  In this paper, the resistive switching and neuromorphic behavior 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 about 500 nm thickness). These organic memristive devices exhibit
excellent performance: low switching voltage (down to 1 V), large OFF/ON
resistance ratio (about 10^3), 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.
