NEWBORN: Advanced Technology for Sub-THz Waveguides Based on Carbon Nanotubes
The main objective is to demonstrate the experimental proof-of-concept of an alternative/disruptive Carbon Nanotube (CNT) based air filled waveguide technology in the sub-THz range around 300GHz.
In this context, this project will focus on the development of passives, for 3D heterogeneous integration, which requires innovative circuits such as waveguides which will be: easily integrated in a 3D approach, compact, easy to fabricate for low-cost production, low loss for better connectivity, etc.
Telecom communities are beginning to prepare the next generation of telecom, the beyond-5G to 6G, and present KPIs going to a peak data rate of 1Tb/s (50 times the peak data rate of 5G), space multiplexing, spectrum agility, dense massive multiple-input multiple-output (MIMO), wide bands, and so forth.
To achieve Tb/s transmissions in 6G, it is inevitable to utilize the frequency band over 100GHz or sub-THz due to enormous amount of available bandwidth. According to the Infocomm Media Development Authority (IMDA), Singapore frequency allocation chart (Figure 1), the frequency band for IMDA from 30-300GHz is still vacant.
Figure 1. Singapore frequency allocations chart.
Figure 2. Skin depth of different types of CNT material, as well as Cu, as a function of frequency. SW: Single Wall MW: Multi Wall.
Figure 3. Ratio of high-frequency effective resistance with respect to dc resistance for different types of CNT bundles and Cu.
Figure 4. Images of various CNT structures fabricated by CNT transfer technology.
Figure 5. Schematic of CNT transfer process flow
- Use of CNTs for the realization of waveguide up to 300 GHz as opposed to conventional metal-based structures
- Ease in fabricating patterned CNTs based structures, with any type of geometry and high resolution
- Great potential due to:
- 3x stronger electric current carry capacity
- 600x longer mean free path along the axis than traditional metal material (Cu)
- 8x higher thermal conductivity
- Negligible skin effect of CNTs at 300 GHz and above.
- Reduced insertion loss at the THz range
- Skin effect in CNTs bundles is significantly reduced (bigger skin depth) compared to that in metal conductors (Figure 2)
- Lower effective resistance at high frequencies (Figure 3)
- Advantages of CNTs bulk structures fabrication using CNT transfer technology.
- Process is performed at MMIC compatible temperature (< 300°C)
- Easy integration of transferred CNTs as final process step onto device substrate
- Low electrical resistance between CNTs and substrate (0.25-0.5Ω)
- CNTs can be transferred onto various types of substrate
- Improved transfer success rate (up to 90%)
- Single-step transfer of CNT with different heights (µm to mm)
- High CNT height uniformity ±10 µm (~2.5% height deviation)
- The first proof of concept CNTs-based high frequency waveguide technology (Figure 4) enables CNTs structures to serve as building blocks for future high frequency systems
CINTRA (CNRS/NTU/THALES) and CNRS-XLIM have developed since 2009 a large knowledge on the use of CNTs for high-frequency applications and in particular for 3D nano-packaging (flip-chip bonding, EM isolation and wireless interconnects). They demonstrated that the use of CNT is an alternative approach for innovative solutions dedicated to 3D heterogeneous integration. And as shown in Figure 6, the concept of CNT based air-filled waveguide (Figure 4) has been experimentally validated.
Figure 6. Experimental S parameters CNT based air filled waveguide 81-86GHz band.
In this context, this technology will be applied in this project at higher operating frequencies, for the realization of a 300GHz TE10 mode air-filled waveguide, with the following steps :
1. Design, fabrication (Figure 5) and on-wafer characterization in the 300GHz band.
2. Showcase a first working CNT based waveguide prototype fabricated by the patented transfer process with targeted low insertion loss below 1dB/mm and benchmarking its performance with current state of the art in high frequency operations.
3. Assess the performances of the CNT based components to handle 6G modulated signals at 300GHz.
4. Draw conclusion on the feasibility of using CNT for future high frequency applications and suggestions for future work and developmental plans.
This research is supported by the National Research Foundation, Prime Minister’s Office, Singapore under its Campus for Research Excellence and Technological Enterprise (CREATE) programme.
CREATE is an international collaboratory housing research centres set up by top universities. At CREATE, researchers from diverse disciplines and backgrounds work closely together to perform cutting-edge research in strategic areas of interest, for translation into practical applications leading to positive economic and societal outcomes for Singapore. The interdisciplinary research centres at CREATE focus on four areas of interdisciplinary thematic areas of research, namely human systems, energy systems, environmental systems and urban systems. More information on the CREATE programme can be obtained from www.create.edu.sg.
Visit the CNRS website here.