TiO2 based memristive devices towards controlling performances and interfacing

Abstract

The main aims of this thesis are to evaluate suitability of TiO2 thin films, synthesized by Pulsed Microplasma Cluster Source (PMCS), for realization of devices showing memristive response and that could be used in a neuron-memristor hybrid system, where biological system and electronics could interact each other. All research activities have been carried out at the IMEM-CNR laboratories of Trento, in the mainframe of a four-year project named Madelena where different partners are involved, with skills from materials science to electronics and biology. The PMCS deposition technique uses supersonic molecular pulsed beams seeded by clusters of the metal oxide synthesized in a plasma discharge. In order to achieve the film properties necessary for electronic applications, by a tough optimization of the deposition process it has been possible to synthesize TiO2 thin films having suitable, controlled and reproducible properties. In general, all PMCS thin films showed an anatase TiO2 structure, grain dimension size lower than 20nm, an average roughness of about 3nm and with the possibility to control oxygen stoichiometry, with a O/Ti ratio from 2 to 2.2 by changing the composition of the used gas carrier. The inedited employing of the PMCS in memristive application showed promising results. Indeed, using as top electrode a Pt wire, all the PMCS TiO2 have exhibited a significant memristive response, modulated by the intrinsic chemistry of the material. In particular by increasing of the percentage of oxygen in the matrix, both resistances (ON state and OFF state) and the voltage switch increases. Moreover, a MIM device has been realized showing same main electrical properties, with device life as long as 1000 cycles. To achieve the proposed challenging final aims, an important study has been carried on the biocompatibility and neurocompatibility of TiO2 grown by PMCS. All the films guaranteed consistent biocompatibility and a spontaneous absorption of poly-D-lysine (PDL) that has increased their neurocompatibility. Moreover, the electrical activities of the neural culture grown on the TiO2 film can be modulated by changing of the surface chemistry. Finally, starting with these significant and promising results, a prototype of PMCS TIO2 based on memristor-neuron hybrid system was designed and realized, opening new perspectives for the realization of more complex bio-inspired devices.