University College London

Researchers at University College London (UCL) have developed the first purely silicon-oxide-based resistive RAM chip that can operate under ambient conditions. The new design opens the possibility of creating superfast memory that doesn’t lose stored data when power is turned off.

The most-often-used materials for resistive RAM (ReRAM) chips are metal oxides whose electrical resistance changes when a voltage is applied. But unlike other electrical properties that vanish when power is turned off, the resistance change of these materials remains even after power is removed. ReRAM chips need much less energy and space than current Flash memory used in USB sticks, so they could be used for low-powered fast memory with greater storage capacity.

The novel structure developed by the research team is made from silicon oxide. The silicon atoms change to form less-resistive filaments within the silicon-oxide material. The presence or absence of these filaments represents a switch from one state to another.

Until recently, other silicon oxide ReRAM chips needed a vacuum to work, thus limiting their usefulness. The new chips have no such limitation. This approach also raises the possibility of transparent memory chips for use in touchscreens and mobile devices.

Dr. Tony Kenyon, a leader of the UCL Electronic and Electrical Engineering team and Fellow of the Institute of Physics, states, “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 they can operate in ambient conditions and have a continuously variable resistance opens up a huge range of potential applications.”

The continuously variable resistance depends on the last voltage applied. This lets the device mimic how neurons in the brain function. Devices that operate in this way are known as memristors.

Earlier memristors were based on titanium dioxide. The development of a silicon-oxide memristor offers greater potential for incorporation into silicon chips.

The new ReRAM technology was discovered by accident while engineers at UCL were testing silicon oxide in the production of silicon-based LEDs. Researchers noticed that the devices appeared to be unstable. UCL Ph.D. student Adnan Mehonic discovered that the material wasn’t unstable, but predictably flipped between various conducting and nonconducting states.

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