A new memory cell based on superconductors, which can work hundreds of times faster than currently available devices, has been developed by Russian engineers.
The memory cell, relying on quantum effects in sandwiches of superconducting and dielectric materials, stores information in the form of the superconducting current. This presents a potential advantage over conventional memory cells storing information as the direction of the magnetic field vector in a ferromagnet.
“With the operational function that we have proposed in these memory cells, there will be no need for time-consuming magnetisation and demagnetisation processes,” explained Alexander Golubov, head of the Laboratory of Quantum Topological Phenomena in Superconducting Systems at the Moscow Institute of Physics and Technology, one of the authors of the study published in the latest issue of the journal Applied Physics Letters.
“This means that read and write operations will take only a few hundred picoseconds, depending on the materials and the geometry of the particular system, while conventional methods take hundreds or thousands of times longer than this.”
The system encodes bits of information as zeroes and ones in two energy minima, which the team found in the sandwiches. In order to switch the system from zero to one and back again, the scientists have suggested using injection currents flowing through one of the layers of the superconductor. They propose to read the status using the current that flows through the whole structure. These operations can be performed hundreds of times faster than measuring the magnetisation or magnetisation reversal of a ferromagnet.
“In addition, our method requires only one ferromagnetic layer, which means that it can be adapted to so-called single flux quantum logic circuits, and this means that there will be no need to create an entirely new architecture for a processor,” Golubov said. “A computer based on single flux quantum logic can have a clock speed of hundreds of gigahertz, and its power consumption will be dozens of times lower."
Quantum effects in sandwiches of superconducting materials with a dielectric layer in the middle were predicted in the 1960s by British physicist Brian Josephson, after whom those sandwiches have been named Josephson junctions. The electrons in these junctions are able to tunnel from one layer of a superconductor to another, passing through the dielectric-like balls passing through a perforated wall.
Today, Josephson junctions are used both in quantum devices and conventional devices. Josephson junctions with ferromagnets as the middle layer of the sandwich are being used in ferromagnetic memory devices. However, these systems are rather slow when reading and writing data.