Germanium Nanoelectronics

In the world of miniaturization we are always thinking of faster and smaller things. The use of germanium instead of silicon as primary material of transistor would provide us smaller transistor chip which are faster than its previous counterparts.

During the production of transistor, foreign atoms such as phosphorus and boron are implanted into the semiconductor material so that it becomes partly conducting. But this production step damages the material; it must be repaired by subsequent annealing. As the phosphorus atoms are strongly redistributed within the material during annealing, it has not been possible to manufacture large scale integrated transistors using germanium.

Scientists of the research center Forschungszentrum Dresden-Rossendorf (FZD) surmount this problem with two novel techniques.

Germanium was the basic material of first-generation transistors before it was replaced by silicon at the end of the 1960s. This was due to the excellent electronic properties of the interface between the semiconductor silicon and its insulating and passivating oxide. However, this advantage cannot be utilized if transistor dimensions are further reduced since the oxide must then be replaced by so-called high-k dielectrics. This again stimulates science and industry to search for the most suitable basic material. Higher switching speeds could also be achieved using germanium and some other semiconductors.

By inserting foreign atoms the conductivity of semiconductors can be varied in a purposeful way. One possibility is ion implantation (ions are charged atoms) with subsequent heat treatment, which is called annealing. Annealing of the germanium crystal is necessary as the material is heavily damaged during implantation, and leads to the requested electronic properties. While these methods allow for the manufacturing of p-channel transistors (PMOS) according to future technology needs, it was not possible to produce corresponding n-channel transistors (NMOS) using germanium. This is due to the strong spatial redistribution (diffusion) of the phosphorus atoms which have to be used in manufacturing the n+ regions.

Physicists from the FZD applied a special annealing method that enables repairing the germanium crystal and yields good electrical properties without the diffusion of phosphorus atoms. The germanium samples were heated by short light pulses of only a few milliseconds. This period is sufficient in order to restore the crystal quality and to achieve electrical activation of phosphorus, but it is too short for the spatial redistribution of the phosphorus atoms. The light pulses were generated by the flash lamp equipment which was developed at the research center FZD. Analysis of the electrical and structural properties of the thin phosphorus-doped layers in germanium was performed in close collaboration with colleagues from the Belgian microelectronics center IMEC in Leuven and from the Fraunhofer-Center for Nanoelectronic Technologies (CNT) in Dresden.

STRANGE CARBON NANOTUBES!

Carbon nanotubes (CNTs) are 'strange' nanostructures in a sense that they have both high mechanical strength and extreme flexibility. Deforming a carbon nanotube into any shape would not easily break the structure, and it recovers to original morphology in perfect manner. Researchers in China are exploiting this phenomenon by making CNT sponges consisting of a large amount of interconnected nanotubes, thus showing a combination of useful properties such as high porosity, super elasticity, robustness, and little weight (1% of water density).

The nanotube sponges not only show exciting properties as a porous material but they also are very promising to be used practically in a short time. The production method is simple and scalable, the cost is low, and the sponges can find immediate use in many fields related to water purification.

One of the researchers explains that the nanotube sponges are a completely new structure compared with artificial porous materials in several aspects. The sponge is built entirely with nanotubes through a random (yet desired) interconnection. With a high porosity of >99%, the sponge can be compressed to less than 10% of its original volume yet still recover perfectly. Usually, porous materials tend to become brittle at increasing porosity, thus obtaining a material with both high porosity and flexibility has been challenging.

Carbon nanotubes could take advantage of their high surface area and excellent mechanical strength and flexibility. The scientists synthesized the sponges by a chemical vapor deposition (CVD) process during which the CNTs (multi-walled nanotubes with diameters in the range of 30 to 50nm and lengths of tens to hundreds of micrometers,) self-assembled into a porous, interconnected, three-dimensional framework.

The growth process of the sponges is like a consecutive stacking and penetration of numerous CNT 'piles' into centimeter thickness, which is substantially different from aligned arrays where most of CNTs grow continuously from the bottom to top surface or thin sheets where CNTs were densified into a two-dimensional network during vacuum filtration.

According to the scientists, the CNT sponges are capable of absorbing a wide range of solvents and oils with excellent selectivity, recycle ability, and absorption capacities up to 180 times their own weight, two orders of magnitude higher than activated carbon.

The potential application areas for these sponges are vast. They could be used in large-area oil spill clean-ups, water purification and toxic gas filtration. In addition to environmental applications, the CNT sponges can find use as protective coating, thermal insulator, and high strength-to-weight composite. For example, the sponges can absorb mechanical energy during large-strain deformation, therefore resist foreign force or impact. Their high surface area and porosity are also useful for supporting fine catalyst particles in photo-catalytic devices and fuel cells.

NANOCOMPOSITES COULD CHANGE DIABETES TREATMENT

The people who are suffering from diabetes may soon be able to wear contact lenses that continuously alert them to variations in their glucose levels by changing colors. This facility reduces the need to routinely draw blood throughout the day.

The non-invasive technology, developed by Chemical and Biochemical Engineering professor Jin Zhang at The University of Western Ontario, uses extremely small nanoparticles embedded into the hydrogel lenses. These engineered nanoparticles react with glucose molecules found in tears, causing a chemical reaction that changes their color.

Zhang received $216,342 from the Canada Foundation for Innovation (CFI)  to further develop technologies using multifunctional nanocomposites.These technologies have vast potential applications beyond biomedical devices, including for food packaging. For example, nanocomposite films can prevent food spoilage by preventing oxygen, carbon dioxide and moisture from reaching fresh meats and other foods, or by measuring pathogenic contamination; others can make packaging increasingly biodegradable.

SURFACE TO TOUCH SCREEN: BY THIN FILMS.

DISPLAX, a Portugal-based company, promises to turn any surface — flat or curved — into a touch-sensitive display. The company has created a thinner-than-paper polymer film that can be stuck on glass, plastic or wood to turn it into an interactive input device.

It is extremely powerful, precise and versatile and film can be used on top of anything including OLED and LCD displays.

Human-computer interaction that goes beyond keyboards and mouse has become a hot new area of emerging technology. Since Apple popularized the swipe and pinch gestures with the iPhone, touch has become a new frontier in the way we interact with our devices.

In the past, students have shown a touchscreen where pop-up buttons and keypads can dynamically appear and disappear. That facilitates the user to experience the physical feel of buttons on a touchscreen. In 2008, Microsoft offered Surface, a multitouch product that allows users to manipulate information using gesture recognition.

Displax’s films range from 3 inches to 120 inches diagonally.

Grids of nanowires are embedded in the thin polymer film that is just about 100 microns thick. A microcontroller processes the multiple input signals it receives from the grid. A finger or two placed on the screen causes an electrical disturbance. The microcontroller analyzes this to decode the location of each input on that grid. The film comes with its own firmware, driver — which connect via a USB connection — and a control panel for user calibration and settings.

Currently, it can detect up to 16 fingers on a 50-inch screen. And the projective capacitance technology that Displax uses is similar to that seen on the iPhone, so the responsiveness of the touch surface is great.

And if feeling around the screen isn’t enough, Displax allows users to interact with the screen by blowing on it. Displax says the technology can also be applied to standard LCD screens.

Displax’s versatility could make it valuable for a new generation of displays that are powering devices such as e-readers. For instance, at the Consumer Electronics Show last month, Pixel Qi showed low-power displays that can switch between an active color LCD mode and an e-reader-like, low-power black-and-white mode. Pixel Qi’s displays, along with other emerging display technologies from the likes of Qualcomm’s Mirasol and E Ink’s color screen are keenly awaited in new products because they promise to offer a good e-reader and a netbook in a single device.

But touch is a feature that is missing in these emerging displays. Displax could help solve that problem.

It is also more versatile than Microsoft Surface. The film is about 100 microns thick, while Surface is about 23 inches deep. Surface is not just another hardware solution, it includes integrated software applications and vision technology so it can respond to just the shape of the object.

Displax’s thin film offers a big breakthrough for display manufacturers because it they don’t have to make changes to their manufacturing process to use it. Displax says the first screens featuring its multitouch technology will start shipping in July.

NANOPARTICLE ORGANIC MEMORY FIELD-EFFECT TRANSISTOR

For the first time, CNRS (Centre National de la Recherche Scientifique; National Center for Scientific Research) and CEA researchers have developed a unique transistor that can simulate the main functionalities of a synapse.

This organic transistor, based on pentacene and gold nanoparticles and known as a NOMFET (Nanoparticle Organic Memory Field-Effect Transistor), has revolutionized modern computing world and inspired the researchers to create new generations of neuro-inspired computers, capable of responding in a manner similar to the nervous system.

In the development of new information processing strategies, one approach consists in mimicking the way biological systems such as neuron networks operate to produce electronic circuits with new features. In the nervous system, a synapse is the junction between two neurons, enabling the transmission of electric messages from one neuron to another and the adaptation of the message as a function of the nature of the incoming signal. For example, if the synapse receives very closely packed pulses of incoming signals, it will transmit a more intense action potential. Conversely, if the pulses are spaced farther apart, the action potential will be weaker. It is exactly the nature what researchers succeeded to have copied in the NOMFET.

A transistor, the basic building block of an electronic circuit, can be used as a simple switch - it can then transmit, or not, a signal - or instead offer numerous functionalities for example :amplification, modulation, encoding, etc.

The innovation of the NOMFET resides in the original combination of an organic transistor and gold nanoparticles. These encapsulated nanoparticles, fixed in the channel of the transistor and coated with pentacene, have a memory effect that allows them to transmit in a way a synapse does during the transmission of action potentials between two neurons. This property therefore makes the electronic component capable of evolving as a function of the system in which it is placed. Its performance is comparable to the seven CMOS transistors that have been needed until now to achieve this plasticity.

The devices produced have been optimized to nanometric sizes in order to be able to integrate them on a large scale. Neuro-inspired computers, produced using this technology, are capable of functions comparable to those of the human brain.

Unlike silicon computers, widely used in high performance computing, neuro-inspired computers can resolve much more complex problems, such as visual recognition.