Unsupervised Learning by Spike Timing Dependent Plasticity in Phase Change Memory (PCM) Synapses

We present a novel one-transistor/one-resistor (1T1R) synapse for neuromorphic networks, based on phase change memory (PCM) technology. The synapse is capable of spike-timing dependent plasticity (STDP), where gradual potentiation relies on set transition, namely crystallization, in the PCM, while depression is achieved via reset or amorphization of a chalcogenide active volume. STDP characteristics are demonstrated by experiments under variable initial conditions and number of pulses. Finally, we support the applicability of the 1T1R synapse for learning and recognition of visual patterns by simulations of fully connected neuromorphic networks with 2 or 3 layers with high recognition efficiency. The proposed scheme provides a feasible low-power solution for on-line unsupervised machine learning in smart reconfigurable sensors

Reversing a potential polarity for reading phase change cells to shorten a recovery delay after programming

A potential supplied to selected cells in a Phase Change Memory (PCM) is reversed in polarity following a program operation to suppress a recovery time and provide device stabilization for a read operation

Anomalous cells with low resistance in phase change memory arrays

Resistance distributions for the reset state in phase-change-memory arrays are studied as a function of the programming conditions. The statistical distribution displays a low-resistance tail, which may potentially affect the resistance window between the two states in thememory device. Themajority of tail cells are found to result from the statistical dispersion of the quenching properties of the chalcogenide material and can be corrected by optimizing the programming operation. On the other hand, a residual tail is found, which is characterized in terms of programming, switching, and conducting characteristics. The measured behavior is consistent with extrinsic low-resistance paths in the programmable volume, which shunts the highresistance amorphous phase and prevents reaching a fully reset resistance. Removal of this extrinsic tail in the reset distribution is demonstrated by careful optimization of the integration process

Resonant valence-band photoemission spectroscopy on the Fe62Ni20Cr18 alloy

The Fe62Ni20Cr18 valence band was studied by scanning the photon energy across the 2p3/2 core-level threshold of each element of the alloy. A resonant enhancement of the weak 3d-like features was observed. In pure transition metals, similar valence band resonances are explained by a radiation-less Raman de-excitation emission, which is active at threshold and degenerate with the two-hole satellite of direct photoemission. Present structures are associated to satellite features occurring in Fe62Ni20Cr18, and their intensities and binding energies are compared to those of the pure metal components. The alloy satellite resonant behaviour reveals some peculiar modifications of: a) the crossover between the radiation-less Raman scattering and the Auger emission regimes; b) the ratio of the relative intensities of the main and satellite peaks. We mainly assign these differences to the hetero-nuclear bonds in the alloy. Copyright EDP Sciences/Società Italiana di Fisica/Springer-Verlag 2005

The Au(I) Catalyzed Activation of Allenamides and Their Subsequent Transformation into Chromanes: A Method for the Regiocontrolled Addition to the α- and γ-Positions of the Allene Unit

This definitive published version of this article is available from: http://dx.doi.org/10.1021/ol502178vAu(I) activation of allenamides in the presence of phenols leads to the formation of chromanes in moderate to good yields. This catalytic process is dependent on the counterion which facilitates the activation of the in situ formed imine. Furthermore, this iminium can be intercepted by trimethylallyl silane, via the Hosomi–Sakurai reaction, giving a formal procedure for the regioselective intermolecular addition of two carbon nucleophiles to an allenamide at the α- and γ-positions