6G wireless networks will use flat panels that actively amplify and steer radio signals to overcome blockages and interference. Today’s mobile networks rely on base stations that broadcast signals broadly, wasting energy and leaving dead zones behind walls or in crowded spaces. Existing reflective surfaces that could redirect signals suffer from high losses and slow switching, especially at the millimetre-wave and terahertz frequencies planned for 6G. This project aims to build a new type of intelligent reflecting surface that combines two materials: transition metal oxides that act as ultrafast switches and phase shifters, and resonant tunnelling diodes that amplify weak signals. The team will first develop the switches and phase shifters separately, then integrate them with the amplifiers into a single “meta-atom” that can control both the phase and amplitude of an incoming signal with negligible loss. If successful, the work could enable 6G base stations to beam signals precisely around obstacles, cutting power consumption and extending coverage indoors and in dense urban environments. The project is primarily applied engineering of fundamental materials physics, but the underlying knowledge of how to engineer transition metal oxides for radio-frequency control could also find use in radar, satellite communications, and future sensing systems.
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Re-configurability of radio frequency (RF) and millimeter-wave (mmWave) systems is expected to become the bedrock of 6G wireless communications. Enabling technologies that can support reconfigurability are still emerging. The project aims to develop active intelligent reflecting surfaces (IRSs) with integrated amplifying capability for 6G wireless communication. IRSs have the capability to redirect incoming signals towards specific, desirable paths, mitigating blockages and interference in complex wireless environments. However, bulk materials enabling such reconfigurability are technologically immature, with traditional materials experiencing high levels of insertion losses and low tuning range, particularly at mmWave frequencies and beyond. In this project, the research team aims to develop an IRS technology with no or very low loss and latency. This will be achieved by combining the attractive features of resonant tunnelling diodes (RTDs), such as their low power operation and ability to operate as reflection signal amplifiers, with transition metal oxides (TMOs), capable of acting as DC-controllable ultra-fast switches and phase shifters to yield a meta-atom. The meta-atom formed in this way will have the capability to both alter the phase and amplitude of the incident signal and compensate for the incident signal loss incurred through traversing the IRS through the amplification by the RTDs. The project has four main objectives. The first objective (O1) is to develop TMO-based switches for the control of amplitude of the signals incident on the IRS. The team will develop TMO-based switches using either VO2 or TiO2 for material design, growth realization, and characterization of binary and mixed/doped metal oxides. They will employ both thermal and plasma-assisted atomic layer deposition to engineer materials with controlled stoichiometry and defect levels. The second objective (O2) is to develop TMO-based phase shifters for the control of the phase of the incident signal on the IRS. The team will investigate the idea for phase shifting of a propagating wave interlaced with sub-skin depth metal TMO/insulator structures. They will examine the fundamental limits of the 'single-bit' insulator/TMO/insulator stack and its performance as a function of the TMO type, their switching mechanism, thickness, characteristics of the dielectrics, biasing lines, and the frequency of operation. The third objective (O3) is to develop RTD reflection amplifiers to compensate for the losses in the circuitry of the IRS and offset the high path loss at terahertz (THz). The team will use RTD's negative differential resistance to amplify the input signal before it is reflected back. Microwave RTD low noise reflection amplifiers have already been demonstrated featuring very low power with 10 dB gain at 5.7 GHz. The feasibility of such amplifiers at K and Ka band frequencies with 100 µW level DC power consumption and a high gain of 32 dB has also been recently demonstrated. The project's ultimate goal (O4) is to combine the results of objectives 1, 2, and 3 to create an IRS capable of controlling the amplitude and phase of incident signals with no or very low loss and low latency. The project's outcomes will be significant in the development of 6G wireless communication technology. The research team will generate new knowledge of the underlying processes and physics for engineering TMOs and their integration with RF and mmWave/THz systems. The project will enable new opportunities for the introduction of IRSs in communication systems for 6G and beyond.
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