What is a Resistive RAM?

A RRAM is a device that can switch between one or more resistances under the application of appropriate voltages. Devices can have two or more discrete resistance states, or may have a continuously variable resistance. Whatever the case, it is important that the change in resistance is governed by the past history of the device - that is, by the previous voltage applied, or the previous current that has flowed through the device.

What is the difference between a RRAM and a memristor?

There is currently some controversy over this. A memristor is a device whose resistance depends on its past history - more precisely, it depends on the flux of electric charge through the device. In this sense, a RRAM is a device that shows memristive behaviour, and can be thought of as a specific type of memristor.

Why are RRAMs and memristors of interest?

RRAM devices may help overcome some of the bottlenecks that we are currently facing in microelectronics. As we shrink the size of the transistors that make up semiconductor memories further and further we run into problems of fabrication difficulty, power dissipation and switching speed. RRAM devices can be packed much more densely. fabricated in 3D arrays, and have very low switching energies and fast switching speeds.

In addition, devices whose state depends on their past history behave in some ways similarly to neurons - RRAMs and memristors can thus be used to fabricate very high density neural networks.

What is the UCL Resistive RAM?

We have developed, and filed a patent on, a RRAM device based wholly on the Si/SiO2 system. Unlike competing technologies, it does not rely on the diffusion of metal ions, can be fabricated only from n- and p- type silicon and silicon oxide, and operates in ambient conditions. Resistance contrast is up to 5 orders of magnitude, switching time 90ns or shorter, and switching energy is 1pJ/bit or lower. Scanning Tunneling Microscopy suggests that the individual switching elements may be as small as 10nm.

How does the UCL RRAM compare to existing technologies?

As an indication of the capabilities of this device, the table below shows the specifications achieved to date, alongside those of conventional Flash memory, and target specifications for our next generation of devices.

Further information

Contact us

A. Mehonic, S. Cueff, M. Wojdak, S. Hudziak, O. Jambois, C. Labbe, B. Garrido, R. Rizk & A.J. Kenyon, “Resistive switching in silicon sub-oxide films”, J. Appl. Phys. 111, 074507 (2012)

BBC article on our RRAM device

IEEE Spectrum article on our RRAM device

Coverage of our device by the IET

More about RRAM and memristors

ITRS report on emerging memory devices

More on memristors

HP TiOx memristor

Resistive RAM