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 ( β 0), zero-bias dynamic resistance ( R 0) and asymmetry. The two major oxide contenders for MI nM diodes have been NiO and Al 2O 3, in combination with HfO 2, Ta 2O 5, Nb 2O 5, ZnO and TiO 2. The latter oxide has also been used in combination with Co 3O 4 and TiO x. The most advanced rectennas based on MI 2M diodes have shown that optimal ( β 0 and R 0) can be achieved by carefully tailoring fabrication processes to control oxide stoichiometry and thicknesses to sub-nanometer accuracy.