Electronics - Page 33

Researchers from japan's Advanced Industrial Science and Technology (AIST) institute developed a new highly reliable interconnect that features low-resistivity, using multi-layer graphene. They say that this interconnect achieved a resistivity similar to copper (this was achieved by intercalating iron-chloride molecules between the graphene layers. This interconnect may be used to interconnect large-scale integrated circuits (LSIs) to reduce energy consumption.

The researchers used CVD using a cobalt epitaxial film as a catalyst to create the multi-layer graphene. They say that their multi-layer graphene has a structure and electrical properties similar to those of graphene obtained from crystalline graphite, but is i more tolerant than copper to high current densities.

Today two different teams of researchers released articles describing new advances in graphene-on-silicon based photodetectors. These devices hold promise because it could lead to more simple device fabrication - and those devices will be very fast compared to current photo detectors and be responsive to a wider range of light frequencies.

But basic graphene photodetectors suffer from low responsivity as graphene will only convert about 2% of the light passing through it to electrical current. This is a high value for an atom-thick material, but it's not enough for a real photodetector.

During a Q&A session, Intel's CEO Brian Krzanich said that the company is working on graphene technologies and that their researchers are seeing some great progress. But graphene is still "a few generations away".

In the best case scenario Intel sees graphene based products emerging in 2019, but that is rather optimistic.

Researchers from Stanford developed a new way to produce graphene ribbons using DNA strands. GNRs have a bandgap and so can be used as building blocks for transistors, and indeed the researchers produced transistors based on GNRs produced using this new process.

The process goes like this: it starts with a silicon substrate, dipped in a DNA solution (derived from bacteria). They then combed the DNA strands into relatively straight lines (using a common technique). They exposed the DNA to a copper salt solution which allowed the copper ions to be absorbed into the DNA.

The Korean Intellectual Property Office posted some interesting figures today. They report that Korean companies are securing essential patents related to the commercialization of graphene - and several companies are making inroads into graphene production and manufacturing transparent graphene-based displays.

Between 2005 and June 2013 a total of 2,921 graphene-related patents have been applied for in Korea, and the rate is accelerating quickly. 93% of those patents have been applied for by Korean individuals and organizations.

Researchers from MIT developed a new way to p-dope graphene (and open up a bandgap) without harming the material's electronic properties a lot. The process basically dopes with chlorine using a plasma-based surface functionalization technique. The researcher say that their chlorine-doped graphene keeps a high charge mobility (around 1500 cm²/V) after the hole doping.

Using this process, you can get the chlorine to cover over 45% of the graphene surface, the highest surface coverage area reported for any graphene doping material. In theory, covering 50% of the graphene with chlroine in both sides can open up a 1.2 eV band gap. This means that the 45% currently achieved is very close to this target. The researchers plan to start using suspended graphene sheets so that they can cover both sides.

The wall street journal posted an interesting article and video on graphene. The article discusses the current state of research and business, possible graphene applications and the rush to patent related technologies.

The article starts with the Cambridge graphene research center and then discusses several companies and their graphene programs, including IBM, Nokia, BlueStone Global Tech, Vorbeck Materials, Lockheed Martin and Aixtron.

Researchers from the University of Texas developed high performance (25-Ghz) printed graphene field-effect-transistors (G-FETs) on flexible plastic substrates. They say these are the world's fastest such transistors to date.

The researchers are very focused on keeping costs down. The fabrication process started with the non-graphene structures (the electrodes and gates), deposited on sheets of plastic. Separately they grew large sheets of graphene on metal. The graphene was then peeled off and transferred to complete the device. This "graphene-last" approach was chosen because the graphene is very sensitive to all the processing needed to make the other components. The final step was to encapsulate the circuit.

Researchers from the University of California, Riverside developed a graphene based transistor based on negative resistance rather than trying to open up a band gap. Negative resistance is the counterintuitive phenomenon in which a current entering a material causes the voltage across it to drop. It was shown before that graphene demonstrates negative resistance in certain circumstances.

The idea is to take a regular graphene field-effect transistor (FET) and find the circumstances in which it demonstrates negative resistance. This dip in voltage is used as a kind of switch - to perform logic. The researchers showed how several graphene FETs combined can be manipulated to produce conventional logic gates. The researchers designed such circuits that can match patterns (but they have yet to actually produce them).

Bilayer graphene is supposed to have a bandgap, but experiments showed that this material cannot be turned into a real insulator. Now researchers from Berkeley Lab's Advanced Light Source (ALS) institute discovered that this is caused by tiny twists in the bilayer material, caused by subtle misalignments of the two layers. This twist can lead to surprisingly strong changes in the bilayer graphene's electronic properties.

The graphene layers twist produces massive and massless Dirac fermions. This structure prevents bilayer graphene from becoming fully insulating even under a very strong electric field. The researchers explain that Massless Dirac fermions are essentially electrons that act as if they were photons. As a result, they are not restricted by the same band gap constraints as conventional electrons. These new massless Dirac fermions move in a completely unexpected way governed by the symmetry twisted layers.