Progress in THz Rectifier Technology: Research and Perspectives

Abstract

Schottky diode (SD) has seen great improvements in the past few decades and, for many THz applications, it is the most useful device. However, the use and recycling of forms of energy such as solar energy and the infrared thermal radiation that the Earth continuously emits represent one of the most relevant and critical issues for this diode, which is unable to rectify signals above 5 THz. The goal is to develop highly efficient diodes capable of converting radiation from IR spectra to visible ones in direct current (DC). A set of performance criteria is investigated to select some of the most prominent materials required for developing innovative types of electrodes, but also a wide variety of insulator layers is required for the rectification process, which can affect the performance of the device. The current rectifying devices are here reviewed according to the defined performance criteria. The main aim of this review is to provide a wide overview of recent research progress, specific issues, performance, and future directions in THz rectifier technology based on quantum mechanical tunneling and asymmetric structure.

Nanomaterials and Devices for Harvesting Ambient Electromagnetic Waves

“…Their thickness must be in the range 2–6 nm to ensure the occurrence of the tunneling effect, with the actual thickness depending also on the roughness of the metal that is used (a low roughness allows the deposition of thinner insulator layers). IR rectennas based on oxides are being further developed on the basis of more efficient MIM structures, such as MI n M (where “I n ” indicates an n-layer insulator), i.e., relying upon oxide heterostructures to increase the nonlinearity of the diode and its cutoff frequency [ 30 ].…”

A mid-IR Plasmonic Graphene Nanorectenna-based Energy Harvester to Power IoT Sensors

“…The nanoantenna represents only a passive device unable to convert the high frequency signal harvested directly in DC power [29]. Therefore, an ultra-high speed diode able to rectify THz frequencies is mandatory.…”

“…As first step, a nanoantenna value Vopen =1.6 mV was obtained by CST studio simulation, and a value of ZA=3,4 kΩ was obtained corresponding to the resonant frequency f=28,3 THz. Metal insulator metal diodes, which may be used up to 30 THz, must show adequate figure of merits (FOMs) as asymmetry, (Asym) nonlinearity (NL) and responsivity (S) around zero bias and cut-off frequency [29]. The thickness of the oxide layer is 15 nm, whereas the thickness of the metal is around 100 nm.…”

Parallel metal–insulator–metal diode with an ultrathin spin-coated hydrogen silsesquioxane insulating layer

“…22) The thin insulator in MIM, usually in the range of 1 ∼ 5 nm, has a great effect on the figures of merit of MIM diodes. [22][23][24] Poor-quality insulators may cause serious problems such as the direct connection of electrodes if there exist some pinholes in the insulating layer. Thick insulators often exponentially reduce the possibility of tunneling and significantly increase the resistance of a MIM diode.…”