ELECTRONICS : Switching mechanism

Memristive or so-called ReRAM memories are regarded as the storage devices of the future. They are extremely fast and energy-saving - and the stored information is maintained even after a power failure.

View into the photoemission microscope: On switching, the oxygen concentration of the active layer changes.
Photo: Research Center Jülich / Regine Panknin

However, they have not known exactly how they work. Researchers from Aachen, Jülich and Grenoble have now jointly deciphered this with the help of an electron microscope.

In principle, the memory process in the case of memreric cells is successful because their electrical resistance is not constant.  By applying a voltage it can be changed and reset. For example, a low resistance represents the logical "1" and a higher represents the "0". In this way, practically every information can be stored in a binary code. 

However, the technology has not yet matured in order to displace the current storage types. As the origin of the switching, chemical reactions on the nanoscale are assumed, but they could not prove experimentally. And without proper knowledge of these processes, the memories can not be used optimally. 

"Up to now, it was thought that during the switching process, oxygen vacancies migrate in the oxide layer," says Regina Dittmann of Forschungszentrum Jülich (FZJ). "But this could not explain the switching in our cells." Therefore, they examined them in a transmission electron microscope. Special procedures can also be used to examine small changes in the chemical and electronic structure with atomic resolution.

"This is how we discovered that during switching, the total oxygen concentration in the so-called active layer changes," says Dittmann. "By applying electrical voltage, an electrocatalysis is thus set in motion, which ensures that oxygen is constantly installed and removed in the oxide layer between the two electrodes." Together with the long-expected redistribution of the vacancies, the resistance of the device changes.

The researchers hope to be able to adjust the properties of future components more specifically. As a result, significantly higher changes in the resistance could be achieved, which should facilitate the integration of the cells into complex chips.

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