Electronics - Page 40

Researchers from the Naval Research Laboratory (NRL) shown that the valley degree of freedom in graphene can be polarized through scattering off a line defect. This makes valley-based electronics (valleytronics) one step closer to reality. Valleytronics may present a middle-ground between spintronics and electronics using the valley degree of freedom (which exists in certain crystals, including graphene).

The NRL research shows that an extended line defect in graphene acts as a natural valley filter. "As the structure is already available, we are hopeful that valley-polarized currents could be generated in the near future" said Dr. Daniel Gunlycke who made the discovery together with Dr. Carter White. Both work in NRL's Chemistry Division.

Researchers from the National Institute of Standards and Technology (NIST) have shown that the electronic properties of two layers of graphene vary on the nanometer scale - not only in the strength of the electric charges between the two layers but they also actually reverse in sign to create randomly distributed puddles of alternating positive and negative charges.

This means that bi-layer graphene (two stacked graphene sheets) acts more like a semiconductor that a single sheet. A band gap may also form on its own due to variations in the sheets' electrical potential caused by interactions among the graphene electrons or with the substrate.

Researchers from IBM developed a graphene transistor with a record cut-off frequency of 155 Ghz and the shortest gate length ever (just 40nm). They used a diamond-like carbon as the top layer of the substrate on which the Graphene is deposited. This material is a great substrate for Graphene. It's a non-polar dielectric material - so it does not 'trap' or scatter charges, doesn't absorb a lot of water and has excellent thermal conductivity. It's also cheap to make and widely used today in the semiconductor industry.

Just over a year ago, IBM developed a 100Ghz RF graphene transistor - so the recent development is a 50% improvement over the previous design.

Georgia Tech Professor Walt de Heer predicts that Graphene will not follow the model of using standard field-effect transistors, but will pursue devices that use ballistic conductors and quantum interference. The Professor's research team hopes to show a basic quantum interference switch within a year.

Taking advantage of the wave properties will allow electrons to be manipulated with techniques similar to optical control, for instance switching may be carried out using interference - separating beams of electrons and then recombining them in or out of phase to switch the signal.

Researchers from the University of Arizona, MIT and Japan's NMSI discovered that placing graphene on boron nitride (instead of the commonly used silicon dioxide) could significantly improve its electronic properties.

Boron nitride is structurally basically the same as Graphene, but it's different electronically - Graphene is a conductor and boron nitride is an insulator. Putting graphene on an insulator makes it possible to study the properties of Graphene alone.

Researchers from the A*STAR Institute of Materials Research and Engineering and the National University of Singapore have developed an improved design for a Graphene based field-effect transistor (FET). The new device includes an additional silicon dioxide (SiO2) dielectric gate below the graphene layer. This allows for simplified bit writing by providing an additional background source of charge carriers.

The new device can lead the way towards ;grapheneferroelectric FETs to be used for nonvolatile memory. The researchers say that the new design achieved impressive practical results - symmetrical bit writing with a resistance ratio between the two resistance states of over 500% and reproducible nonvolatile switching over 100,000 cycles.

Researchers from the National Physical Laboratory (NPL) together with an international team of scientists have published a research into how light can be used to control the electrical properties of graphene. This research opens the door to highly sensitive graphene based electronic devices.

The researchers have revealed that when graphene is coated with light sensitive polymers, its unique electrical properties can be precisely controlled and therefore exploited. The polymers also protect the graphene from contamination. Light modified graphene chips have already been used at NPL in ultra precision experiments to measure the quantum of the electrical resistance.

Researchers from ETRI, South Korea has recently build a flexible Memristor using thin Graphene oxide films. These new Memristors should be cheaper and easier to make as they can be roll-to-roll printed on plastic sheets.

Memristors change their resistance depending on the direction and amount of voltage applied, and they remember this resistance when the voltage is removed. The researchers use a similar design to the one used by HP (which hopes to have Memristor chips ready within 3 years), but they are swapping the titanium dioxide that HP is using with Graphene Oxide. This makes them cheap and flexible, but also much larger (1000 times in fact!). So this is not suited for high-density memory, but rather for applications such as RFID for example. 

Researchers from the University of Illinois used a dry deposition method they developed to deposit pieces of graphene on semiconducting substrates and on the electronic character of graphene at room temperature they observed using the method. The reported their finding in a paper titled "Separation-Dependent Electronic Transparency of Monolayer Graphene Membranes on III-V Semiconductor Substrates".

The paper gives insight into a "understanding substrate-graphene interactions toward integration into future nanoelectronic devices". The project investigated the electronic character of the underlying substrate of graphene at room temperature and reports on "an apparent electronic semitransparency at high bias of the nanometer-sized monolayer graphene pieces observed using an ultrahigh vacuum scanning tunneling microscope (UHV-STM) and corroborated via first-principles studies." This semitransparency was made manifest through observation of the substrate atomic structure through the graphene.

Osaka's university has a Spintronics research group that is working towards MRAM and STT-RAM using several materials including Graphene. Here's a nice intro video about the group: