G-FET - Page 4

A research team from Chalmers University of Technology in Sweden developed a new subharmonic graphene FET mixer at microwave frequencies. This could pave the way for new opportunities in future electronics as it enables compact circuit technology, potential to reach high frequencies and integration with silicon technology.

A mixer combines two (or more) electronic signals into one or two composite output signals. The ability in graphene to switch between hole or electon carrier transport via the field effect requires a unique niche for graphene for rf ic applications. The researchers say this symmetrical electrical characteristic has enabled them to build a G-FET subharmonic resistive mixer using only one transistor.

IBM researchers has fabricated a 2-GHz graphene frequency doubler RF circuit in a CMOS-compatible manufacturing process, on 8" wafers. To fabricate this the researchers inverted the usual manufacturing process and define gate structures first on silicon wafers and then transfer graphene layers fabricated using chemical vapor deposition to the silicon. After defining the areas of graphene IBM was able to attach source and drain contacts to the graphene to complete FET structures.

Inverted-T gate structure

The device itself, the frequency doubler, integrates multiple field effect transistors and radio frequency passives and demonstrated a conversion gain of approximately -25db (at 2 Ghz).

Graphene can adsorb oxygen onto its surface (which changes graphene's electronic transport properties). This can be useful for Spintronics devices, but the adsorption is difficult to control. Researchers from the Tokyo Institute of Technology developed a way to control the adsorption of oxygen by applying an electric field to a Graphene-based field-effect transistor (FET).

The density of carriers (electrons and holes) in the FET can be tuned by applying an electric field to the gate of the device and, when oxygen molecules then adsorb onto the device, the conductivity of the FET changes.

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 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.

IBM Researchers has opened a bandgap for graphene field-effect transistors (FET) that could someday rival complementary metal oxide semiconductor. This is one of the last roadblocks to commercialization of Graphene-based technology, according to IBM.

Graphene has a higher carrier mobility than Silicon, but lacks a band gap, which has kept the on-off ratio of graphene transistors dismally low—usually less than 10 compared to hundreds for silicon. Now IBM says that they have managed to create a tunable electrical bandgap (up to 130meV) for their bi-layer graphene FETs. And larger bandgaps are possible, too.