Sometimes I step onto a research result that is so incredible to make me think that it couldn’t have been imagined by science fiction and this is one of such cases.

The electron spins in a magnetic vortex all point in parallel, either clockwise or counterclockwise. Spins in the crowded core of the vortex must point out of the plane, either up or down. The four orientations of circularity and polarity could form the cells of multibit magnetic storage and processing systems. Credits: Berkeley Labs

Researchers at the Berkeley Lab are investigating ways of exploiting whirlpools at the nanoscale to create devices that can perform 100 times better than current ones in terms of power consumption and storage density.

Magnetic memory are based on the spin of the electrons. When you align the spin of many electrons in a specific area you get a magnetic field, by changing their spin you change the magnetic field and this is what is being used to store bits in a magnetic memory. All atoms have electrons and certain kind of atoms (the so called ferromagnetic materials) are easier to influence and therefore one can set their spin as desired (using a magnetic field).

What Berkeley Lab researchers did was to create a nanometric structure where the electromagnetic field creates a nanometric whirlpools having peculiar magnetic properties.

As shown in the figure on the left you can imagine having a disk 20 nm thick and 100 nm across spinning in one or the other direction. It is just for the sake of imagination, actually there is not such a disk but only a material made of atoms clustered in such a way that electrons rotate that way. Additionally, electrons have a spin (up or down)  that generates a magnetic field (-+).

The material is structured in such a way to generate whirlpools of magnetic field that can therefore have four different states, (+, -, clockwise, counterclockwise). Since it can have four states one can store 2 bits.

The researchers have found the way to create such structure and to use magnetic pulses to “write” a specific state (and then to “read” it).  The first structure was bigger, 30 nm thick and a thousand nm across, and although it worked the switching time from one state to the other was too long (relatively speaking…. since it took 3 ns!). By decreasing the size they have achieved a switching speed of half a ns (in that time frame a light ray moves 1.5 cm).

The problem researchers are still facing is that so far they have been able to sea between up and down spin or clockwise and counterclockwise but are not able to swap both at the same time. It would be like saying that you can write a 3 if you have a 1 or you can write a 2 if you have a 0 but you cannot write a 3 if you have a 0…. Obviously that is not good!

However, they feel that it will be just a matter of few more tweakings and a complete manipulation of the whirlpools will become possible.

We are, clearly, at the forefront of science, its practical application is not in sight but the discovery of these whirlpools, their properties, how to create them and how to exploit them identifies a possible path of evolution and usually that is what you need to stimulate innovation.

Insulating states and superlattice minibands in a graphene/hBN heterostructure. Schematic of the moiré pattern for graphene (gray) on hBN (red and blue), for zero misalignment angle and an exaggerated lattice mismatch of ~10%. The moiré unit cell is outlined in green. Regions of local quasi-epitaxial alignment lead to opposite signs of the sublattice asymmetry, m(r), in different regions. (Credit: B. Hunt et al./Science)

The 10 year European flagship project to make graphene the platform for the next decade electronics has just started but scientists all over the world are busy trying to turn graphene into an industrial material.

It has been know, since the last decade, that carbon nanotubes can be used as transistors by including certain kinds of atoms in the middle of the “tube”, creating a Schottky junction, that is the basic building block to create a transistor. Graphene is made of carbon atoms, like a carbon nanotube, but the atoms are placed on a plane, one atom thick. Hence one has to find another way to create a conductor-semiconductor junction, what is also known as a band gap.

Now researchers at the MIT have demonstrated a way to create such a band gap.

What they did was to overlay on the one atom thick layer of graphene another one atom thick layer of boron nitride. Both graphene and boron nitride have an hexagonal structure, as shown in the figure on the left. It is like having a quilt made of hexagon, the graphene layer conducting electrons and the boron nitride acting as an insulator.

The hexagon formed by the boron nitride are 1.8% larger than the ones formed by the graphene and it is therefore impossible to have a perfect alignment of the two structures. If you centre one hexagon of boron nitride on another of graphene in one point they are bound to be out of alignment just few rings away and therefore they lose the properties of creating a band gap.

Per sè this is not a stumbling block. It means that you have a perfect band gap every 50 rings or so and those are the places where transistors can be created. It is, of course, far more complicated because it would require an “atomic” precision to place a transistor exactly where it has to be placed… Still, it is a first step towards an industrial manufacturing of graphene based transistors.

Researchers have discovered another property that emerges from this overlaying of the two layers of boron nitride and graphene. Basically what happens is that by rotating one layer, hence changing the geometry of the juxtaposition of the rings, one changes the characteristics of the resulting band gap and hence of the resulting transistors.

One can imagine to have a variety of transistors on the two layers of different types, each type having a specific characteristics. We might end up discovering a way to use to our benefit the difference in size between boron nitride and graphene rings. What at first glance looked like a problem may become a bonus creating transistors “a la carte”.

The world of nano keeps surprising us with more and more unexpected twists…

Arrays of tree-like nanowires consisting of Si trunks and TiO2 branches facilitate solar water-splitting in a fully integrated artificial photosynthesis system (credit: Chong Liu et al./Lawrence Berkeley National Laboratory)

All around us we see a continuous transformation of energy coming from the Sun into chemical energy and most life on Earth is dependent on that: it is the photosynthesis carried out by all plants.

Chloroplasts, contained in leaves, absorb photons and generate high energy electrons that in turns activate a set of reactions leading to the formation of sugar. In the process CO2 is absorbed from the atmosphere hence decreasing the level of CO2 in the environment, quite the opposite of most others energy transformation that are actually producing CO2.

Now scientists at the Lawrence Berkeley National Laboratories have announced the invention of an artificial leaf, or, rather, an artificial forest.

Using nanotechnology they have managed to create an artificial photosynthetic system combining two semiconductor light absorbers, an interfacial layer for charge transport, and co-catalysts to spatially separate them.

You can see the result in the photo on the left.

Peidong Yang, a chemist with Berkeley Lab’s Materials Sciences Division, who led this research reports:

To facilitate solar water- splitting in our system, we synthesized tree-like nanowire  heterostructures, consisting of silicon trunks and titanium oxide branches. Visually, arrays of these nanostructures very much resemble an artificial forest.

In natural photosynthesis, the energy of absorbed sunlight produces energized charge-carriers that execute chemical reactions in separate regions of the chloroplast. We’ve integrated our nanowire nanoscale heterostructure into a functional system that mimics the integration in chloroplasts and provides a conceptual blueprint for better solar-to-fuel conversion efficiencies in the future.

The system is as effective as a leaf, but unfortunately that means an efficiency around 0.12% in the conversion of sun light into fuel. This is way too little to have a commercial production of chemical energy from the Sun light. Existing photovoltaic panels have an efficiency 100 times better. It is not just efficiency, although this is a very important parameter: a plant can make it do with the very low efficiency by having many leaves (an oak plant can have as many as 200,000 leaves, that is a overall surface of about 200 square meters and that is enough to produce the chemical energy the plant needs, but it would not be enough to light a 100W light bulb!).

It is also about cost. Progress in photovoltaic panels over the last fifty years have dramatically reduced the cost per W, from 200$ to 3.4$ (including all cost, not just the photovoltaic panel…), compare this to the 2.1$ cost per W of a Coal powered system. Clearly a coal system generates a lot of CO2, whilst a photovoltaic panel doesn’t generate any! So one should also take that into consideration….

Power production, distribution and usage is a very complex system and we haven’t discovered so far a silver bullet. Nevertheless, it is good to see continuous progress by scientists to help quench the thirst of energy.

Researchers are pushing the limits of miniaturisation  in electronics, to sustain the evolution towards greater performance (low energy requirements, higher capacity, higher throughputs) and higher density. Silicon is approaching the end of the line and so is the lithographic process (the first limit is more related to physical issues arising once the dimension gets below the 10nm scale, the second is more an economic sustainability issue) and there is a need to find new approaches to manufacture transistors.

Scientists are at work to find suitable materials like germanium and graphene, and even DNA, to go beyond silicon and indeed (as reported in this blog) several solutions have been found. But science is not enough. It just provides the proof that something is possible from a physical point of view. It does not show that it is doable. For that we need technology. Labs prototypes are the technological underpinning to show that indeed some scientific principle can be implemented by some technology.

This is not enough though! We need to have a technology that can be used in an industrial plant for mass production at low cost (economic sustainability).

Diagram of a 3D nano-transistor showing the gate (red) surrounding the vertical nanowires (green) and separating the contacts at the ends of each nanowire (beige) (credit: X-L Han and G. Larrieu/CNRS)

This is what Guilhem Larrieu of the Laboratory for Analysis and Architecture of Systems, in Toulouse, is trying to do, along with his fellow researchers and he is explaining his approach in an article on Nanoscale.

It is now several years that nano wires have been found to have a Schottky junction, that is what is needed to create a transistors, and in the last few years the technology for producing nano wires has been refined. The next step, needed, is to find a way to assemble in an industrial way all the nano wires into a chip. And this is what is reported by the Larrieu team in their article on Nanoscale.

As shown in the picture, the nano wires are densely packed in a vertical structure with the three electrodes inserted at the top, bottom and middle creating transistors. The top and bottom contact plates are made of platinum and serve as the source and drain respectively for the transistor.

Quoting their words on the paper:

“We report a high performance field-effect transistor implemented on massively parallel dense vertical nanowire arrays with silicided source/drain contacts and scaled metallic gate length fabricated using a simple process. The proposed architecture offers several advantages including better immunity to short channel effects, reduction of device-to-device variability, and nanometer gate length patterning without the need for high-resolution lithography. These benefits are important in the large-scale manufacture of low-power transistors and memory devices. ”

It should be noted, however, that what they report is a way to industrially produce nano wire based transistor in an industrial way but the real industrialisation is still in the future.
The point in my post, beyond informing on the progress being made in prolonging the life of the Moore’s law, is to show how complex is the path leading from a scientific discovery to a marketable product and how much ingenuity is required at all steps of the way, and also how much research is needed, not just to come up to an invention but also in every step leading to the commercialisation and usage. More and more we see that research is no longer something that exists in the early stages of the waterfall model. It is actually flanking every step.

And this is why at the EIT ICT LABS we are still talking (and doing) research even if our positioning is at the last part of the sequence leading to the deployment of innovation in the marketplace.

Current storage technologies are based on materials that can change its characteristics (like magnetisation) from one state to another. By attributing a value (0 or 1) to a specific state we can use it to “store” that bit. Changing the state means changing the value of the retained value. And, of course, by reading the state we “read” the value.

There are many technologies that allows us to do just that and the writing and reading occurs via the displacement of electrons. To have a reliable writing and reading, intuitively, you need to have many electrons moving around since they are fleeting and you cannot trust just one of them, nor hundreds…. It follows that you need to have many atoms in the substrate for storing just one bit (many today means in the order of 2 thousands atoms).

Configuration of a resistive storage cell (ReRAM): An electric voltage is built up between the two electrodes so that the storage cells can be regarded as tiny batteries. Filaments formed by deposits during operation may modify the battery’s properties. (Credit: Jülich Aachen Research Alliance (JARA))

Now scientists are learning to build up materials from the bottom up and in this way they can create substances having some desired properties. By applying nano tech a team of scientists of  Jülich Aachen Research Alliance (JARA) have been able to create a storage cell working on ions, rather than on electrons (by the way, living things also use ions, not electrons for their electrical communications). Ions are bigger than electrons, thousands time bigger (a single proton mass is almost 2000 times “bigger” than an electron – if you are picky the real ratio is 1836.152 672 45), and therefore can be controlled much better.

Don’t be misled: using ions doesn’t mean that you have to have bigger cells. When using electrons, implicitly you have to use also the atoms that have those electrons, so you are using electrons and ions…. If you use ions for storing and retrieving information you can have a reliable system with just a few of them. Hence the potential squeeze of dimension and the increase in storage density. In the figure you can se the schematics of the storage cell developed by the team. The size of the cell is 10nm so you can fit 10 billion of them in a single 1 square mm. A cubic mm of these cells would be able to store 1 EB of data (a million TB)!

Of course you cannot pack these cells side by side, and you need connectors so that eventually one could imagine having ONLY one PB (a thousands of TB) in a cubic millimetre. Not bad, though!

Now, we are nowhere near an industrial manufacturing of this kind of storage and what they have is just a paper on the Journal Nature Communications reporting the result of a prototype they manage to build of a single cell.

Even though we are far away from a commercial application, remember that 70 years ago the first transistor was a bulky piece of germanium …

The European Commission has awarded a professor of the Trinity College in Dublin, John Boland, 2.5 million € to continue his studies on nanowire networks with the aim of creating meaningful connections out of a myriad of nanowires.

Nanowires

Nanowires are tiny tubes made of carbon, each one a few atoms wide and several hundreds of thousands of atoms in length. It is not possible, at least with present technology, to create an ordered, structured set of these nano wires. When produced they look like tangled spaghetti, see the photo.

In a way they are similar to the connections made in our brains by the trillions of dendrites connecting neurones. And, like in the brain, the aim is to find ways to reinforce the connections in the random set of existing ones that would make sense to perform a specific function.

In our brain the stimuli we receive from the outside world through our senses lead to a continuous reinforcement of some connections and the weakening of others. The result is what we call learning. More than that. The connections that are most strongly related one another (so that when one is activated the others get activated as well) can be seen as a state, an information state and they lead to an emergent behaviour, something we call “intelligence”, or simply thoughts.

This is what prof. Boland is looking to achieve in his spaghetti like nanowires. He is also working on nanowires that have memristors properties, that is to say that can remember their previous “experience”. This makes them even more like neurones connections in the brain.

It is interesting to note that this approach of creating meaningful network out of a “spaghetti” mess can work thanks to the huge number of nanowires, The probability of existence of potential meaningful connection increases with the increase of numbers of nanowires and above a certain thresholds it is almost guaranteed that such a connection can be found. This relates to the Small World theory and in turns it is at the core of the concept of ecosystems.

Electronics is slowly but steadily make ways in our bodies. Microchips to release drugs, sensors to detect a variety of conditions are already part of the landscape.

The crucial problem to solve remains the powering of these devices. As electronics evolution (Koomey’s law) keeps decreasing the demand for power new approaches are becoming feasible, such as the one proposed by Jia Hao Cheong, a professor at the A*START Institute of Microelectronics in Singapore.

He is addressing the problem of monitoring grafts in the body that surgeons are implanting to create an artificial blood vessel (or substitute a faulty one). The problem with these grafts is that they may become clogged and it is important to monitor what is going on. The solution proposed is to insert in the graft material nanowires that change their resistance as they are stretched, somthing that happens when the blood pressure increases. A sensor can measure this pressure increase by detecting the change in resistance of the nanowires but of course the sensor needs to be powered.

Cheong has found the solution by sending the power wirelessly from the reading device that the doctor holds in her hand, like it is done when reading RFID tags.

As shown in the figure the graft (in this case used in people with kidney failure that need to have dialyses every few days and have a graft implanted to avoid pricking the veins with possible damage and infection) is being monitored by a tablet like device that is sending wireless power sufficient to activate the sensor for both reading the strain in the graft and sending the information, wirelessly, to the tablet.

The power transmitted by the tablet is absorbed also by the body tissue but it is sufficient to power a 12.5 microW sensor up to a depth of 50mm, which is plenty for a graft inserted in arm.

A nano

When you play a guitar each of the six strings “stores” one note. Well, researchers at the Technical University of Munich are looking at using the vibration of a string to store information, more specifically they are trying to use a string made by a single  carbon nanotube to store “quantum” values from 0 to 1.

A carbon nanotube is held at the two extremities and an electromagnetic field makes it vibrate. The nanotube is so small that the vibrations are of the order of millions per second (the shorter the string the higher the frequency…). It can vibrate in many directions and these directions can be measured by a laser beam. It can actually be constrained to vibrate in two specific directions and hence one could associate the value of one to a direction and the value of zero to the other. Or one can relax the constraints and let it vibrates in the 3D space hence potentially assuming any value between 0 and 1.

This mechanism, therefore, can become a component of a quantum computer, able to store an information for as long as a second. It does not seem a very long span of time, but we are talking about quantum phenomena that happens at the nanosecond scale. So as a transient memory used to perform computation one second is long enough.

A microwave cavity resonator

Almost simultaneously, researchers from Yale have published a paper on Nature describing a different approach to store information in a quantum computer. They are proposing to use photons (that interact weakly and seldom with anything else) to store information in a quantum computer.

They have managed to change the state of a photon using a microwave cavity resonator as a medium. Since photons do not interact (basically) with anything else their status, and hence the information associated, can be preserved for a long time.

Another piece is the quantum computing puzzle that anyhow remains at the end of the rainbow. As we make one step forward the end of the rainbow with its pot of gold backtrack one step….

It is not possible yet to fix a date for the first usable running quantum computer.

Solar panels are “old stuff”. They have been around for quite a while and scientists have tried to increase their efficiency in converting light energy into electrical energy. Progress have been made but we are still “wasting” a lot of light energy.

The trade-off is between cost and efficiency. Engineers have been able to create much more efficient solar panels but their cost makes them unpractical. Once in a while we get the news of another ingenious way to increase efficiency, like this one developed by the EPFL (Losanne) and the Niels Bohr Institute in Denmark.

They have discovered that nanowires are very good in focussing light, reaching an intensity 15 times greater than the one in normal solar panels.

Nanowires are smaller than the wavelength of light and this creates a resonance that in turns results in greater focussing capability. You need 10,000 nanowires to get the size of a hair.

The problem, as in several other discoveries, is to translate this into an economical industrial process and the jury is still out to see when this will be possible.

On the other hand, this adds to the list of wonders that can be achieved working at the nano level…

As chips manufacturing gets smaller and smaller we are approaching a cost barrier, well before hitting a physics barrier.

We are now down to the 14 nm and the cost for the nanolithography and for the production plant is skyrocketing.

On the other hand squeezing more and more transistor per square mm is the way to go to increase performances, decrease power consumption and cost. What is needed is a paradigm change in the production approach.

Enter nano tech!

Rather than using etching to create transistors on a silicon wafer researchers are trying new approaches where molecules can self assemble into transistors and chip. To do that they try to mimic Nature where life molecules are created by self assembling more elemental component.

Now Chuanbing Tang, Christopher Hardy and Lixia Ren, researchers at the University of South Carolina, have published a paper to illustrate a process for doing just that.

It is unlikely that this approach, as well others that are currently being tested, will result in the chip in a cell phone within this decade. Actually, we can expect that for many decades to come the etching technology will continue to be mainstream but more and more we can expect to see these nano based technology to flank etching.

The Moore’s law will remain valid for quite some time, even though its progress will follow a direction that Moore is unlikely to have imagined 50 years ago!