase change memory the device resistance corresponding to the amorphous phase monotonically increases with time after the reset programming operation. This phenomenon, called drift, affects the stability of the high resistive state, namely the reset state. In this work we investigate the resistance-drift process through ellipsometric measurements as a function of time in thin film of as-deposited amorphous Ge2Sb2Te5 alloy. We show a tight correlation between the resistance increase with time and the optical band gap widening extracted by ellipsometric measurements. This characterization supports the drift origin due to a structural atomic rearrangement of the amorphous network affecting the band structure that, in particular, promotes the increase of the energy gap and the reduction of localized states within the energy gap.
Structural and morphological studies were carried out on cerium-and gadolinium-doped sol-gel silica glasses intended for scintillator applications, to deepen the understanding of rare earth ion incorporation into the glass matrix. Several compositions, ranging from 0 to 5 mol % Ce and from 0 to 8 mol % Gd, were studied by Raman spectroscopy. The vibrational response was compared to that of pure silica glasses: for cerium doping higher than 0.5 mol %, the F 2g Raman mode, characteristic of CeO 2 , was observed. The presence of CeO 2 nanocrystalline clusters, whose size depends on cerium concentration and thermal treatment, was confirmed also by X-ray powder diffraction (XRD) patterns and transmission electron microscopy (TEM) analyses. On the contrary, gadolinium-doped sol-gel silica glasses exhibited Raman spectra similar to those of pure silica glasses, at least for the investigated concentrations up to 8 mol %, and no crystalline particles were detected within the amorphous matrix.
As the detection of inorganic contaminants is of steadily increasing importance for the improvement of yields in microelectronic applications, the aim of one of the joint research activity within the European Integrated Activity of Excellence and Networking for Nano- and Micro-Electronics Analysis (ANNA, site: www.ANNA-i3.org) is the development and assessment of new methodolo¬gies and metrologies for the detection of low concentration inorganic contaminants in silicon and in novel materials. A main objective consist in the benchmarking of various analytical techniques avail¬able in the laboratories of the participating ANNA partners, including the improvement of the res¬pective detection limits as well as the quantitation reliablity of selected analytical techniques such as total-reflection x-ray fluorescence (TXRF) analysis.
In this paper, we test proximity gettering layers obtained by carbon or silicon implantation for their efficiency in molybdenum and tungsten gettering. DLTS was used to measure the impurity concentration in the solid solution and so to evaluate gettering efficiency. It was found that carbon implantation is effective in capturing these impurities, whereas silicon implantation is not. Extended defects seem not to play an important role in gettering these impurities. In addition, gettering was found to be most effective at high impurity concentration.
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