Fast-moving spinning magnetized nanoparticles could lead to ultra-high-speed, high-density data storage

Artist’s impression of skyrmion data storage (credit: Moritz Eisebitt)

An international team led by MIT associate professor of materials science and engineering Geoffrey Beach has demonstrated a practical way to use “skyrmions” to create a radical new high-speed, high-density data-storage method that could one day replace disk drives — and even replace high-speed RAM memory.

Rather than reading and writing data one bit at a time by changing the orientation of magnetized nanoparticles on a surface, Skyrmions could store data using only a tiny area of a magnetic surface — perhaps just a few atoms across — and for long periods of time, without the need for further energy input (unlike disk drives and RAM).

Beach and associates conceive skyrmions as little sub-nanosecond spin-generating eddies of magnetism controlled by electric fields — replacing the magnetic-disk system of reading and writing data one bit at a time. In experiments, skyrmions have been generated on a thin metallic film sandwiched with non-magnetic heavy metals and transition-metal ferromagnetic layers — exploiting a defect, such as a constriction in the magnetic track.*

Skyrmions are also highly stable to external magnetic and mechanical perturbations, unlike the individual magnetic poles in a conventional magnetic storage device — allowing for vastly more data to be written onto a surface of a given size.

A practical data-storage system

Google data center (credit: Google Inc.)

Beach has recently collaborated with researchers at MIT and others in Germany** to demonstrate experimentally for the first time that it’s possible to create skyrmions in specific locations, which is needed for a data-storage system. The new findings were reported October 2, 2017 in the journal Nature Nanotechnology.

Conventional magnetic systems are now reaching speed and density limits set by the basic physics of their existing materials. The new system, once perfected, could provide a way to continue that progress toward ever-denser data storage, Beach says.

However, the researchers note that to create a commercialized system will require an efficient, reliable way to create skyrmions when and where they were needed, along with a way to read out the data (which now requires sophisticated, expensive X-ray magnetic spectroscopy). The team is now pursuing possible strategies to accomplish that.***

* The system focuses on the boundary region between atoms whose magnetic poles are pointing in one direction and those with poles pointing the other way. This boundary region can move back and forth within the magnetic material, Beach says. What he and his team found four years ago was that these boundary regions could be controlled by placing a second sheet of nonmagnetic heavy metal very close to the magnetic layer. The nonmagnetic layer can then influence the magnetic one, with electric fields in the nonmagnetic layer pushing around the magnetic domains in the magnetic layer. Skyrmions are little swirls of magnetic orientation within these layers. The key to being able to create skyrmions at will in particular locations lays in material defects. By introducing a particular kind of defect in the magnetic layer, the skyrmions become pinned to specific locations on the surface, the team found. Those surfaces with intentional defects can then be used as a controllable writing surface for data encoded in the skyrmions.

** The team also includes researchers at the Max Born Institute and the Institute of Optics and Atomic Physics, both in Berlin; the Institute for Laser Technologies in Medicine and Metrology at the University of Ulm, in Germany; and the Deutches Elektroniken-Syncrotron (DESY), in Hamburg. The work was supported by the U.S. Department of Energy and the German Science Foundation.

*** The researchers believe an alternative way of reading the data is possible, using an additional metal layer added to the other layers. By creating a particular texture on this added layer, it may be possible to detect differences in the layer’s electrical resistance depending on whether a skyrmion is present or not in the adjacent layer.


Abstract of Field-free deterministic ultrafast creation of magnetic skyrmions by spin–orbit torques

Magnetic skyrmions are stabilized by a combination of external magnetic fields, stray field energies, higher-order exchange interactions and the Dzyaloshinskii–Moriya interaction (DMI). The last favours homochiral skyrmions, whose motion is driven by spin–orbit torques and is deterministic, which makes systems with a large DMI relevant for applications. Asymmetric multilayers of non-magnetic heavy metals with strong spin–orbit interactions and transition-metal ferromagnetic layers provide a large and tunable DMI. Also, the non-magnetic heavy metal layer can inject a vertical spin current with transverse spin polarization into the ferromagnetic layer via the spin Hall effect. This leads to torques that can be used to switch the magnetization completely in out-of-plane magnetized ferromagnetic elements, but the switching is deterministic only in the presence of a symmetry-breaking in-plane field. Although spin–orbit torques led to domain nucleation in continuous films and to stochastic nucleation of skyrmions in magnetic tracks, no practical means to create individual skyrmions controllably in an integrated device design at a selected position has been reported yet. Here we demonstrate that sub-nanosecond spin–orbit torque pulses can generate single skyrmions at custom-defined positions in a magnetic racetrack deterministically using the same current path as used for the shifting operation. The effect of the DMI implies that no external in-plane magnetic fields are needed for this aim. This implementation exploits a defect, such as a constriction in the magnetic track, that can serve as a skyrmion generator. The concept is applicable to any track geometry, including three-dimensional designs.

New transistor design enables flexible, high-performance wearable/mobile electronics

Advanced flexible transistor developed at UW-Madison (photo credit: Jung-Hun Seo/University at Buffalo, State University of New York)

A team of University of Wisconsin–Madison (UW–Madison) engineers has created “the most functional flexible transistor in the world,” along with a fast, simple, inexpensive fabrication process that’s easily scalable to the commercial level.

The development promises to allow manufacturers to add advanced, smart-wireless capabilities to wearable and mobile devices that curve, bend, stretch and move.*

The UW–Madison group’s advance is based on a BiCMOS (bipolar complementary metal oxide semiconductor) thin-film transistor, combining speed, high current, and low power dissipation (heat and wasted energy) on just one surface (a silicon nanomembrane, or “Si NM”).**

BiCMOS transistors are the chip of choice for “mixed-signal” devices (combining analog and digital capabilities), which include many of today’s portable electronic devices such as cellphones. “The [BiCMOS] industry standard is very good,” says Zhenqiang (Jack) Ma, the Lynn H. Matthias Professor and Vilas Distinguished Achievement Professor in electrical and computer engineering at UW–Madison. “Now we can do the same things with our transistor — but it can bend.”

The research was described in the inaugural issue of Nature Publishing Group’s open-access journal Flexible Electronics, published Sept. 27, 2017.***

Making traditional BiCMOS flexible electronics is difficult, in part because the process takes several months and requires a multitude of delicate, high-temperature steps. Even a minor variation in temperature at any point could ruin all of the previous steps.

Ma and his collaborators fabricated their flexible electronics on a single-crystal silicon nanomembrane on a single bendable piece of plastic. The secret to their success is their unique process, which eliminates many steps and slashes both the time and cost of fabricating the transistors.

“In industry, they need to finish these in three months,” he says. “We finished it in a week.”

He says his group’s much simpler, high-temperature process can scale to industry-level production right away.

“The key is that parameters are important,” he says. “One high-temperature step fixes everything — like glue. Now, we have more powerful mixed-signal tools. Basically, the idea is for [the flexible electronics platform] to expand with this.”

* Some companies (such as Samsung) have developed flexible displays, but not other flexible electronic components in their devices, Ma explained to KurzweilAI.

** “Flexible electronics have mainly focused on their form factors such as bendability, lightweight, and large area with low-cost processability…. To date, all the [silicon, or Si]-based thin-film transistors (TFTs) have been realized with CMOS technology because of their simple structure and process. However, as more functions are required in future flexible electronic applications (i.e., advanced bioelectronic systems or flexible wireless power applications), an integration of functional devices in one flexible substrate is needed to handle complex signals and/or various power levels.” — Jung Hun Seo et al./Flexible Electronics. The n-channel, p-channel metal-oxide semiconductor field-effect transistors (N-MOSFETs & P-MOSFETs), and NPN bipolar junction transistors (BJTs) were realized together on a 340-nm thick Si NM layer. 

*** Co-authors included researchers at the University at Buffalo, State University of New York, and the University of Texas at Arlington. This work was supported by the Air Force Office Of Scientific Research.


Abstract of High-performance flexible BiCMOS electronics based on single-crystal Si nanomembrane

In this work, we have demonstrated for the first time integrated flexible bipolar-complementary metal-oxide-semiconductor (BiCMOS) thin-film transistors (TFTs) based on a transferable single crystalline Si nanomembrane (Si NM) on a single piece of bendable plastic substrate. The n-channel, p-channel metal-oxide semiconductor field-effect transistors (N-MOSFETs & P-MOSFETs), and NPN bipolar junction transistors (BJTs) were realized together on a 340-nm thick Si NM layer with minimized processing complexity at low cost for advanced flexible electronic applications. The fabrication process was simplified by thoughtfully arranging the sequence of necessary ion implantation steps with carefully selected energies, doses and anneal conditions, and by wisely combining some costly processing steps that are otherwise separately needed for all three types of transistors. All types of TFTs demonstrated excellent DC and radio-frequency (RF) characteristics and exhibited stable transconductance and current gain under bending conditions. Overall, Si NM-based flexible BiCMOS TFTs offer great promises for high-performance and multi-functional future flexible electronics applications and is expected to provide a much larger and more versatile platform to address a broader range of applications. Moreover, the flexible BiCMOS process proposed and demonstrated here is compatible with commercial microfabrication technology, making its adaptation to future commercial use straightforward.

Ray Kurzweil on The Age of Spiritual Machines: A 1999 TV interview

Dear readers,

For your interest, this 1999 interview with me, which I recently re-watched, describes some interesting predictions that are still coming true today. It’s intriguing to look back at the last 18 years to see what actually unfolded. This video is a compelling glimpse into the future, as we’re living it today.

Enjoy!

— Ray


Dear readers,

This interview by Harold Hudson Channer was recorded on Jan. 14, 1999 and aired February 1, 1999 on a Manhattan Neighborhood Network cable-access show, Conversations with Harold Hudson Channer.

In the discussion, Ray explains many of the ahead-of-their-time ideas presented in The Age of Spiritual Machines*, such as the “law of accelerating returns” (how technological change is exponential, contrary to the common-sense “intuitive linear” view); the forthcoming revolutionary impacts of AI; nanotech brain and body implants for increased intelligence, improved health, and life extension; and technological impacts on economic growth.

I was personally inspired by the book in 1999 and by Ray’s prophetic, uplifting vision of the future. I hope you also enjoy this blast from the past.

— Amara D. Angelica, Editor

* First published in hardcover January 1, 1999 by Viking. The series also includes The Age of Intelligent Machines (The MIT Press, 1992) and The Singularity Is Near (Penquin Books, 2006).

Walking DNA nanorobot could deliver a drug to a precise location in your body

DNA nanorobot cargo carrier (artist’s impression) (credit: Ella Maru Studio)

Caltech scientists have developed a “cargo sorting” DNA nanorobot programmed to autonomously “walk” around a surface, pick up certain molecules, and drop them off in designated locations.

The research is described in a paper in the Friday, September 15, 2017 issue of Science.

The major advance in this study is “their methodology for designing simple DNA devices that work in parallel to solve nontrivial tasks,” notes Duke University computer scientist John H. Reif in an article in the same issue of Science.

Such tasks could include synthesizing a drug in a molecular factory or delivering a drug only when a specific signal is present in bloodstreams, say the researchers. “So far, the development of DNA robots has been limited to simple functions,” the researchers note.

Walking nanobots that work in parallel

Conceptual illustration of two DNA nanorobots collectively performing a cargo-sorting task on a DNA origami surface: transporting fluorescent molecules with different colors from initially random locations to ordered destinations. (credit: Demin Liu)

The DNA nanorobot, intended as a proof of concept, has a “leg” with two “feet” for walking, and an “arm” and “hand” for picking up cargo. It also has a segment that can recognize a specific drop-off point and signal to the hand to release its cargo. Each of these building blocks are made of just a few nucleotides (molecules that form DNA) within a single strand of DNA.*

As the robot encounters cargo molecules tethered to pegs, it grabs them with its “hand” components and carries them around (with a 6-nm step size) until it detects the signal of the drop-off point.

Multiple DNA nanorobots independently execute three operations in parallel: [1] cargo pickup, [2] random movement to adjacent stepping stones, and [3] cargo drop-off at ordered locations. (credit: C. Bickel/Science)

In experiments, the nanorobots successfully sorted six randomly scattered molecules into their correct places in 24 hours. The process is slow, but adding more robots to the surface shortened the time it took to complete the task. The very simple robot design utilizes very little chemical energy, according to the researchers.**

“The same system design can be generalized to work with dozens of types of cargos at any arbitrary initial location on the surface,” says lead author Anupama Thubagere. “One could also have multiple robots performing diverse sorting tasks in parallel,” [programmed] like macroscopic robots.”

Future applications

“We don’t develop DNA robots for any specific applications. Our lab focuses on discovering the engineering principles that enable the development of general-purpose DNA robots,” explains Lulu Qian, assistant professor of bioengineering.

“However, it is my hope that other researchers could use these principles for exciting applications, such as synthesizing a therapeutic chemical from its constituent parts in an artificial molecular factory, or sorting molecular components in trash for recycling. Just like electromechanical robots are sent off to faraway places, like Mars, we would like to send molecular robots to minuscule places where humans can’t go, such as the bloodstream.”

Funding was provided by Caltech Summer Undergraduate Research Fellowships, the National Science Foundation, and the Burroughs Wellcome Fund.

* The key to designing DNA machines is the fact that DNA has unique chemical and physical properties that are known and programmable. A single strand of DNA is made up of four different molecules called nucleotides—abbreviated A, G, C, and T—and arranged in a string called a sequence. These nucleotides bond in specific pairs: A with T, and G with C. When a single strand encounters a “reverse complementary strand” — for example, CGATT meets AATCG —the two strands zip together in the classic double-helix shape.

** Using these chemical and physical principles, researchers can also design “playgrounds,” such as molecular pegboards, to test them on, according to the researchers. In the current work, the DNA robot moves around on a 58-nanometer-by-58-nanometer pegboard on which the pegs are made of single strands of DNA complementary to the robot’s leg and foot. The robot binds to a peg with its leg and one of its feet — the other foot floats freely. When random molecular fluctuations cause this free foot to encounter a nearby peg, it pulls the robot to the new peg and its other foot is freed. This process continues with the robot moving in a random direction at each step.


Abstract of A cargo-sorting DNA robot

Two critical challenges in the design and synthesis of molecular robots are modularity and
algorithm simplicity.We demonstrate three modular building blocks for a DNA robot that
performs cargo sorting at themolecular level. A simple algorithm encoding recognition between
cargos and their destinations allows for a simple robot design: a single-stranded DNA with
one leg and two foot domains for walking, and one arm and one hand domain for picking up and
dropping off cargos.The robot explores a two-dimensional testing ground on the surface of
DNA origami, picks up multiple cargos of two types that are initially at unordered locations, and
delivers them to specified destinations until all molecules are sorted into two distinct piles.
The robot is designed to perform a random walk without any energy supply. Exploiting this
feature, a single robot can repeatedly sort multiple cargos. Localization on DNA origami allows
for distinct cargo-sorting tasks to take place simultaneously in one test tube or for multiple
robots to collectively perform the same task.

Radical new vertically integrated 3D chip design combines computing and data storage

Four vertical layers in new 3D nanosystem chip. Top (fourth layer): sensors and more than one million carbon-nanotube field-effect transistor (CNFET) logic inverters; third layer, on-chip non-volatile RRAM (1 Mbit memory); second layer, CNFET logic with classification accelerator (to identify sensor inputs); first (bottom) layer, silicon FET logic. (credit: Max M. Shulaker et al./Nature)

A radical new 3D chip that combines computation and data storage in vertically stacked layers — allowing for processing and storing massive amounts of data at high speed in future transformative nanosystems — has been designed by researchers at Stanford University and MIT.

The new 3D-chip design* replaces silicon with carbon nanotubes (sheets of 2-D graphene formed into nanocylinders) and integrates resistive random-access memory (RRAM) cells.

Carbon-nanotube field-effect transistors (CNFETs) are an emerging transistor technology that can scale beyond the limits of silicon MOSFETs (conventional chips), and promise an order-of-magnitude improvement in energy-efficient computation. However, experimental demonstrations of CNFETs so far have been small-scale and limited to integrating only tens or hundreds of devices (see earlier 2015 Stanford research, “Skyscraper-style carbon-nanotube chip design…”).

The researchers integrated more than 1 million RRAM cells and 2 million carbon-nanotube field-effect transistors in the chip, making it the most complex nanoelectronic system ever made with emerging nanotechnologies, according to the researchers. RRAM is an emerging memory technology that promises high-capacity, non-volatile data storage, with improved speed, energy efficiency, and density, compared to dynamic random-access memory (DRAM).

Instead of requiring separate components, the RRAM cells and carbon nanotubes are built vertically over one another, creating a dense new 3D computer architecture** with interleaving layers of logic and memory. By using ultradense through-chip vias (electrical interconnecting wires passing between layers), the high delay with conventional wiring between computer components is eliminated.

The new 3D nanosystem can capture massive amounts of data every second, store it directly on-chip, perform in situ processing of the captured data, and produce “highly processed” information. “Such complex nanoelectronic systems will be essential for future high-performance, highly energy-efficient electronic systems,” the researchers say.

How to combine computation and storage

Illustration of separate CPU (bottom) and RAM memory (top) in current computer architecture (images credit: iStock)

The new chip design aims to replace current chip designs, which separate computing and data storage, resulting in limited-speed connections.

Separate 2D chips have been required because “building conventional silicon transistors involves extremely high temperatures of over 1,000 degrees Celsius,” explains lead author Max Shulaker, an assistant professor of electrical engineering and computer science at MIT and lead author of a paper published July 5, 2017 in the journal Nature. “If you then build a second layer of silicon circuits on top, that high temperature will damage the bottom layer of circuits.”

Instead, carbon nanotube circuits and RRAM memory can be fabricated at much lower temperatures: below 200 C. “This means they can be built up in layers without harming the circuits beneath,” says Shulaker.

Overcoming communication and computing bottlenecks

As applications analyze increasingly massive volumes of data, the limited rate at which data can be moved between different chips is creating a critical communication “bottleneck.” And with limited real estate on increasingly miniaturized chips, there is not enough room to place chips side-by-side.

At the same time, embedded intelligence in areas ranging from autonomous driving to personalized medicine is now generating huge amounts of data, but silicon transistors are no longer improving at the historic rate that they have for decades.

Instead, three-dimensional integration is the most promising approach to continue the technology-scaling path set forth by Moore’s law, allowing an increasing number of devices to be integrated per unit volume, according to Jan Rabaey, a professor of electrical engineering and computer science at the University of California at Berkeley, who was not involved in the research.

Three-dimensional integration “leads to a fundamentally different perspective on computing architectures, enabling an intimate interweaving of memory and logic,” he says. “These structures may be particularly suited for alternative learning-based computational paradigms such as brain-inspired systems and deep neural nets, and the approach presented by the authors is definitely a great first step in that direction.”

The new 3D design provides several benefits for future computing systems, including:

  • Logic circuits made from carbon nanotubes can be an order of magnitude more energy-efficient compared to today’s logic made from silicon.
  • RRAM memory is denser, faster, and more energy-efficient compared to conventional DRAM (dynamic random-access memory) devices.
  • The dense through-chip vias (wires) can enable vertical connectivity that is 1,000 times more dense than conventional packaging and chip-stacking solutions allow, which greatly improves the data communication bandwidth between vertically stacked functional layers. For example, each sensor in the top layer can connect directly to its respective underlying memory cell with an inter-layer via. This enables the sensors to write their data in parallel directly into memory and at high speed.
  • The design is compatible in both fabrication and design with today’s CMOS silicon infrastructure.

Shulaker next plans to work with Massachusetts-based semiconductor company Analog Devices to develop new versions of the system.

This work was funded by the Defense Advanced Research Projects Agency, the National Science Foundation, Semiconductor Research Corporation, STARnet SONIC, and member companies of the Stanford SystemX Alliance.

* As a working-prototype demonstration of the potential of the technology, the researchers took advantage of the ability of carbon nanotubes to also act as sensors. On the top layer of the chip, they placed more than 1 million carbon nanotube-based sensors, which they used to detect and classify ambient gases for detecting signs of disease by sensing particular compounds in a patient’s breath, says Shulaker. By layering sensing, data storage, and computing, the chip was able to measure each of the sensors in parallel, and then write directly into its memory, generating huge bandwidth in just one device, according to Shulaker. The top layer could be replaced with additional computation or data storage subsystems, or with other forms of input/output, he explains.

** Previous R&D in 3D chip technologies and their limitations are covered here, noting that “in general, 3D integration is a broad term that includes such technologies as 3D wafer-level packaging (3DWLP); 2.5D and 3D interposer-based integration; 3D stacked ICs (3D-SICs), monolithic 3D ICs; 3D heterogeneous integration; and 3D systems integration.” The new Stanford-MIT nanosystem design significantly expands this definition.


Abstract of Three-dimensional integration of nanotechnologies for computing and data storage on a single chip

The computing demands of future data-intensive applications will greatly exceed the capabilities of current electronics, and are unlikely to be met by isolated improvements in transistors, data storage technologies or integrated circuit architectures alone. Instead, transformative nanosystems, which use new nanotechnologies to simultaneously realize improved devices and new integrated circuit architectures, are required. Here we present a prototype of such a transformative nanosystem. It consists of more than one million resistive random-access memory cells and more than two million carbon-nanotube field-effect transistors—promising new nanotechnologies for use in energy-efficient digital logic circuits and for dense data storage—fabricated on vertically stacked layers in a single chip. Unlike conventional integrated circuit architectures, the layered fabrication realizes a three-dimensional integrated circuit architecture with fine-grained and dense vertical connectivity between layers of computing, data storage, and input and output (in this instance, sensing). As a result, our nanosystem can capture massive amounts of data every second, store it directly on-chip, perform in situ processing of the captured data, and produce ‘highly processed’ information. As a working prototype, our nanosystem senses and classifies ambient gases. Furthermore, because the layers are fabricated on top of silicon logic circuitry, our nanosystem is compatible with existing infrastructure for silicon-based technologies. Such complex nano-electronic systems will be essential for future high-performance and highly energy-efficient electronic systems.

Carbon nanotubes found safe for reconnecting damaged neurons

(credit: Polina Shuvaeva/iStock)

Multiwall carbon nanotubes (MWCNTs) could safely help repair damaged connections between neurons by serving as supporting scaffolds for growth or as connections between neurons.

That’s the conclusion of an in-vitro (lab) open-access study with cultured neurons (taken from the hippcampus of neonatal rats) by a multi-disciplinary team of scientists in Italy and Spain, published in the journal Nanomedicine: Nanotechnology, Biology, and Medicine.

A multi-walled carbon nanotube (credit: Eric Wieser/CC)

The study addressed whether MWCNTs that are interfaced to neurons affect synaptic transmission by modifying the lipid (fatty) cholesterol structure in artificial neural membranes.

Significantly, they found that MWCNTs:

  • Facilitate the full growth of neurons and the formation of new synapses. “This growth, however, is not indiscriminate and unlimited since, as we proved, after a few weeks, a physiological balance is attained.”
  • Do not interfere with the composition of lipids (cholesterol in particular), which make up the cellular membrane in neurons.
  • Do not interfere in the transmission of signals through synapses.

The researchers also noted that they recently reported (in an open access paper) low tissue reaction when multiwall carbon nanotubes were implanted in vivo (in live animals) to reconnect damaged spinal neurons.

The researchers say they proved that carbon nanotubes “perform excellently in terms of duration, adaptability and mechanical compatibility with tissue” and that “now we know that their interaction with biological material, too, is efficient. Based on this evidence, we are already studying an in vivo application, and preliminary results appear to be quite promising in terms of recovery of lost neurological functions.”

The research team comprised scientists from SISSA (International School for Advanced Studies), the University of Trieste, ELETTRA Sincrotrone, and two Spanish institutions, Basque Foundation for Science and CIC BiomaGUNE.


Abstract of Sculpting neurotransmission during synaptic development by 2D nanostructured interfaces

Carbon nanotube-based biomaterials critically contribute to the design of many prosthetic devices, with a particular impact in the development of bioelectronics components for novel neural interfaces. These nanomaterials combine excellent physical and chemical properties with peculiar nanostructured topography, thought to be crucial to their integration with neural tissue as long-term implants. The junction between carbon nanotubes and neural tissue can be particularly worthy of scientific attention and has been reported to significantly impact synapse construction in cultured neuronal networks. In this framework, the interaction of 2D carbon nanotube platforms with biological membranes is of paramount importance. Here we study carbon nanotube ability to interfere with lipid membrane structure and dynamics in cultured hippocampal neurons. While excluding that carbon nanotubes alter the homeostasis of neuronal membrane lipids, in particular cholesterol, we document in aged cultures an unprecedented functional integration between carbon nanotubes and the physiological maturation of the synaptic circuits.

Crystal ‘domain walls’ may lead to tinier electronic devices

Abstract art? No, nanoscale crystal sheets with moveable conductive “domain walls” that can modify a circuit’s electronic properties (credit: Queen’s University Belfast)

Queen’s University Belfast physicists have discovered a radical new way to modify the conductivity (ease of electron flow) of electronic circuits — reducing the size of future devices.

The two latest KurzweilAI articles on graphene cited faster/lower-power performance and device-compatibility features. This new research takes another approach: Altering the properties of a crystal to eliminate the need for multiple circuits in devices.

Reconfigurable nanocircuitry

To do that, the scientists used “ferroelectric copper-chlorine boracite” crystal sheets, which are almost as thin as graphene. The researchers discovered that squeezing the crystal sheets with a sharp needle at a precise location causes a jigsaw-puzzle-like pattern of “domains walls” to develop around the contact point.

Then, using external applied electric fields, these writable, erasable domain walls can be repeatedly moved around in the crystal to create a variety of new electronic properties. They can appear, disappear, or move around within the crystal, all without permanently altering the crystal itself.

Eliminating the need for multiple circuits may reduce the size of future computers and other devices, according to the researchers.

The team’s findings have been published in an open-access paper in Nature Communications.


Abstract of Injection and controlled motion of conducting domain walls in improper ferroelectric Cu-Cl boracite

Ferroelectric domain walls constitute a completely new class of sheet-like functional material. Moreover, since domain walls are generally writable, erasable and mobile, they could be useful in functionally agile devices: for example, creating and moving conducting walls could make or break electrical connections in new forms of reconfigurable nanocircuitry. However, significant challenges exist: site-specific injection and annihilation of planar walls, which show robust conductivity, has not been easy to achieve. Here, we report the observation, mechanical writing and controlled movement of charged conducting domain walls in the improper-ferroelectric Cu3B7O13Cl. Walls are straight, tens of microns long and exist as a consequence of elastic compatibility conditions between specific domain pairs. We show that site-specific injection of conducting walls of up to hundreds of microns in length can be achieved through locally applied point-stress and, once created, that they can be moved and repositioned using applied electric fields.

New chemical method could revolutionize graphene use in electronics

Adding a molecular structure containing carbon, chromium, and oxygen atoms retains graphene’s superior conductive properties. The metal atoms (silver, in this experiment) to be bonded are then added to the oxygen atoms on top. (credit: Songwei Che et al./Nano Letters)

University of Illinois at Chicago scientists have solved a fundamental problem that has held back the use of wonder material graphene in a wide variety of electronics applications.

When graphene is bonded (attached) to metal atoms (such as molybdenum) in devices such as solar cells, graphene’s superior conduction properties degrade.

The solution: Instead of adding molecules directly to the individual carbon atoms of graphene, the new method first adds a sort of buffer (consisting of chromium, carbon, and oxygen atoms) to the graphene, and then adds the metal atoms to this buffer material instead. That enables the graphene to retain its unique properties of electrical conduction.

In an experiment, the researchers successfully added silver nanoparticles to graphene with this method. That increased the material’s ability to boost the efficiency of graphene-based solar cells by 11 fold, said Vikas Berry, associate professor and department head of chemical engineering and senior author of a paper on the research, published in Nano Letters.

Researchers at Indian Institute of Technology and Clemson University were also involved in the study. The research was funded by the National Science Foundation.


Abstract of Retained Carrier-Mobility and Enhanced Plasmonic-Photovoltaics of Graphene via ring-centered η6 Functionalization and Nanointerfacing

Binding graphene with auxiliary nanoparticles for plasmonics, photovoltaics, and/or optoelectronics, while retaining the trigonal-planar bonding of sp2 hybridized carbons to maintain its carrier-mobility, has remained a challenge. The conventional nanoparticle-incorporation route for graphene is to create nucleation/attachment sites via “carbon-centered” covalent functionalization, which changes the local hybridization of carbon atoms from trigonal-planar sp2to tetrahedral sp3. This disrupts the lattice planarity of graphene, thus dramatically deteriorating its mobility and innate superior properties. Here, we show large-area, vapor-phase, “ring-centered” hexahapto (η6) functionalization of graphene to create nucleation-sites for silver nanoparticles (AgNPs) without disrupting its sp2 character. This is achieved by the grafting of chromium tricarbonyl [Cr(CO)3] with all six carbon atoms (sigma-bonding) in the benzenoid ring on graphene to form an (η6-graphene)Cr(CO)3 complex. This nondestructive functionalization preserves the lattice continuum with a retention in charge carrier mobility (9% increase at 10 K); with AgNPs attached on graphene/n-Si solar cells, we report an ∼11-fold plasmonic-enhancement in the power conversion efficiency (1.24%).

Graphene-based computer would be 1,000 times faster than silicon-based, use 100th the power

How a graphene-based transistor would work. A graphene nanoribbon (GNR) is created by unzipping (opening up) a portion of a carbon nanotube (CNT) (the flat area, shown with pink arrows above it). The GRN switching is controlled by two surrounding parallel CNTs. The magnitudes and relative directions of the control current, ICTRL (blue arrows) in the CNTs determine the rotation direction of the magnetic fields, B (green). The magnetic fields then control the GNR magnetization (based on the recent discovery of negative magnetoresistance), which causes the GNR to switch from resistive (no current) to conductive, resulting in current flow, IGNR (pink arrows) — in other words, causing the GNR to act as a transistor gate. The magnitude of the current flow through the GNR functions as the binary gate output — with binary 1 representing the current flow of the conductive state and binary 0 representing no current (the resistive state). (credit: Joseph S. Friedman et al./Nature Communications)

A future graphene-based transistor using spintronics could lead to tinier computers that are a thousand times faster and use a hundredth of the power of silicon-based computers.

The radical transistor concept, created by a team of researchers at Northwestern University, The University of Texas at Dallas, University of Illinois at Urbana-Champaign, and University of Central Florida, is explained this month in an open-access paper in the journal Nature Communications.

Transistors act as on and off switches. A series of transistors in different arrangements act as logic gates, allowing microprocessors to solve complex arithmetic and logic problems. But the speed of computer microprocessors that rely on silicon transistors has been relatively stagnant since around 2005, with clock speeds mostly in the 3 to 4 gigahertz range.

Clock speeds approaching the terahertz range

The researchers discovered that by applying a magnetic field to a graphene ribbon (created by unzipping a carbon nanotube), they could change the resistance of current flowing through the ribbon. The magnetic field — controlled by increasing or decreasing the current through adjacent carbon nanotubes — increased or decreased the flow of current.

A cascading series of graphene transistor-based logic circuits could produce a massive jump, with clock speeds approaching the terahertz range — a thousand times faster.* They would also be smaller and substantially more efficient, allowing device-makers to shrink technology and squeeze in more functionality, according to Ryan M. Gelfand, an assistant professor in The College of Optics & Photonics at the University of Central Florida.

The researchers hope to inspire the fabrication of these cascaded logic circuits to stimulate a future transformative generation of energy-efficient computing.

* Unlike other spintronic logic proposals, these new logic gates can be cascaded directly through the carbon materials without requiring intermediate circuits and amplification between gates. That would result in compact circuits with reduced area that are far more efficient than with CMOS switching, which is limited by charge transfer and accumulation from RLC (resistance-inductance-capacitance) interconnect delays.


Abstract of Cascaded spintronic logic with low-dimensional carbon

Remarkable breakthroughs have established the functionality of graphene and carbon nanotube transistors as replacements to silicon in conventional computing structures, and numerous spintronic logic gates have been presented. However, an efficient cascaded logic structure that exploits electron spin has not yet been demonstrated. In this work, we introduce and analyse a cascaded spintronic computing system composed solely of low-dimensional carbon materials. We propose a spintronic switch based on the recent discovery of negative magnetoresistance in graphene nanoribbons, and demonstrate its feasibility through tight-binding calculations of the band structure. Covalently connected carbon nanotubes create magnetic fields through graphene nanoribbons, cascading logic gates through incoherent spintronic switching. The exceptional material properties of carbon materials permit Terahertz operation and two orders of magnitude decrease in power-delay product compared to cutting-edge microprocessors. We hope to inspire the fabrication of these cascaded logic circuits to stimulate a transformative generation of energy-efficient computing.

New 3D printing method may allow for fast, low-cost, more-flexible medical implants for millions


UF Soft Matter | Silicone is 3D-printed into the micro-organogel support material. The printing nozzle follows a predefined trajectory, depositing liquid silicone in its wake. The liquid silicone is supported by the micro-organogel material during this printing process.

University of Florida (UF) researchers have developed a method for 3D printing soft-silicone medical implants that are stronger, quicker, less expensive, more flexible, and more comfortable than the implants currently available. That should be good news for the millions of people every year who need medical devices implanted.

Model 3D-printed silicone trachea implant (credit: University of Florida)

Currently, such devices — such as ports for draining bodily fluids (cerebral spinal fluid in hydrocephalus, for example), implantable bands, balloons, soft catheters, slings and meshes — are mass produced and made through molding processes. To create customized parts for individual patients with molding would be very expensive and could take days or weeks for each job.

The 3D printing method cuts that time to hours, potentially saving lives.

The ability to easily replace silicone implants at low cost is especially important for children, where “implants may need to be replaced frequently as they grow up,” Thomas E. Angelini, an associate professor of mechanical engineering  of the UF Department of Mechanical and Aerospace Engineering, explained to KurzweilAI. Angelini is senior author of a paper published May 10, 2017 in the open-access journal Science Advances.

The research could also pave the way for new therapeutic devices that encapsulate and control the release of drugs or small molecules for guiding tissue regeneration or assisting diseased organs, such as the pancreas or prostate, according to lead author Christopher O’Bryan, a UF mechanical and aerospace engineering doctoral student.


UF Soft Matter | Water is pumped from one reservoir to another using a 3D-printed silicone valve. The silicone valve contains two encapsulated ball valves that allow water to be pumped through the valve by squeezing the lower chamber. The silicone valve demonstrates the ability of the UF 3D-printing method to create multiple encapsulated components in a single part — something that cannot be done with a traditional 3D-printing approach.


Abstract of Self-assembled micro-organogels for 3D printing silicone structures

The widespread prevalence of commercial products made from microgels illustrates the immense practical value of harnessing the jamming transition; there are countless ways to use soft, solid materials that fluidize and become solid again with small variations in applied stress. The traditional routes of microgel synthesis produce materials that predominantly swell in aqueous solvents or, less often, in aggressive organic solvents, constraining ways that these exceptionally useful materials can be used. For example, aqueous microgels have been used as the foundation of three-dimensional (3D) bioprinting applications, yet the incompatibility of available microgels with nonpolar liquids, such as oils, limits their use in 3D printing with oil-based materials, such as silicone. We present a method to make micro-organogels swollen in mineral oil, using block copolymer self-assembly. The rheological properties of this micro-organogel material can be tuned, leveraging the jamming transition to facilitate its use in 3D printing of silicone structures. We find that the minimum printed feature size can be controlled by the yield stress of the micro-organogel medium, enabling the fabrication of numerous complex silicone structures, including branched perfusable networks and functional fluid pumps.