Fanni Misják

Electron scattering mechanisms in Cu-Mn films for interconnect applications

Electrical properties and corresponding structural features of Cu-Mn alloy films with potential application as barrier and interconnect layers were studied. Cu-Mn films were deposited by DC magnetron sputtering at room temperature on SiO2 substrates. Electrical resistivity measurements were made as a function of film composition and temperature. The specific resistivity varies linearly with the Mn content showing a maximum of 205 μΩcm at 80 at. % Mn. The temperature coefficient of resistance (TCR) of all alloy films is low, showing non-metallic conductivity for most compositions. Also a minimum TCR has been observed in the 40–80 at. % Mn range which was attributed to a magnetic transformation around 200–300 K. Electrical resistivity measurements are correlated with the film structure revealed by transmission electron microscopy to clarify the phase regions throughout the composition range. In the 20–40 at. % and 70–80 at. % Mn ranges, two-phase structures were identified, where Cu- or Mn-rich solid solution grains were surrounded by a thin amorphous covering layer. Based on the revealed phase regions and morphologies electron scattering mechanisms in the system were evaluated by combining the Matthiessens rule and the Mayadas-Schatzkes theory. Grain boundary reflectivity coefficients (r = 0.6–0.8) were calculated from fitting the model to the measurements. The proposed model indicates that, in a binary system, the special arrangement of the two phases results in new scattering mechanisms. The results are of value in optimizing the various parameters needed to produce a suitable barrier layer.

Episodic Memory and Cognitive Map in a Rate Model Network of the Rat Hippocampus

The hippocampus of rodents seems to play a central role in navigation: place cells are prone to serve as elements of a cognitive map. The hippocampus of primates is apparently involved in episodic memory processes. Here we show how the hippocampi of different species (with their anatomy and physiology being considerably similar) can fulfill both purposes. A network was built from simple rate neurons, synaptic weights were modified by a batch version of the coincidence-based Bienenstock-Cooper-Munro learning rule. The network was trained with temporally contiguous sensory stimuli, and then tested in two different paradigms: (1) for navigational performance, place field profiles were evaluated to allow comparison with experimental data; (2) for memory performance, associative capability was assessed. The same neuron network was found to be able to show place cell properties and function as episodic memory, even when trained with non-topographical stimuli.

Spinodal Decomposition in Nanoparticles - Experiments and Simulation

For revealing internal atomic processes in bimetallic nanoparticles, individual hemispherical Ag-Cu alloy particles were grown by direct current (DC) magnetron sputtering. Phase separation of particles was found to be size- and composition-dependent. Particles smaller than 5 nm in diameter remained as a solid solution of the components for all tested compositions (15-80 at.% Ag). At 15 and 30 at.% Ag compositions phase separation was observed only for particles above 5 nm in diameter. Computer simulations by Stochastic Kinetic Mean Field model reproduced the size-dependence of the decomposition and the internal structure of two-phase particles. Theoretical explanation is given for the composition dependence of the phase separation tendency.

Formation of ordered solid solution during phase separation in Cu-Ag alloy films

The Cu-Ag binary system belongs to the two component systems of practically non mixing components at thermodynamic equilibrium. At non equilibrium conditions however, substantial mixing could be observed. Cu-Ag thin films prepared by vapour [1] or DC sputter [2–4] deposition show solubility of both components (approx. 10 at.%) in each other as observed by XRD measurements. Besides of enhanced solubility formation of hexagonal (hcp) domains was also observed [4]. These results make probable the formation of metastable (ordered solid solution) phases in this system.

Development of texture and morphology in Cu-Ag thin nanocomposite films on Si

Cu-Ag films were deposited in vacuum of 10−5−10−6 mbar onto freshly cleaned Si wafers. The composition of the films corresponded to Cu, Cu9Ag1, Cu4Ag6 and Ag. The films were investigated by X-ray diffraction and pole figures of and directions were recorded. TEM and XTEM were used to determine the morphological properties of the films. We found that Ag modifies the interaction of Cu with the Si substrate. Low amounts of Ag are enhancing the formation of the biaxial texture of Cu. Larger amounts of Ag result in the formation of wire texture of both Ag and Cu components.