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A nanoelectrode array and its CMOS control chip sit at the bottom of a shallow well where a network of cells will grow.

Nanoelectrode Array Sees Signals From Inside a Network of Cells

Researchers at Harvard University have developed a nanoelectrode array capable of imaging the electrical signals within the living cells. While other technologies have been able to measure these signals, this new complimentary metal oxide semiconductor nanoelectrode array (called a CNEA) can measure these signal across an entire network of cells.

“It’s similar to an imager combining the light signal from each detector in a pixel array to form a picture; the CNEA combines the electrical signals from within each cell to map the network level electrical activities of the entire cell culture,” explained Donhee Ham, a professor at Harvard involved in the research, in an e-mail interview with IEEE Spectrum.

This network-level intracellular recording capability can be used, for example, to examine the effect of pharmaceuticals on a network of heart muscle tissue, enabling tissue-based screening of drug candidates. It could also help better understand how cells communicate with each other across a network.

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A laser stylus writes on a small array of multifunction pixels made by dual-function LEDs than can both emit and respond to light.

Nanorods Emit and Detect Light, Could Lead to Displays That Communicate via Li-Fi

Ever since the 2015 Consumer Electronics Show, quantum dots have been in a market struggle to displace light-emitting diodes (LEDs) as a backlight source for liquid crystal displays (LCDs).

Now an advance by a team of researchers from the University of Illinois at Urbana–Champaign, the Electronics and Telecommunications Research Institute in South Korea, and Dow Chemical may turn the display market on its head by eliminating the need for backlights in LCD devices. They have produced a LED pixel out of nanorods capable of both emitting and detecting light.

In the video below, you can get a further description of how the nanorods manage to both detect and emit light as well as some pretty attractive future applications, like mobile phones that can “see” without the need of a camera lens or communicate with each other using Light Fidelity (Li-Fi) technology.

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Top view of the experimental set-up used in the paper.

Scientists Measure Single Quantum of Heat

IBM researchers have established experimental proof of a previously difficult-to-prove law of physics, and in so doing may have pointed to a way to overcome many of the heat management issues faced in today’s electronics. Researchers at IBM Zurich have been able to take measurements of the thermal conductance of metallic quantum point contacts made of gold. No big deal, you say? They conducted measurements at the single-atom level, at room temperature—the first time that’s ever been done.

The first measurement of a quantum of thermal conductance was achieved back in 1999 by researchers at the California Institute of Technology. This latest research differs in that it was able to make measurements at room temperature as opposed to very low temperatures.

These latest measurements provide further confirmation of the Wiedemann–Franz law, which predicts that the smallest amount of heat that can be carried across a metallic junction—a single quantum of heat—is directly proportional to the quantum of electrical conductance through the same junction. By experimentally confirming this law, it can now be used with confidence to predict and to explore nanoscale thermal and electrical phenomena affecting materials down to the size of few atoms or a single molecule.

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image of a device with lateral pads patterned as electrically connected finger-like structures

Graphene Infrared Eye Needs No Signal Amplification

An international team of researchers under the umbrella of the EU-funded Graphene Flagship have taken a significant step in thermal infrared (IR) photodetctors with the development of the most sensitive uncooled graphene-based thermal detector yet fabricated.  These new photodetectors, known as bolometers, are so sensitive that they can register the presence of a scant few nanowatts of radiation. That level of radiation is about a thousandth of what would be given off by a hand waving in front of the detector.

In the research described in the journal Nature Communications, scientists from the University of Cambridge, UK; the Institute of Photonic Sciences (ICFO), Spain; the University of Ioannina, Greece; and from Nokia and Emberion found that the combination of graphene and pyroelectric materials—which generate a voltage when they are heated or cooled—yields a unique synergy that boosts the performance of thermal photodetectors.

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water-based two-dimensional crystal inks

Biocompatible Inks for Printed Medical Devices Just Got Easier to Make

Researchers at the University of Manchester in the UK have built photosensors and programmable logic memory devices with inkjet printers using biocompatible, water-based 2D crystal inks that are highly concentrated for improved electrical performance.

The Manchester research, described in the journal Nature Nanotechnology,  represents a significant development over current ink formulations that are typically toxic and difficult to process. While this new formulation is easier to produce, biocompatibility may be its most attractive feature, opening up potential applications in medical devices.

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Smoltek's chip packaging process

Nanomaterials Enable Smaller Chip Packaging

Overwhelmingly, the focus for applying nanomaterials to electronics has been to meet the demands of Moore’s Law by continuing the seemingly inexorable shrinking of transistor dimensions.

While there have been some remarkable achievements in that regard—among them, getting dimensions down as low as 1 nanometer in the laboratory—the drive towards putting systems on chips (SoC) and systems in packages (SiP) is causing a shift in focus from smaller transistors to smaller packaging. This shift appears to be opening up a new use for nanomaterials that could expand the focus of nanomaterials in chip manufacturing.

The Swedish company Smoltek AB, a spinout from Chalmers University, sees chip packaging as the new frontier in nanoelectronics. It has been positioning itself at the forefront of this new movement over the last five years with its development of a variation on chemical vapor deposition (CVD) technology it has dubbed SMOLTEK TigerTM.

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Nantero NRAM nonvolatile memory chip

Carbon Nanotube Memory Company's Ship May Finally Come In

To many, the sell-by date on the carbon nanotube-based non-volatile random access memory (NRAM) developed by Nantero has long since passed. IEEE Spectrum characterized the technology as a “loser” nearly a decade ago after several of the company’s launch dates came and went with hardly a whimper.

The technology’s promise was that it could lend itself to easy mass production because it relies on a group of nanotubes deposited randomly on a substrate rather than individual nanotubes precisely placed. By eliminating the need for individual placement, Nantero hoped to sidestep the main bugbear of nanotubes in electronics: purity. It turns out purity could not be sidestepped to the degree originally believed, and a decade-and-half of disappointment ensued.

But a new analyst report published by BCC Research asserts that NRAM’s ship may have finally come in. The upshot: It (and a host of other non-volatile memory approaches) may be poised to dislodge flash from its long-held throne.

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Schematic diagram showing the structure of a carbon nanotube transistor

Scientists: Carbon Nanotubes Would Outperform Silicon Transistors at the Same Scale

The end appears nigh for scaling down silicon-based complementary metal-oxide semiconductor (CMOS) transistors, with some experts seeing the cutoff date as early as 2020

While carbon nanotubes (CNTs) have long been among the nanomaterials investigated to serve as replacement for silicon in CMOS field-effect transistors (FETs) in a postsilicon future, they have always been bogged down by some frustrating technical problems. But, with some of the main technical showstoppers having been largely addressed—like sorting between metallic and semiconducting carbon nanotubes—the stage has been set for CNTs to start making their presence felt a bit more urgently in the chip industry.

Peking University scientists in China have now developed carbon-nanotube field-effect transistors (CNT FETs) having a critical dimension—the gate length of just 5 nanometers—that would outperform silicon-based CMOS FETs at the same scale. The researchers claim in the journal Science that this marks the first time that carbon-nanotube CMOS FETs under 10 nanometers have been reported.

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Super-thin graphene-based health monitor is mechanically invisible

Graphene Temporary Tattoo Tracks Vital Signs

A graphene health sensor that goes on the skin like a temporary tattoo takes measurements with the same precision as bulky medical equipment. The graphene tattoos, presented in December at the International Electron Devices Meeting in San Francisco, are the thinnest epidermal electronics ever made. They can measure electrical signals from the heart, muscles, and brain, as well as skin temperature and hydration.

Researchers at the University of Texas at Austin who are developing the sensors hope to develop them for consumer cosmetic use. They also hope the ultrathin sensors will provide a more comfortable replacement for existing medical equipment.

Today, if your doctor wants to monitor your heart rate over an extended period of time to help diagnose some cardiac irregularity, you’ll be sent home with a bulky EKG monitoring harness to wear for 24 hours. The Texas researchers hope to make a system that can take measurements of the same quality or better, but that’s unobtrusive. Deji Akinwande, an electrical engineer who specializes in 2D materials, is collaborating on the project with Nanshu Lu, who works on epidermal electronics.

Materials scientists have for years sung the praises of graphene’s electrical properties and mechanical toughness. What’s been underappreciated, says Akinwande, is that this single-atom-thick stuff is mechanically invisible. When it goes on the skin, it doesn’t just stay flat—it conforms to the microscale ridges and roughness of the epidermis. “You don’t feel it because it’s so compliant,” says Akinwande.

The Texas researchers start by growing single-layer graphene on a sheet of copper. The 2D carbon sheet is then coated with a stretchy support polymer, and the copper is etched off. Next, the polymer-graphene sheet is placed on temporary tattoo paper, the graphene is carved to make electrodes with stretchy spiral-shaped connections between them, and the excess graphene is removed. Now the sensor is ready to be applied by placing it on the skin and wetting the back of the paper.

In their proof-of-concept work, the researchers used the graphene tattoos to take five kinds of measurements, and compared the data with results from conventional sensors. The graphene electrodes can pick up changes in electrical resistance caused by electrical activity in the tissue underneath. When worn on the chest, the graphene sensor detected faint fluctuations that were not visible on an EKG taken by an adjacent, conventional electrode. The sensor readouts for electroencephalography (EEG) and electromyography (EMG, which can be used to register electrical signals from muscles and is being incorporated into next-generation prosthetic arms and legs) were also of good quality. And the sensors could measure skin temperature and hydration, something cosmetics companies are interested in, says Akinwande.

Graphene’s conformity to the skin might be what enables the high-quality measurements. Air gaps between the skin and the relatively large, rigid electrodes used in conventional medical devices degrade these instruments’ signal quality. Newer sensors that stick to the skin and stretch and wrinkle with it have fewer airgaps, but because they’re still a few micrometers thick, and use gold electrodes hundreds of nanometers thick, they can lose contact with the skin when it wrinkles. The graphene in the Texas researchers’ device is 0.3-nm thick. Most of the tattoo’s bulk comes from the 463-nm-thick polymer support.

The next step is to add an antenna to the design so that signals can be beamed off the device to a phone or computer, says Akinwande.

Black and white microscope image of molybdenum disulfide transistors shows vertical bars at top crossing a horizontal bar and vertical bars at bottom intersecting the spaces between them.

Molybdenum-Disulfide 2D Transistors Go Ballistic

Molybdenum disulfide, a two dimensional semiconductor that’s just 3 atoms thick, has had a big year. In October, a group of researchers made a 1-nanometer transistor from the material, showing that even if silicon transistors stop shrinking, the new material might provide a path forward. In December, at the IEEE International Electron Devices Meeting in San Francisco, researchers presented work they say shows that molybdenum disulfide not only makes for superlative single transistors, but can be made into complex circuits using realistic manufacturing methods.

At the meeting, a group from Stanford showed that transistors made from large sheets of MoS2 can be used to make transistors with 10-nanometer-long, gate having electronic properties that approach the material’s theoretical limits. The devices displayed traits close to ballistic conduction, a state of very low electrical resistance that allows the unimpeded flow of charge over relatively long distances—a phenomenon that should lead to speedy circuits. Separately, a team from MIT demonstrated complex circuit elements made from MoS2 transistors.

Most of the work on molybdenum disulfide so far has been what Stanford electrical engineer Eric Pop calls “Powerpoint devices.” These one-off devices, made by hand in the lab, have terrific performance that looks great in a slide. This step is an important one, says Pop, but the 2D material is now maturing.

The Stanford lab’s transistors are not as small as the record-breaking ones demonstrated in October. What’s significant, says group leader Pop, is that these latest transistors maintained similar performance even though they were made using more industrial-type techniques. Instead of using Scotch tape to peel off a layer of molybdenum disulfide from a rock of the material, then carefully placing it down and crafting one transistor at a time, Pop’s grad student started by growing a large sheet of the material on a wafer of silicon.

In a transistor, a gate electrode switches the semiconductor channel between conducting and insulating states. In the Stanford device, the tricky part was coming up with an easy way to make a small gate atop the molybdenum disulfide without harming it, says Pop. That is, until his student, Christopher English, realized they could harness the power of rust. English chose a somewhat unusual material, aluminum, to serve as the gate electrode. He deposited a 20-nanometer finger of aluminum on the molybdenum, then allowed it to oxidize and shrink down to a smaller size. The gate ends up being about 10 nanometers.

At these relatively small dimensions, the molybdenum disulfide transistors approach their ultimate electrical limit, a state called ballistic conduction. When a device is small enough (or at low enough temperature), electrons will travel through the conducting medium without scattering because of collisions with the atoms that make up the material. Transistors operating ballistically should switch very fast and enable high-performance processors. Pop estimates that about 1 in 5 electrons moves though the rusty transistors ballistically. By further improving the quality of the material (or making the transistors smaller), he expects that ratio to improve. The important thing, he says, is the way they achieved this: using methods that could translate to larger scales. “We have all the ingredients we need to scale this up,” says Pop.

Zippy nanoscale transistors are great on their own, but they’re useful only if you can build them into circuits.  Researchers from MIT demonstrated just that by constructing working registers and latches. They managed the feat, says electrical engineer Dina El-Damak, by creating computer-aided design software tailored to MoS2. This sort of software is common in the silicon world and enables designers to come up with new circuits relatively easily. (El-Damak worked on the molybdenum disulfide project at MIT and is now a professor at the University of Southern California in Los Angeles.)

Since molybdenum disulfide is so new, not many circuit designers have worked with the material. So far, most work has been done by trial and error, one device at a time. The MIT group can create an informed circuit design, using their computer models to simulate the best and worst cases, based on the material’s known properties and the performance of previous devices, says El-Damak. Then the group fabricates the design that seems most likely to work, tests its performance, and feeds the results back into the program. “By doing this, we have more confidence in scaling up this technology,” she says.

Both Pop and El-Damak say molybdenum disulfide is unlikely to be a direct replacement for silicon. The material will either be used to build complementary systems on top of silicon chips, or it will be used on its own in flexible, transparent electronics. It’s also possible that some other 2D semiconductor will end up being a better option. Molybdenum disulfide is a few steps ahead because researchers have worked with it more than, say, tungsten selenide, and know how to grow the material over large areas.

The Stanford and MIT research demonstrates important progress in this field, says Deji Akinwande, an electrical engineer at the University of Texas at Austin who co-chaired the IEDM session on 1D and 2D devices. People who work in industry are always asking when these materials will be made into useful circuits, and now it’s happening, he says. “Industry is starting to take this more seriously, now that it’s no longer just the grad student in the basement working on it,” he says.

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Nanoclast

IEEE Spectrum’s nanotechnology blog, featuring news and analysis about the development, applications, and future of science and technology at the nanoscale.

 
Editor
Dexter Johnson
Madrid, Spain
Contributor
Rachel Courtland
New York City
 
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