A team of Russian and French researchers bonded a piezoelectric material to magneto-elastic magnetoelastic layers of a terbium-cobalt alloy (TbCo2) and an alloy of iron and cobalt (FeCo) to create a nonvolatile memory architecture that could decrease the required read/write energy of traditional memories by a factor of 10,000 or more.
The key to achieving the ultralow-power magnetoelectric RAM (MELRAM), according to the researchers, was to abandon giant magnetoresistive stacks and magnetic tunnel junctions. The demonstration architecture instead relies on magnetoelectric interactions for readout of the information coded in the magnetic subsystem when an electric field is applied, accomplished via a composite multiferroic heterostructure using piezoelectrically stress-mediated magnetoelectronics.
The downside is that reading destroys the memory state, which must be rewritten after each read, the researchers report in “Magnetoelectric write and read operations in a stress-mediated multiferroic memory cell.” Despite that drawback , the American Institute of Physics published the researchers’ results in the peer-reviewed Applied Physics Letters because achievement of a 10,000x reduction in energy would outweigh the necessity of rewriting after each read. In fact, the authors claim that 99 percent of the consumed power of today’s memory systems is wasted in the form of heat.
In more detail, because the material is anisotropic, when the read/write voltage is applied to the memory cell the piezoelectric layer deforms, setting either a 1 or 0 depending on polarity (see illustration). When a read current is applied, the resulting voltage reveals whether the state is a 1 or a 0, but the bit state is destroyed during reading.
All operations in the demonstration chip were performed at room temperature. The millimeter-sized demonstration cell can be scaled down to the size of traditional RAM cells, according to the researchers.
The collaborators hailed from the University of Valenciennes (France); the Moscow Institute of Physics and Technology (MIPT); the Moscow Technological University (MIREA); the Kotelnikov Institute of Radio Engineering and Electronics (IRE) of the Russian Academy of Sciences (RAS); and the International Associated Laboratory of the Critical and Supercritical Phenomena in Functional Electronics, Acoustics, and Fluidics (Moscow). The principal investigator was Sergei Nikitov, who is deputy head of MIPT’ s Section of Solid State Physics, Radiophysics, and Applied Information Technologies; a corresponding member of RAS; and the director of IRE RAS.