In an article recently published in the journal Communication Materials, researchers discussed the ability of a graphene/gold bilayer construction to enable the electrically tuneable terahertz metasurface.
Study: Electrically tuneable terahertz metasurface enabled by a graphene/gold bilayer structure. Image Credit: Mathier/Shutterstock.com
The terahertz (THz) bands are perfect for next-generation wireless networks. However, the unavailability of components and technology that can operate at frequencies beyond those of present electronic and photonic frequencies has hindered the development of THz wireless communication systems.
Two-Dimensional (2D) Materials
To create electrical and photonic devices operating at terahertz frequencies, novel materials, such as 2D materials like graphene, and device designs including ultrafast charge carrier dynamics and necessary capabilities are highly desired. Electrically tuneable, frequency-selective terahertz absorbers with high Q-factor resonances are highly desired yet difficult to find for constructing terahertz systems. The growing interest in metamaterials and 2D materials to provide reconfigurable, tuneable, and programmable features for terahertz applications results from the absence of tuneable devices in the terahertz area.
For terahertz devices, graphene-based metamaterials have drawn a lot of interest. One of the most difficult aspects of developing graphene-based electronics is fabricating graphene into scalable, usable, and functioning electronic devices. To develop state-of-the-art graphene-based tunable metamaterial devices, new metamaterial architectures and production techniques are required.
Electrical Modulation of Terahertz Waves using Graphene
In this article, the authors added graphene to a superimposed graphene/gold bilayer metamaterial structure, allowing for effective electrical modulation of terahertz waves. This graphene/gold bilayer metamaterial strategy was used to design and experimentally create a 0.2 terahertz frequency-selective absorber. The proposed device maintained a benchmark high-quality factor resonance performance while demonstrating 16 decibels amplitude tuning at 0.2 terahertz resonance and over 95% broadband modulation at just 6 volts bias voltage.
The team addressed the poor performance of graphene metasurfaces and the lack of tunability of gold metasurfaces by preparing a gold and graphene bilayer metamaterial structure. To prove the effectiveness of the proposed bilayer strategy, a highly tuneable terahertz frequency-selective absorber was created and tested.
The researchers illustrated the development of a graphene metamaterial-based device operating in the 0.1–1 terahertz communications window, where graphene was patterned onto the entire complex structure of the metasurface, producing a high-quality benchmark resonance with Q-factor up to 19 having significant amplitude tuning of 16 decibels at a low bias of 6 volts.
The tuning mechanism was detailed together with the design theory, modeling, and experimental data. A flexible and high-frequency laminate circuit board served as the foundation for the device.
Tunable Performance and Broadband Response of the Metamaterial Structure
The fitted resonance shifted from 0.192 to 0.187 terahertz and its amplitude increased from about 18 to 25 decibels. With a graphene conductance range of 40 to 100 millisiemens, the simulated peak amplitude shifted from -17 to -22 decibels. These values were very similar to those that were measured experimentally and were -18 decibels at unbiased and -25 decibels at 6 volts bias resonant amplitudes.
The imaginary portion of the graphene conductivity marginally increased with applied voltage. Although the design and modeling of the metadevice were concentrated on the 0.2 terahertz range, higher-order resonances and broadband features were noted. There were auxiliary modes at 0.36 terahertz, 0.40 terahertz, and 0.56 terahertz. Modulation depth (MD) was 85% between 0.23-0.32 terahertz, 91% between 0.43-0.50 terahertz, and 95% above 0.72 terahertz.
Conclusions and Future Perspectives
In conclusion, this study discussed the development of a bilayer metamaterial structure in which the entire device design was superimposed onto graphene and gold. The experimentally developed graphene/gold bilayer terahertz frequency-selective absorber exhibited tuning performance of over 16 decibels at just 6 volts bias voltage while maintaining a benchmark high Q-factor of 19. With the same low 6 volt bias, the device also had broadband tuning that was greater than 95%.
The theoretical prediction of the tunability for the bilayer metamaterial design was validated by the experimental findings, which were in good agreement with those of theoretical modeling.
The authors stated that a large variety of terahertz devices could easily be fabricated using the proposed scalable fabrication process. They believe that the novel material and device technologies being advanced in this work will impact developing industries like terahertz satellite target tracking, wireless communications, and sensing.
Squires, A. D., et al. (2022) Electrically tuneable terahertz metasurface enabled by a graphene/gold bilayer structure. Communications Materials 3(56). https://www.nature.com/articles/s43246-022-00279-7