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IBM reveals ionic currents charge memory chips

26 Mar 2013

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A breakthrough in materials science has been announced by IBM recently. Logic and non-volatile memory (NVM) chips may be able to use less power through the use of ionic currents in operating semiconducting devices, as these tiny streams of charged atoms mimic the event-driven way that the human brain operates.

IBM research scientists showed that it is possible to reversibly transform metal oxides between insulating and conductive states by the insertion and removal of oxygen ions driven by electric fields at oxide-liquid interfaces. Once the oxide materials, which are innately insulating, are transformed into a conducting state, the IBM experiments showed that the materials maintain a stable metallic state even when power to the device is removed. This non-volatile property means that chips using devices that operate using this novel phenomenon could be used to store and transport data in a more efficient, event-driven manner instead of requiring the state of the devices to be maintained by constant electrical currents.

"Our ability to understand and control matter at atomic scale dimensions allows us to engineer new materials and devices that operate on entirely different principles than the silicon based information technologies of today," said Dr. Stuart Parkin , an IBM Fellow at IBM Research. "Going beyond today's charge-based devices to those that use miniscule ionic currents to reversibly control the state of matter has the potential for new types of mobile devices. Using these devices and concepts in novel three-dimensional architectures could prevent the information technology industry from hitting a technology brick wall."

Ionic current powered memory chips

The figure shows a schematic of a nanofluidic circuit that operates by passing ionic fluid (green) through conduits fabricated on top of a planar oxide surface (orange). A voltage is applied to the liquid (blue gate) which results in the electric field induced motion of oxygen ions (yellow balls) from the oxide surface into the liquid. This results in the metallization of the oxide (redder region) beneath the liquid that is subject to the gate voltage. Where no voltage is applied (pale blue gate) there is no ionic motion and the oxide surface remains insulating. Thus circuits can be dynamically formed in the surface of the oxide. Reverse gating results in the reverse motion of oxygen and the oxide returns to its insulating state.

The process
To achieve this breakthrough, IBM researchers applied a positively charged ionic liquid electrolyte to an insulating oxide material—vanadium dioxide—and successfully converted the material to a metallic state. The material held its metallic state until a negatively charged ionic liquid electrolyte was applied, to convert it back to its original, insulating state.

Such metal to insulator transition materials have been extensively researched for a number of years. However, contrary to earlier conclusions, IBM discovered that it is the removal and injection of oxygen into the metal oxides that is responsible for the changes in state of the oxide material when subjected to intense electric fields.

The transition from a conducting state to an insulating state has also previously been obtained by changing the temperature or applying an external stress, both of which do not lend themselves to device applications.

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