Enhanced coupling efficiency in geometric terahertz rectennas based on scalable CVD graphene

Ubiquitous electromagnetic radiation from wireless communication networks is an untapped energy source for low-power devices. Passive rectennas (a combination of a rectifier and an antenna) can harvest this energy to power devices and systems, such as autonomous sensors. Rectennas based on conventional rectifiers, however, lack the frequency response and zero-bias performance required to extend passive energy harvesting into the terahertz (THz) domain, which is crucial for Internet of Things (IoT) applications in the 6G era. In contrast, rectennas based on geometric rectifiers are ultrafast detectors that can operate without an external bias, making them ideally suited for zero-bias THz detection and energy harvesting. Geometric rectifiers require largely scatter-free, quasi-ballistic charge transport, which is typically achieved only in high-purity materials, which – as in the case of mechanically exfoliated graphene – may not be suitable for wafer-scale fabrication. In this work, we used commercially available graphene grown by chemical vapor deposition (CVD) to fabricate geometric rectennas and demonstrate operation up to 0.68 THz at zero bias. We employed a parallel arrangement of multiple rectifiers to increase the coupling efficiency between the rectifiers and the antennas, and thus the overall rectenna voltage responsivity up to 11 V/W with a corresponding minimum thermal noise equivalent power of 1.9 nW/√Hz under isotropic normalization. Our results are a critical step towards large-scale fabrication of efficient geometric rectennas and enabling THz energy harvesting for low-power IoT devices.