Retentivity of RRAM Devices Based on Metal / YBCO Interfaces

ABSTRACTThe retention time of the resistive state is a key parameter that characterizes the possible utilization of the RRAM devices as a non – volatile memory device. The understanding of the mechanism of the time relaxation process of the information state may be essential to improve their performances. In this study we examine RRAM devices based on metal / YBCO interfaces in order to comprehend the physics beneath the resistive switching phenomenon.Our experimental results show that after producing the switching of the resistance from a low to a high state, or vice versa, the resistance evolves to its previous state in a small but noticeable percentage. We have measured long relaxation effects on the resistance state of devices composed by metal (Au, Pt) / ceramic YBCO interfaces in the temperature range 77 K – 300 K. This time relaxation can be described by a stretched exponential law that is characterized by a power exponent n = 0.5, which is temperature independent, and by a relaxation time τ that increases with increasing the temperature. These characteristics point out to a non-thermally assisted diffusion process that could be associated with oxygen (or vacancy) migration and that produces the growth of a conducting (or insulating) fractal structure.

Effect of Specific Surface Area on Growth and Porosity of Oxide Superconducting Ceramic YBCO Single Domain

The effect of specific surface area on the growth and the porosity of oxide ceramic superconductor YBCO single domain are investigated. The enhancement of growth depth depends on the large specific surface area σ. When the specific surface area σ is more than the critical value 200mm2/g, the YBCO single domain is full-growth in the sample of size Ф20mm×18mm. It reveals that a large specific surface area providing an effective tunnel of oxygen diffusion for the crystal growth. On the other hand, this tunnel makes oxygen gas emitting out resulting in porosity diameter decreased. The mean porosity diameter is observed as 5μm in hole sample smaller than 80μm in plain sample. The porosity distribution is calculated as 1/(100μm)2 in plain sample and 8/(10μm)2 in hole sample.

Degradation of YBC critical current as a result of annealing in air

The present study was aimed at determining the rate of degradation of the transport critical current density Jc of ceramic YBCO stored in atmosphere, as a function of temperature. The transport critical current of ring-shaped samples was measured by the inductance technique. The samples were prepared by the standard method. The results show that annealing at 100 °C for over 500 h caused practically no degradation of Jc. Above 100 °C the rate of degradation increases rapidly with temperature.