Showing posts with label nanowire. Show all posts
Showing posts with label nanowire. Show all posts

February 06, 2014

Nanowire nanocomputer as a finite-state machine

PNAS - Nanowire nanocomputer as a finite-state machine Fundamental limits soon may end the decades-long trend in microelectronic computer circuit miniaturization that has led to much technological and economic progress. Nanoelectronic circuits using new materials, devices, and/or fabrication methods face formidable challenges to provide alternatives for future microelectronics. A key advance toward overcoming these hurdles is achieved in this work through the construction of a nanoelectronic finite-state machine (nanoFSM) computer using “bottom–up” methods. The nanoFSM integrates both computing and memory elements, which are organized from individually addressable and functionally identical nanodevices, to perform clocked, multistage logic. Furthermore, the device density is the highest reported to date for any nanoelectronic system. Advances in logic and design in the nanoFSM are scalable and should enable more extensive nanocomputers.

IEEE Spectrum summarises the work -

Researchers have arranged a total of 180 such transistor nodes in six crossbar arrays and divided them into three separate tiles to make a finite-state machine capable of performing arithmetical operations. In one configuration, the first tile does the math, while the second tile holds one bit in memory and the third tile holds a second bit. Chemist Charles Lieber, head of the Harvard team, says more tiles can be added in a Lego-like fashion. The version the team built was a two-bit adder. Four tiles would make a four-bit adder, and so on. A four-by-four array of tiles “could function as a pretty sophisticated microprocessor,” he says.

Lieber says the nanowire device will likely surpass CMOS chips only in very specific applications that benefit from low power consumption and operate at megahertz rather than gigahertz clock rates. But Ellenbogen hopes the research will provide hints for where CMOS technology can be improved. “We think some of the approaches are more generally applicable,” he says.

Fabricated nanoelectronic chip. (A) SEM image of the final chip (scale bar, 500 μm). (B) SEM image of the inner layout of the fabricated chip as indicated in the dashed box in A. The red dashed box region corresponds to the chip’s basic three-tile circuit shown. (Scale bar, 100 μm.) (Credit: Jun Yao et al./PNAS)

Full 10 page pdf

MITRE and Harvard have a press release on their nanowire computer.

May 09, 2013

Nanowire Gate All Around Transistors

Gate-All-Around Transistors: In a new design, the transistor channel is made up of an array of vertical nanowires. The gate surrounds all the nanowires, which improves its ability to control the flow of current. Platinum-based source and drain contacts sit at the top and bottom of the nanowires.

Engineers may already have come up with the technology that will fend off the Moore Law is doomed skeptics: nanowire FETs (field-effect transistors).

In these nanodevices, current flows through the nanowire or is pinched off under the control of the voltage on the gate electrode, which surrounds the nanowire. Hence, nanowire FETs’ other name: “gate-all-around” transistors. However, because of their small size, single nanowires can’t carry enough current to make an efficient transistor.

The solution, recent research shows, is to make a transistor that consists of a small forest of nanowires that are under the control of the same gate and so act as a single transistor. For example, researchers at Hokkaido University and from the Japan Science and Technology Agency reported last year in Nature a gate-all-around nanowire transistor consisting of 10 vertical indium gallium arsenide nanowires grown on a silicon substrate. Although the device’s electrical properties were good, the gate length—a critical dimension—was 200 nanometers, much too large for the tiny transistors needed to power the microprocessors of the 2020s. 

Now two researchers working in France, Guilhem Larrieu of the Laboratory for Analysis and Architecture of Systems, in Toulouse, and Xiang‑Lei Han of the Institute for Electronics, Microelectronics, and Nanotechnology, in Lille, report the creation of a nanowire transistor that could be scaled down to do the job. It consists of an array of 225 doped-silicon nanowires, each 30 nm wide and 200 nm tall, vertically linking the two platinum contact planes that form the source and drain of the transistor. Besides their narrowness, what’s new is the gate: A single 14-nm-thick chromium layer surrounds each nanowire midway up its length. 

Vertical nanowire array-based field effect transistors for ultimate scaling

April 10, 2013

Laser Camera using superconducting nanowires takes 3-D Images From 1000 meters away

Using superconducting nanowires and lasers, a new camera system can produce high-resolution 3-D images of objects from up to a kilometer away.

The technology works by sending out a low-power infrared laser beam, which sweeps over an object or scene. Some light gets reflected back, though most is scattered in different directions. A detector measures how long it takes one particle of light, a photon, to return to the camera and is then able to calculate the distance from the system to the object. The technique can resolve millimeter-size bumps and changes in depth from hundreds of meters away.

The new camera takes advantage of superconducting nanowires, materials with almost no electrical resistance that have to be cooled to extremely low temperatures. These superconductors are very sensitive and can tell when just a single photon has hit them.

Although other approaches can have exceptional depth resolution, the ability of the new system to image objects like items of clothing that do not easily reflect laser pulses makes it useful in a wider variety of field situations

Pictures on the right were from 910 meters away

Optical Society - New camera system creates high-resolution 3-D images from up to a kilometer away

March 25, 2013

Nanowires are improving quantum dot solar cell efficiency towards minimum commercial viability

Using exotic particles called quantum dots as the basis for a photovoltaic cell is not a new idea, but attempts to make such devices have not yet achieved sufficiently high efficiency in converting sunlight to power.

Zinc Oxide nanowires are conductive enough to extract charges easily, but long enough to provide the depth needed for light absorption. Using a bottom-up growth process to grow these nanowires and infiltrating them with lead-sulfide quantum dots produces a 50 percent boost in the current generated by the solar cell, and a 35 percent increase in overall efficiency, Jean says. The process produces a vertical array of these nanowires, which are transparent to visible light, interspersed with quantum dots.

Already, the test devices have produced efficiencies of almost 5 percent, among the highest ever reported for a quantum-dot PV based on zinc oxide. With further development, it may be possible to improve the devices’ overall efficiency beyond 10 percent, which is widely accepted as the minimum efficiency for a commercially viable solar cell. Further research will, among other things, explore using longer nanowires to make thicker films, and also work on better controlling the spacing of the nanowires to improve the infiltration of quantum dots between them.

Scanning Electron Microscope images show an array of zinc-oxide nanowires (top) and a cross-section of a photovoltaic cell made from the nano wires, interspersed with quantum dots made of lead sulfide (dark areas). A layer of gold at the top (light band) and a layer of indium-tin-oxide at the bottom (lighter area) form the two electrodes of the solar cell.
Images courtesy of Jean, Advanced Materials

February 26, 2013

Hole Spin Quantum Dots Brings us closer to new high-speed quantum computers

A new method preserves spin qubits up to ten times longer. Hole spins, rather than electron spins, can keep quantum bits in the same physical state up to 10 times longer than before.

The holes within hole spins, Frolov explained, are literally empty spaces left when electrons are taken out. Using extremely thin filaments called InSb (indium antimonide) nanowires, the researchers created a transistor-like device that could transform the electrons into holes. They then precisely placed one hole in a nanoscale box called “a quantum dot” and controlled the spin of that hole using electric fields. This approach— featuring nanoscale size and a higher density of devices on an electronic chip—is far more advantageous than magnetic control, which has been typically employed until now, said Frolov.

“Our research shows that holes, or empty spaces, can make better spin qubits than electrons for future quantum computers.”

“Spins are the smallest magnets in our universe. Our vision for a quantum computer is to connect thousands of spins, and now we know how to control a single spin,” said Frolov. “In the future, we’d like to scale up this concept to include multiple qubits.”

Nature Nanotechnology - Electrical control of single hole spins in nanowire quantum dots

Arxiv - Electrical control over single hole spins in nanowire quantum dots

October 16, 2012

Nanowire solar cells could theoretically convert 60% of power and have a practical target of 38%

Bandgap Engineering's nanowire-enhanced solar cell designs combine low-cost processing with crystalline silicon to yield high-efficiency products. Our highly tunable silicon nanowires make these designs possible, leading to solar power cost-competitive with the grid.

Technology Review - The nanowire-based solar cell could eventually generate twice as much power as conventional solar cells.

That's a long-term project, but meanwhile the company is about to start selling a simpler version of the technology, using silicon nanowires that can improve the performance and lower the cost of conventional silicon solar cells. Bandgap says its nanowires, which can be built using existing manufacturing tools, boost the power output of solar cells by increasing the amount of light the cells can absorb.

Right now most solar-panel manufacturers aren't building new factories because the market for their product is glutted. But if market conditions improve and manufacturers do start building, they'll be able to introduce larger changes to production lines. In that case the Bandgap technology could make it possible to change solar cells more significantly. For example, by increasing light absorption, it could allow manufacturers to use far thinner wafers of silicon, reducing the largest part of a solar cell's cost. It could also enable manufacturers to use copper wires instead of more expensive silver wires to collect charge from the solar panels.

These changes could lead to solar panels that convert over 20 percent of the energy in sunlight into electricity (compared with about 15 percent for most solar cells now) yet cost only $1 per watt to produce and install, says Richard Chleboski, Bandgap's CEO.

September 14, 2012

Norway scientists commercialize semiconductors grown on graphene

Norwegian University of Science and Technology (NTNU) researchers report they have patented and are commercializing gallium arsenide (GaAs) nanowires grown on graphene, a hybrid material with competitive properties. Semiconductors grown on graphene are expected to become the basis for new types of device systems, and could fundamentally change the semiconductor industry.

Crayonano is the caompny commercializing the work.

The new patented hybrid material offers excellent optoelectronic properties, says Professor Helge Weman, a professor at NTNU's Department of Electronics and Telecommunications, and CTO and co-founder of the company created to commercialize the research, CrayoNano AS. "We have managed to combine low cost, transparency and flexibility in our new electrode," he adds.

The patented method of growing semiconductor nanowires on atomically thin graphene uses molecular beam epitaxy (MBE) to grow the nanowires.

"We do not see this as a new product," Weman says. "This is a template for a new production method for semiconductor devices. We expect solar cells and light emitting diodes to be first in line when future applications are planned."

Nanoletters - Vertically Aligned GaAs Nanowires on Graphite and Few-Layer Graphene: Generic Model and Epitaxial Growth

June 12, 2012

1 nanometer diameter wires could yield next gen quantum computers

New Electronics UK - Nanowires can now be made with a diameter of just 1 nanometer (nm), though researchers tend to work with nanowires that are between 30 and 60nm wide. At these dimensions, materials can acquire properties very different to those they exhibit at larger scales. That is partly because at such tiny scales, quantum confinement effects alter the behaviour of fundamental particles like electrons within the material. Such effects can change how materials conduct electricity and heat, or interact with light.

"There are a host of niche applications within the electronics sector, such as solar cells and sensors, where nanowires could have a significant impact in the medium term and rapid advances are being made. You could say nanowires have taken on some of the attention that a few years ago was being spent on nanotubes."

A key question about nanowires concerns how best to manufacture them: building them from the bottom up, or from the top down? A top down approach involves taking the material that will form the nanowire and reducing it until you reach nanoscale dimensions. As its name suggests, the bottom up approach is an assembly process where the nanowire is 'grown', by adding particles gradually.

May 14, 2012

Graphene and Carbon nanotubes faster computers and better mobile phones

Graphene and carbon nanotubes could improve the electronics used in computers and mobile phones, reveals new research from the University of Gothenburg, Sweden.

Carbon nanotubes and graphene are both made up of carbon and have unique properties. Graphene comprises an atom-thick layer of carbon atoms, while carbon nanotubes can be likened to a graphene sheet that has been rolled up to form a tube.

"If you stretch a graphene sheet from end to end the thin layer can oscillate at a basic frequency of getting on for a billion times a second," says researcher Anders Nordenfelt. "This is the same frequency range used by radios, mobile phones and computers."

Self Oscillations and Cooling of Carbon Based NEMS Devices (73 page thesis)

May 03, 2012

Next-Generation Nanoelectronics - Nanoelectromechanical (NEM) switches

Silicon-based circuits continue to shrink in size in the relentless pursuit of Moore’s Law — the prediction that the number of transistors that can fit on an integrated circuit doubles every two years — power consumption is rising rapidly. In addition, conventional silicon electronics do not function well in extreme environments such as high temperatures or radiation.

In an effort to sustain the advance of these devices while curbing power consumption, diverse research communities are looking for hybrid or alternative technologies. Nanoelectromechanical (NEM) switch technology is one option that shows great promise.

“NEM switches consist of a nanostructure (such as a carbon nanotube or nanowire) that deflects mechanically under electrostatic forces to make or break contact with an electrode,” said Horacio Espinosa, James N. and Nancy J. Farley Professor in Manufacturing and Entrepreneurship at the McCormick School of Engineering at Northwestern University.

NEM switches, which can be designed to function like a silicon transistor, could be used either in standalone or hybrid NEM-silicon devices. They offer both ultra-low power consumption and a strong tolerance of high temperatures and radiation exposure.

Given their potential, the past decade has seen significant attention to the development of both hybrid and standalone NEM devices.
Comparing the performance of NEM technology with CMOS and other emerging technologies.

Nature Nanotechnology - Nanoelectromechanical contact switches

April 20, 2012

Majorana Fermion particle may have been discovered and it could explain Dark Matter and enable quantum computers

Scientists at TU Delft's Kavli Institute and the Foundation for Fundamental Research on Matter (FOM Foundation) have succeeded for the first time in detecting a Majorana particle. In the 1930s, the brilliant Italian physicist Ettore Majorana deduced from quantum theory the possibility of the existence of a very special particle, a particle that is its own anti-particle: the Majorana fermion. That 'Majorana' would be right on the border between matter and anti-matter.

Other researchers believe that more evidence needs to be produced to confirm the results.

Quantum computer and dark matter
Majorana fermions are very interesting – not only because their discovery opens up a new and uncharted chapter of fundamental physics; they may also play a role in cosmology. A proposed theory assumes that the mysterious 'dark matter, which forms the greatest part of the universe, is composed of Majorana fermions. Furthermore, scientists view the particles as fundamental building blocks for the quantum computer. Such a computer is far more powerful than the best supercomputer, but only exists in theory so far. Contrary to an 'ordinary' quantum computer, a quantum computer based on Majorana fermions is exceptionally stable and barely sensitive to external influences.

For the first time, scientists in Leo Kouwenhoven's research group managed to create a nanoscale electronic device in which a pair of Majorana fermions 'appear' at either end of a nanowire. They did this by combining an extremely small nanowire, made by colleagues from Eindhoven University of Technology, with a superconducting material and a strong magnetic field. 'The measurements of the particle at the ends of the nanowire cannot otherwise be explained than through the presence of a pair of Majorana fermions', says Leo Kouwenhoven.

Other say more evidence is needed before the claim of Majorana Fermions can be confimed

Journal Science - Signatures of Majorana Fermions in Hybrid Superconductor-Semiconductor Nanowire Devices

Majorana fermions are particles identical to their own antiparticles. They have been theoretically predicted to exist in topological superconductors. We report electrical measurements on InSb nanowires contacted with one normal (Au) and one superconducting electrode (NbTiN). Gate voltages vary electron density and define a tunnel barrier between normal and superconducting contacts. In the presence of magnetic fields of order 100 mT, we observe bound, mid-gap states at zero bias voltage. These bound states remain fixed to zero bias even when magnetic fields and gate voltages are changed over considerable ranges. Our observations support the hypothesis of Majorana fermions in nanowires coupled to superconductors.

Kouwenhoven’s team hopes to use a scheme called “topological quantum computation” that could evade decoherence at the hardware level by storing quantum information non-locally.