Researchers from the Chalmers University of Technology at Gothenburg in Sweden have for the first time demonstrated a novel subharmonic graphene FET mixer at microwave frequencies. The mixer offers new opportunities in future electronics as it enables compact circuit technology, has the potential to reach high frequencies and integration with silicon technology, according to a Chalmers press note.
A mixer is a key building block in all electronic systems – a device that combines two or more electronic signals into one or two composite output signals. Future applications at THz frequencies such as radar systems for security and safety, radio astronomy, process monitoring and environmental monitoring will require large arrays of mixers for high-resolution imaging and high-speed data acquisition. Such mixer arrays or multi-pixel receivers need new type of devices that are not only sensitive but also power-efficient and compact.
A SEM (Scanning Electron Microscope) image of a subharmonic graphene-FET mixer, which utilises the ability in graphene to switch between hole or electron carrier transport via the field effect.
The ability in graphene to switch between hole or electron carrier transport via the field effect enables a unique niche for graphene for RF IC applications and because of this symmetrical electrical characteristic, researchers at Chalmers have managed to build the G-FET subharmonic resistive mixer using only one transistor. No extra feeding circuits are therefore needed, making the mixer circuit more compact when compared with conventional mixers. As a result, the new type of mixer needs less wafer area when constructed and can open up for advanced sensor arrays, for example for imaging at millimetre waves and even sub millimetre waves as G-FET technology progress.
“The performance of the mixer can be improved by further optimising the circuit, as well as fabricating a G-FET device with a higher on-off current ratio. Using a G‐FET in this new topology enables us to extend its operation to higher frequencies, thereby exploiting the exceptional properties of graphene. This paves the way for future technologies operating at extremely high frequencies,” said Jan Stake, professor of the research team.
Besides enabling compact circuits, the G-FET offers the scope to reach high frequencies due to the high velocity in graphene, and the fact that a subharmonic mixer only requires half the local oscillator (LO) frequency compared to a fundamental mixer. This property is attractive especially at high frequencies (THz) where there is a lack of sources providing sufficient LO-power.
Schematic picture of a subharmonic graphene-FET mixer. The LO and RF signals are fed to the gate and drain terminals, respectively, and the IF signal is extracted from the drain terminal.
The G-FET can be integrated with silicon technology. For example, it is CMOS compatible (Complementary Metal Oxide Semiconductor) and among other things it can be used in CMOS electronics for backend processing on a single chip.
First produced only in 2004, graphene has rapidly gone from curiosity-driven to applied research.
Read more about the active research into graphene at Chalmers at http://www.chalmers.se/en/news/Pages/Millions-in-research-to-take-graphene-out-of-the-lab.aspx
For more information, contact Jan Stake, Department of Microtechnology and Nanoscience, Chalmers University of Technology, at firstname.lastname@example.org