Graphene may enable dense, energy-efficient memory chips

Researchers at Stanford University have recently performed three separate experiments that suggest graphene in computing and telecommunications could radically cut energy consumption. This work was done in search of post-silicon materials and technologies that enable storing more data per square inch and use a fraction of the energy of currently used memory chips.

All three experiments involve graphene, and test different ways to use it in new storage technologies. The scientists claim that graphene can have interesting mobile applications of these new technologies, but post-silicon memory chips may transform server farms that store and deliver quick access to enormous quantities of data stored in the cloud.

Most of the currently known memory chips are based on silicon, and come in two basic types volatile and non-volatile. Volatile memory, such as random access memory (RAM), offers fast but temporary storage. When the power shuts off, the zeros and ones disappear. Non-volatile memory, such as the flash memory in cell phones, is slower but stable - even if the battery expires the data remains. The Stanford-led engineers managed to create memory with the speed of RAM and the persistence of flash by using new materials and technologies that require less energy than silicon to store the zeroes and ones.

One of the experiments involved a technique known as resistive random-access memory, or RRAM for short. In RRAM chips, tiny jolts of electricity switch certain metal oxides between resistive and conductive states. When the metal oxides resist the flow of electrons, a zero is created. When the materials conduct electrons, that is a one. RRAM is fast, like volatile silicon memory, but like flash memory it retains stored data when the power is turned off.

The other two experiments used graphene to make advances with a different but conceptually similar storage approach called phase-change memory. In phase-change memory, a tiny jolt of electricity causes an alloy of germanium, antimony and tellurium to change its atomic structure. One jolt tweaks the atoms into a regular, crystalline structure that allows electrons to flow, notated as a digital one. A second jolt makes the structure irregular, or amorphous, creating a zero. Each jolt quickly pushes the phase-change material from one to zero. Like RRAM, it retains its stored data when the power is turned off. 

One of these experiments had the scientists use ribbons of graphene as ultra-thin electrodes to intersect phase-change memory cells. This setup also exploited the atomically thin edge of graphene to push current into the material, and change its phase, again in an extremely energy-efficient manner. In the other experiment, the scientists used both the electrical and thermal properties of graphene in a phase-change memory chip. However, here they used the surface of the graphene sheet to contact the phase-change memory alloy. In essence, the graphene prevented the heat from leaking out of the phase-change material, creating a more energy-efficient memory cell.

The researchers maintain that these experiments show that graphene is far from a laboratory curiosity and that the material's unique properties can be utilized to create more energy-efficient data storage and possibly someday present a viable alternative to silicon.