Graphene FET enables high-frequency mixer circuits

January 3, 2011 — Chalmers University of Technology researchers created a novel subharmonic graphene field-effect transistor (FET) mixer at microwave frequencies, which could serve as the basis of more compact circuit designer at high frequencies, integrated with silicon.

Figure 1. SEM of a graphene FET created at Chalmers.

A mixer combines two or more electronic signals into one or two composite output signals. At THz frequencies, mixers can be used in radar systems, radio astronomy, process monitoring, and environmental monitoring for high-resolution imaging and high-speed data acquisition. Large-scale mixer arrays or multi-pixel receivers require sensitivity, compact form factors, and power efficiency.

Graphene can switch between hole or electron carrier transport via the field effect, a symmetrical electrical characteristic that can benefit radio frequency (RF) applications. Chalmers researchers built the graphene FET (G-FET) subharmonic resistive mixer using only one transistor, circumventing the need for additional feeding circuits that take up space and power. The new type of mixer requires less wafer area when constructed and can open up for advanced sensor arrays, for example for imaging at millimeter waves and even sub millimeter waves as G-FET technology progress.

Further circuit optimization will improve the mixer’s performance, and by fabricating a G-FET device with a higher on-off current ratio, said Jan Stake, professor of the research team. "Using a G-FET in this new topology enables us to extend its operation to higher frequencies."

In addition to enabling compact circuits, the G-FET provides potential to reach high frequencies thanks 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.

Moreover, the G-FET can be integrated with silicon technology. For example, it is compatible with complementary metal oxide semiconductor (CMOS), and could be used in CMOS electronics for backend processing on a single chip, or other applications.
 

Figure 2. 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. SOURCE: Chalmers.

The work is published in IEEE Electron Device Letters. Access it here: http://publications.lib.chalmers.se/cpl/record/index.xsql?pubid=146694
 
Swedish Foundation of Strategic Research (SSF) supported the work.
 
Chalmers University of Technology conducts research and offers education in technology, science and architecture with a sustainable future as its global vision. Chalmers is well-known for providing an effective environment for innovation and has eight priority areas of international significance – Built Environment, Energy, Information and Communication Technology, Life Science, Materials Science, Nanoscience and Nanotechnology, Production, and Transportation. Read more about the active research into graphene at Chalmers:
http://www.chalmers.se/en/news/Pages/Millions-in-research-to-take-graphene-out-of-the-lab.aspx

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