“Researchers from Tel Aviv University have engineered what has been described as the “world’s tiniest technology”, opening up the possibility of storing information in the thinnest devices ever seen using “slidetronics”.
The unit is just two atoms thick; it is made up of ‘sliding’ 2D layers of boron and nitrogen, through which electrons may tunnel, boosting the information reading process beyond current technologies.
Current state-of-the-art nano storage devices are at least 100 atoms thick, containing around a million atoms in a crystalline structure. Approximately a million of these devices could fit into the area of a coin, each switching at a speed of a million times per second.
“Our research stems from curiosity about the behaviour of atoms and electrics in solid materials, which has generated many of the technologies supporting our modern way of life,” said Professor Moshe Ben Shalom. “We, and many other scientists, try to understand, predict, and even control the fascinating properties of these particles as they condense into an ordered structure that we call a crystal. At the heart of the computer, for example, lies a tiny crystalline device designed to switch between the two states indicating different responses: yes or no, up or down. Without this dichotomy, it is not possible to encode and process information.
“The practical challenge is to find a mechanism that would enable switching in a small, fast, and inexpensive device.”
The researchers were able to reduce the thickness of data storage devices to just two atoms, for which information is based on the ability of electrons to tunnel through the thin structure. This could significantly boost the speed, density, and energy consumption of electronic devices.
The 2D layers used to create the device contain boron and nitrogen arranged in a repetitive hexagonal crystalline structure. The researchers were able to break the symmetry of this crystal by artificially assembling two such layers; in its natural (3D) state, the material contains many antiparallel layers (each rotated 180 degrees relative to its neighbours). In the lab they stacked just two layers in a parallel configuration, theoretically placing atoms of the same kind in immaculate overlap in spite of the repulsive electrostatic forces between them.
In practice, the flakes of crystal “prefer” to slide one layer slightly in relation to the other, such that half of each layer’s atoms are in perfect overlap, with opposite charges overlapping, while the rest are located above or below a gap in the centre of a hexagon. “If in the top layer only the boron atoms overlap, in the bottom layer it’s the other way around,” explained Ben Shalom.
The fundamental reasoning for this arrangement was elucidated by theorists using computer simulations.
Maayan Wizner Stern, a PhD candidate who led the study, explained how the device works: “The symmetry breaking we created in the laboratory – which does not exist in the natural crystal – forces the electric charge to reorganise itself between the layers and generate a tiny internal electrical polarisation perpendicular to the layer plane.
“When we apply an external electric field in the opposite direction, the system slides laterally to switch polarisation orientation. The switched polarisation remains stable even when the external field is shut down. In this, the system is similar to 3D ferroelectric systems, which are widely used in technology today.”
According to the scientists, the ability to force this arrangement in such a thin system is not limited to the boron and nitrogen crystal: “We expect the same behaviours in many layered crystals with the right symmetry properties. The concept of interlayer sliding as an original and efficient way to control advanced electronic devices is very promising, and we have named it slidetronics.”
Vizner Stern concluded: “We are excited about discovering what can happen in other states we force upon nature and predict that other structures that couple additional degrees of freedom are possible. We hope that miniaturisation and flipping through sliding will improve today’s electronic devices, and moreover, allow other original ways of controlling information in future devices.
“In addition to computer devices, we expect that this technology will contribute to detectors, energy storage and conversion, interaction with light, etc. Our challenge, as we see it, is to discover more crystals with new and slippery degrees of freedom.””