New communications and radar systems (such as 5G, 6G, and beyond) require small and tunable high-frequency devices, since their backbone is the Internet-of-Things (IoT) that is a wireless network interconnecting tiny objects such as sensors, actuators, and detectors. The need for ultrafast, low-energy-consumption information processing of an exponentially increasing data volume will lead to a global mobile traffic reaching 4394 EB by 2030, thus starting the 6G era of an “ubiquitous virtual existence” when all life activities will be interconnected in real time. Key societal drivers for 6G (data rate up to 1 Tb/s) will be :

• Internet-of-Senses (IoS) (i.e., radar sensors),
• Connected intelligent machines,
• Digitalized and programmable physical world that need to be built on newer technologies delivering non-limiting connectivity, trustworthy systems, and cognitive network.

The next-generation communication technologies (5G: 26–95GHz by 2025 and 6G: 95GHz–3THz by 2030) have stringent requirements and unprecedented needs:

• low bias voltage for beam-steering capabilities;
• increased power efficiency and ultrafast switching times;
• miniaturization for wireless nodes;
• reconfigurability (to implement on-chip antenna multiplexing and antenna tuning);
• frequency scalability (for future increase in bandwidth), among others.

In today’s IoT and IoS applications, radar sensors play one of the major roles. Due to the increased need for higher sensitivity and non-destructive inspection systems, the frequency of the radar sensors has reached up to 300GHz on silicon-based technologies as an early access technology/product. On the other side, 60GHz radar sensing is considered one of the main products for smart home (lighting, automated doors, camera and security, human tracking, gesture sensing), non-destructive material classification, monitoring vital signals (i.e., respiration, heartbeat, or blood pressure), and all the IoT application that need micro-motion detection. The market penetration for these sensors is now hampered by (i)the limited antenna performance (mainly for the 300GHz and above) and (ii) the frequency selectivity and tunability (mainly for the 60GHz case).

Si-based CMOS devices operate close to their theoretical limits in terms of power densities, operating frequencies, and temperature. Furthermore, state-of-the-art sub-THz III-V technologies are prohibitive for ultra-large volume manufacturing needs (50 billion mobile devices by 2030).