A new type of memory device that will allow for much greater miniaturization and efficiency than current RAM has proved to have a surprising property. German researchers reported in a recent issue of Nature Communications that ReRAM (resistive memory cells) has a battery-type effect in which the devices actually store charge. This helps explain some anomalous behavior in memristors, the class of circuit elements that subsumes ReRAM.
Resistive memory cells (ReRAM or RRAM) have the potential to become a front-runner technology among nonvolatile memories. First developed by HP in 2008, ReRAM exhibits fast switching times and is suitable for low-power applications, because it requires less voltage. ReRAM differs from conventional computer memory by using ions (charged atoms) for storing data, rather than electrons, which owing to their tinier size are harder to control, impacting both data storage density and energy use.
The new research study reports that the ions in ReRAM behave like a battery. The data storage function in ReRAM is realized by the movement of ions between the memory cell’s two electrodes, silver or copper on the active end, and platinum, for example, on the inert end. A positive voltage leads to metal depositing at the counter electrode, which eventually forms a filament that short circuits the cell by connecting the two ends. This corresponds to the cell’s “on” state, while the “off” state can be restored by applying an oppositely polarized voltage.
A byproduct of this switching is the generation of an electric voltage, meaning the ReRAM cells act like tiny batteries. This finding has an impact not just for potentially improving data readout (an idea that the research team has patented), but also has theoretical implications. ReRAM, with active electrochemical components, violates the definition of memristors as passive circuit elements. The researchers argue that their finding means the memristor concept needs to be expanded, and that ReRAM cells are real memristors, something memristor pioneer Leon Chua has also argued.
Image via Jülich Aachen Research Alliance