Oxides for Rectenna Technology

The quest to harvest untapped renewable infrared energy sources has led to significant research effort in design, fabrication and optimization of a self-biased rectenna that can operate without external bias voltage. At the heart of its design is the engineering of a high-frequency rectifier that can convert terahertz and infrared alternating current (AC) signals to usable direct current (DC). The Metal Insulator Metal (MIM) diode has been considered as one of the ideal candidates for the rectenna system. Its unparalleled ability to have a high response time is due to the fast, femtosecond tunneling process that governs current transport. This paper presents an overview of single, double and triple insulator MIM diodes that have been fabricated so far, in particular focusing on reviewing key figures of merit, such as zero-bias responsivity (β₀), zero-bias dynamic resistance (R₀) and asymmetry. The two major oxide contenders for MIⁿM diodes have been NiO and Al₂O₃, in combination with HfO₂, Ta₂O₅, Nb₂O₅, ZnO and TiO₂. The latter oxide has also been used in combination with Co₃O₄ and TiO_x. The most advanced rectennas based on MI²M diodes have shown that optimal (β₀ and R₀) can be achieved by carefully tailoring fabrication processes to control oxide stoichiometry and thicknesses to sub-nanometer accuracy.