Ambient-savvy silicon oxide-based Resistive RAM memory chip

Researchers from the University College London (UCL) managed to construct the first purely silicon oxide-based ‘Resistive RAM’ (ReRAM) memory chip that can operate in ambient conditions. ReRAM chips promise far greater speed than currently available memory technologies, significantly greater memory storage, such as the Flash memory used on USB sticks, and require much less energy and space.

The team’s new ReRAM technology was discovered by accident whilst engineers at UCL were working on using the silicon oxide material to produce silicon-based LEDs. During the course of the project, researchers noticed that their devices appeared to be unstable. UCL Department of Electronic and Electrical Engineering PhD student Adnan Mehonic was asked to look for a solution by observing material’s electrical properties, where he discovered that the material wasn’t unstable at all, but flipped between various conducting and non-conducting states in a predictable fashion.

ReRAM memory chips whose electrical resistance changes when voltage is applied, and this change in state is kept even when the power is turned off. Unlike other silicon oxide chips currently in development, the UCL chip does not require a vacuum to work, and is therefore potentially less costly and more durable.

The UCL team managed to develop ReRAM memory which performs the switch in resistance much more efficiently than has been previously achieved. In their material, the arrangement of the silicon atoms changes to form filaments of silicon within the solid silicon oxide, which are less resistive. The presence or absence of these filaments represents a ‘switch’ from one state to another.

“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”, said Dr Tony Kenyon, UCL Electronic and Electrical Engineering. “We are also working on making a quartz device with a view to developing transparent electronics.”

For added flexibility, the UCL devices can also be designed to have a continuously variable resistance that depends on the last voltage that was applied. This is an important property that allows the device to mimic how neurons in the brain function. Devices that operate in this way are sometimes known as ‘memristors’.

“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”, said Mehonic.

The technology has promising applications beyond memory storage. The team is also exploring using the resistance properties of their material not just for use in memory but also as a computer processor. The design also raises the possibility of transparent memory chips for use in touch screens and mobile devices.

This technology is currently of enormous interest, with the first practical memristor, based on titanium dioxide, demonstrated in just 2008. The development of a silicon oxide memristor is a huge step forward because of the potential for its incorporation into silicon chips.

The team has been backed by UCLB, UCL’s technology transfer company, and they recently filed a patent on the device. Discussions are ongoing with a number of leading semiconductor companies.

For more information, read the paper in the Journal of Applied Physics: “Resistive switching in silicon suboxide films”.