In this paper, the resistive switching and neuromorphic behaviour of memristive devices based on parylene, a polymer both low-cost and safe for the human body, is comprehensively studied. The Metal/Parylene/ITO sandwich structures were prepared by means of the standard gas phase surface polymerization method with different top active metal electrodes (Ag, Al, Cu or Ti of ~500 nm thickness). These organic memristive devices exhibit excellent performance: low switching voltage (down to 1 V), large OFF/ON resistance ratio (up to 10 4 ), retention (≥10 4 s) and high multilevel resistance switching (at least 16 stable resistive states in the case of Cu electrodes). We have experimentally shown that parylene-based memristive elements can be trained by a biologically inspired spike-timing-dependent plasticity (STDP) mechanism. The obtained results have been used to implement a simple neuromorphic network model of classical conditioning. The described advantages allow considering parylene-based organic memristors as prospective devices for hardware realization of spiking artificial neuron networks capable of supervised and unsupervised learning and suitable for biomedical applications.

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N-doped nanocrystalline titania microspheres with controlled visible light absorption were obtained by a new route utilizing a heterogeneous hydrolysis of TiCl 4 vapor with reactive droplets of aqueous aerosols, followed by instant calcination of the products in a preheated flow reactor. Thus prepared separate microspheres with a diameter of 0.5-3 microns were found to consist of anatase or rutile nanocrystals, depending on the parameters of the synthesis. Doped titania samples with different nitrogen contents were synthesized using water solutions with various concentrations of urea in the hydrolyzing aerosols. N À species were found to be a major form of nitrogen impurity. A plausible mechanism for the incorporation of nitrogen into titanium dioxide was proposed. The photocatalytic activity of the obtained powders under UV-visible or visible illumination was found to have a complex dependence on the calcination temperature and the titania doping level. ExperimentalThe experimental setup consists of two main parts, the rst for vaporized TiCl 4 hydrolysis with a water-based aerosol, and the

The development of memristor-based spiking neuromorphic systems (NS) has been essentially driven by the hope to replicate the extremely high energy efficiency of biological systems. Spike-timing-dependent plasticity (STDP) mechanism is considered as one of the most promising learning rules for NS. STDP learning has been observed in different types of biological synapses in presence of neuromodulators, e.g. dopamine, and is believed to be an enabling phenomenon for important biological functions such as associative and reinforcement learning. However, the direct STDP window change under dopamine-like modulation has not been yet demonstrated in memristive synapses. In this study, we experimentally demonstrate a simple way for the STDP window shape modulation by introducing the coefficients controlling the neuron spike amplitudes. In such a way the STDP window shape could be modulated from a classical asymmetric shape to a bell-shaped, as well as to anti-STDP and to anti-bell-shaped. The experiments have been carried out with (Co0.4Fe0.4B0.2)x(LiNbO3)1−x nanocomposite-based memristors. Memristive characteristics of the nanocomposite structures with different metal content are also comprehensively studied. Obtained results give every hope for bio-inspired operation of the future large memristor-based NS with reinforcement learning ability.

Resistive and capacitive switching in capacitor metal/nanocomposite/metal structures based on (CoFeB) x (LiNbO 3 ) 100−x nanocomposite (NC) fabricated by ion-beam sputtering with metal content x  8-20 at. % is studied. The peculiarity of the structure synthesis was the use of increased oxygen content ( 210 −5 Torr) at the initial stage of the NC growth. The NC films, along with metal nanogranules of 3-7 nm in size, contained a large number of dispersed Co (Fe) atoms (up to ~10 22 cm -3 ). Measurements were performed both in DC and AC (frequency range 5-13 MHz) regimes. When switching structures from high-resistance (R off ) to low-resistance (R on ) state, the effect of a strong increase in their capacity was found, which reaches 8 times at x  15 at. % and the resistance ratio R off /R on  40. The effect is explained by the synergetic combination of the multifilamentary character of resistive switching and structural features of the samples associated, in particular, with the formation of high-resistance and strongly polarizable LiNbO 3 layer near the bottom electrode of the structures.