Researchers from the University of Michigan have discovered the role of phase separation in memristor mechanism, thus paving the way to improving RRAM memory.
Up until now, researchers were not sure why memristors retain their memory for a long time, as current models did not explain this fully. The new researchers explain that in memristors, oxygen ions prefer to be away from the filament and will never diffuse back, even after an indefinite period of time.
The researchers performed the sutdy using an RRAM device, in which a filament-type valence change memory (VCM), sandwiches an insulating tantalum oxide layer between two platinum electrodes. Using the extremely high-resolution imaging of atomic force microscopy, the researchers imaged filaments, which measure only about five nanometers or 20 atoms wide, forming within the one micron wide RRAM device. The research team found that different sized filaments yielded different retention behavior. Filaments smaller than about 5 nanometers dissolved over time, whereas filaments larger than 5 nanometers strengthened over time. The size-based difference cannot be explained by diffusion alone. Together, experimental results and models incorporating thermodynamic principles showed the formation and stability of conductive filaments depend on phase separation.