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Towards Ubiquitous GRAphene based RF COmmunications - demonstrating and understanding graphene based plasmonic THz antenna potential and limitations

Subject Area Electronic Semiconductors, Components and Circuits, Integrated Systems, Sensor Technology, Theoretical Electrical Engineering
Experimental Condensed Matter Physics
Term from 2015 to 2019
Project identifier Deutsche Forschungsgemeinschaft (DFG) - Project number 279150938
 
Final Report Year 2024

Final Report Abstract

The TUGRACO project investigates the feasibility of RF antennas made of graphene. Graphene shows tunable plasmonic effects at frequencies around a few terahertz. Its extraordinary dispersion relation leads to miniaturized and tunable devices at those frequencies. This is necessary for future applications, i.e. Wireless Network on Chip or nanosensor networks, which could enable several new applications e.g. in healthcare. Furthermore, future communication bands in the 5G standard for (ultra) short-range communication are expected to be located in the Terahertz regime. By the use of graphene based antennas, the corresponding antennas can be integrated in devices with restrictions in physical dimension, where metallic antennas are comparatively too large. Through simulations and the corresponding experimental prototype measurements, the project is currently advancing towards a fundamental understanding of the potential and limitations of the graphene antennas under realistic and technologically achievable parameters. This is an important step towards the implementation of wireless communications at the microscale, enabler of disruptive applications such as wireless on-chip communications or nanosensor networks. The investigated samples are based on a standard photoconductive antenna based on a Grischkowsky design. The antenna consists of two graphene patches, which are contacted to a DC bias voltage by gold conducting lines. As a substrate a direct semiconductor (Gallium arsenide) is used. A fs laser pulse is focussed on the antenna gap and excites charge carriers in the substrate. The photo-electrically excited charge carriers are accelerated by an external bias voltage and create plasmons in the antenna arms.We successfully produced and transferred graphene on a substrate and shaped antennas by electron-beam lithography. After the measurements on a T-type antenna (mid term report), which showed a poor influence of the graphene structure, we measured antennas in the H-type configuration. As a first test, we performed measurements on gold reference structures and measured a THz signal at 500 GHz at an antenna length of 47 µm. Furthermore, graphene antennas showed a THz signal as well. The signal shape was comparable to the one of a gold antenna, but the amplitude was two orders of magnitude lower with the bias voltage doubled. This result was assigned to the electric field enhancement in the antenna gap, which overshadowed the real antenna signal. For further signal enhancement the graphene material quality is crucial. Important factors that decrease the quality are the transfer method and the substrate (superstrate). The formerly used transfer method was based on wet chemistry, which was shown to decrease the graphene mobility significantly. Thus we strive for a pure dry transfer. Gallium arsenide as a semiconductor significantly influences the graphene quality. For this reason, we are looking for alternatives in order to increase the graphene material quality. When overcoming the aforementioned problems we expect the graphene antenna to radiate in a frequency range significantly below that of their metallic counterparts with the same physical dimensions.

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