Resistive Switching And Brain Function Emulation With Memristors Based On Transition Metal Oxides

The rapid development in the artificial intelligence aims to construct brain-inspired computers.The complicated biological abilities of human brain rely on the complicated and gigantic neural network composed of neurons and synapses that can process and store information in parallel.The memristor based on resistive switching phenomena,which behaves like a biological synapse or neuron,present great potentials for the hardware implementation of the artificial neural network and further the realization of the artificial intelligence.However,lots of studies still remain from the point of view of materials science:?1?Resistive switching phenomena exist in various materials system and the detailed mechanisms are still in controversy;?2?Developments of memristor which exhibits higher similarities to biological synapses in both functionality and dynamics are still lacking.We investigated two typical transition metal oxides,TiO₂ and SrTiO₃;the major results are as follows:TiO₂ is the typical switching dielectric in binary oxides.TiO₂ thin films were prepared on Ti foils by the electrochemical anodization of Ti foils,and the resistive switching behaviors of Pt/TiO₂/Ti devices were investigated.Bipolar switching with opposite polarities?namely "anti-clockwise" and "clockwise"?was discovered in the same device,different from the usual coexistence of unipolar and bipolar switching in TiO₂ films.The intermediate transition process was captured to understand the switching mechanism of the anodic TiO₂ film.An electron/ion co-dominating effect was proposed to explain the anomalous phenomenon.SrTiO₃ is the typical switching material in ternary oxides.Taking the advantage of the well-established defect chemistry of SrTiO₃,acceptor and donor doped SrTiO₃ films and single crystals are used as model systems to understand the roles of oxygen vacancies and the Schottky barrier in the resistive switching.Nb doped SrTiO₃ was used to evaluate the role of the Schottky barrier.A direct relationship between the resistance state and the Schottky barrier height was established.Acceptor doped SrTiO₃ films were prepared by pulsed laser deposition technique?PLD?.The effects of the deposition parameters and substrate on the crystal structure and morphology were investigated.The effects of electrode composition and electroforming methods on resistive switching were also studied.Meanwhile,SrTiO₃ based memristive devices were used to emulate the neurological and psychological functions of the brain.The neurological synaptic plasticity was achieved with Ni/Nb-SrTiO₃/Ti memristive devices.Pavlovian conditioning,a classical learning case of the brain,was systematically demonstrated.The learning and forgetting processes of the brain,together with the resultant explicit and implicit memories,were also realized with the device.The electric responses of the memristive devices embody the "time-saving" effect of the implicit memory.The emulation of various neurological and psychological functions in a single memristive device simplifies the construction of the artificial neural network and offers more possibilities for the brain-inspired functionality.