Memristors in silicon promising for dense, fast memory

The first purely silicon oxide-based ‘Resistive RAM’ memory chip that can operate in ambient conditions – opening up the possibility of new super-fast memory – has been developed by researchers at UCL (University College of London)

Our ReRAM memory chips need just a thousandth of the energy and are around a hundred times faster than standard Flash memory chips. The fact that the device can operate in ambient conditions and has a continuously variable resistance opens up a huge range of potential applications.

“The potential for this material is huge. During proof of concept development we have shown we can programme the chips using the cycle between two or more states of conductivity. We’re very excited that our devices may be an important step towards new silicon memory chips”

BBC News – Researchers have revealed details of a promising way to make a fundamentally different kind of computer memory chip.

The device is a “memristor”, a long-hypothesised but only recently demonstrated electronic component.

A memristor’s electronic properties make it suitable for both for computing and for far faster, denser memory.

Researchers at the European Materials Research Society meeting now say it can be made much more cheaply, using current semiconductor techniques.

These are the first purely silicon oxide-based ‘Resistive RAM’ memory chip that can operate in ambient conditions – opening up the possibility of new super-fast memory – has been developed by researchers at UCL.

Resistive RAM (or ‘ReRAM’) memory chips are based on materials, most often oxides of metals, whose electrical resistance changes when a voltage is applied – and they “remember” this change even when the power is turned off.

ReRAM chips promise significantly greater memory storage than current technology, such as the Flash memory used on USB sticks, and require much less energy and space.

The researchers are already collaborating with a manufacturer on prototypes

Journal of Applied Physics – Resistive switching in silicon suboxide films

The energy required to switch the state of their devices – the energy it would take to store or retrieve a bit of information – is just a hundredth of that in existing flash memory, and significantly faster.

“Flash memory devices switch at 10,000 nanoseconds (billionths of a second) or so, and in our device we can’t measure how fast it is,” Dr Kenyon said.

“Our equipment only goes down to 90 nanoseconds. It’s at least as fast as that and probably faster.”

Though the team’s idea is a bit behind other more well developed memristor recipes, Dr Kenyon is hopeful the cheap and simple nature of their devices will make them industrially attractive.

We report a study of resistive switching in a silicon-based memristor/resistive RAM (RRAM) device in which the active layer is silicon-rich silica. The resistive switching phenomenon is an intrinsic property of the silicon-rich oxide layer and does not depend on the diffusion of metallic ions to form conductive paths. In contrast to other work in the literature, switching occurs in ambient conditions, and is not limited to the surface of the active material. We propose a switching mechanism driven by competing field-driven formation and current-driven destruction of filamentary conductive pathways. We demonstrate that conduction is dominated by trap assisted tunneling through noncontinuous conduction paths consisting of silicon nanoinclusions in a highly nonstoichiometric suboxide phase. We hypothesize that such nanoinclusions nucleate preferentially at internal grain boundaries in nanostructured films. Switching exhibits the pinched hysteresis I/V loop characteristic of memristive systems, and on/off resistance ratios of 104:1 or higher can be easily achieved. Scanning tunneling microscopy suggests that switchable conductive pathways are 10 nm in diameter or smaller. Programming currents can be as low as 2 μA, and transition times are on the nanosecond scale.

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