Synaptic-like conductivity and plasticity in epitaxially strained SrTiO3 films

Abstract

In this work, we use epitaxial strain and an asymmetric electrode design to engineer the conductivity of SrTiO3 thin films in order to use them as active components in planar artificial synaptic devices. First, the tensile strain imposed by the rare-earth scandate substrate on epitaxial grown SrTiO3 films results in a significant increase of the conductivity of the SrTiO3. Second, a further enhancement of the conductivity is obtained by the use of Ti/Pt electrodes. Finally, the asymmetric electrode design consisting of a flat and a tapered electrode ensures the asymmetric response and plasticity of electronic synapse. The modifications of the conductivity are explained in terms of changes in the density and mobility of oxygen vacancies. The resulting electronic synapses (e-synapse) show memristor behavior and the plasticity of the signal, which are both essential characteristics of a synapse. Similar to the synaptic long-term and short-term potentiation/depression, our SrTiO3 e-synapses show two different types of plasticity, a fast process associated with the ionic dipole formation (relaxation time in the 100 ps regime) and a slow process defined by the mobility of oxygen vacancies (relaxation time of several seconds).