Manufacturing Bits: July 10
Researchers study behavior of ferroelectrics
Today’s memories based on ferroelectric materials are difficult to scale and are mainly used for niche applications like SRAM replacements in battery-backed systems.
The U.S. Department of Energy’s Brookhaven National Laboratory, Lawrence Berkeley National Laboratory and others have revealed details about the atomic structure and behavior of ferroelectric materials. This could lead the way to next-generation or universal memories based on ferroelectric materials.
Brookhaven has devised a technique called electron holography to capture images of the electric fields created by the ferroelectric materials’ atomic displacement. The laboratory also demonstrated a method for identifying the behavior and stability of ferroelectrics.
Direct polarization images of individual ferroelectric nano cubes captured with electron holography. The fringing field, or “footprint” of electric polarization, can be seen clearly in (a), but it vanishes when the material is subjected to high temperatures (b). The lower images show that no fringing field can be observed before application of electricity (c), but a clear field emanates after current is applied (d).
Understanding the atomic-scale properties will help guide implementation of these particles. “Electron holography is an interferometry technique using coherent electron waves,” said Brookhaven physicist Myung-Geun Han. “When electron waves pass through a ferroelectric sample, they are influenced by local electric fields, yielding a so-called phase-shift. The interference pattern between the electrons that pass through electric fields and those that don’t creates what’s called an electron hologram, which allows us to directly ‘see’ those local electric fields around individual ferroelectric nano particles.”
With this technique, researchers revealed that the electric polarity could remain stable for individual ferroelectric materials. This means that each nanoparticle can be used as a data bit.
“Properly used, ferroelectrics could ramp up memory density and store an unparalleled multiple terabytes of information on just one square inch of electronics,” Han said. “This brings us closer to engineering such devices.”
The ferroelectric nanoparticles tested, semiconducting germanium telluride and insulating barium titanate, were engineered at Lawrence Berkeley National Laboratory. They were brought to Brookhaven Lab for the electron holography experiments. Additional experiments using x-ray diffraction were conducted at Argonne National Laboratory’s Advanced Photon Source.
The University of California at Berkeley, the University of New Orleans and Central Michigan University also collaborated with the work. The research was funded by Department of Energy’s Office of Science. The research will be published in Nature Materials.
Researchers devise molecular spintronic devices
A molecular switch can be used to store information in a single molecule. Adding spin functionality to molecular switches is a key technology to enable a next-generation memory device.
The research was conducted by Karlsruhe Institute of Technology, Institut de Physique et Chimie des Matériaux de Strasbourg, Chiba University and Synchrotron SOLEIL.
To enable these devices, researchers devised spin-crossover complexes. This consists of a transition metal ion that can be switched between a low-spin (LS) and a high-spin (HS) state by external stimuli. The two configurations may lead to different conductances.
As part of the process, researchers made use of individual Fe-phen molecules at low temperature with high lateral and energy resolution. The Fe-phen molecules, which were adsorbed onto a copper surface, exhibited the coexistence of HS and LS states.
But the strong coupling of the materials to the substrate prevents a spin state from being written electrically. Introducing an interfacial copper nitride layer allows switching between the HS and the LS state. The combined changes in conductance and spin state demonstrate how to confer memristive to spintronic properties, realizing multifunctional spintronic capacity in single molecules.
The paper has been published in Nature Communications.
—Mark LaPedus
Tags: Brookhaven Natinoal Laboratory, Central Michigan University, Chiba University, Department of Energy, electron holography, ferroelectrics, Institut de Physique et Chimie des Materiaux de Strasbourg, Karlsruhe Institute Of Technology, Lawrence Berkeley National Laboratory, spintronics, Synchroton Soleil, UC Berkeley, University of New Orleans