Electro-forming - the initial step to resistance switching in vacancy-doped metal-SrTiO3-metal structures

Strontium titanate is a widely-used model oxide for solids which crystallize in the perovskite-type of structure. With its large bandgap energy, high dielectric constant and its mixed ionic and electronic conductivity, SrTiO3 is a candidate material for future metal-insulator-metal (MIM) structures in resistive switching memory cells. Here, strontium titanate single crystals doped with oxygen vacancies induced by high temperature vacuum annealing were used. The essential step to enable resistive switching is the electro-forming of the structures by dedicated current-voltage programs. Therefore, the longtime current behaviour of such MIM stacks was investigated. A degradation of the electrical resistance led to a minimum resistivity after a characteristic forming time. During continued formation the resistivity increases up to a failure of the system. A model related to oxygen vacancy diffusion and the introduction of novel structural phases near the surface is proposed.