2022.02.04
Research team led by Professor Seong-Il Im (Department of Physics) at Yonsei University has developed a 27 GHz high frequency schottky commutator for 5th generation communication using the vertical charge transport phenomenon of iselenium tungsten (WSe2), a two-dimensional layered nano-semiconductor material.
The two-dimensional layered nanomaterial-based electronic device that has been studied so far has been in the limelight as a next-generation semiconductor material to replace silicon semiconductors, but the two-dimensional layered horizontal nanomaterial is the unique property of ultra-thin film semiconductors because of the limited channel/contact volume, eventually high contact resistance, serial resistance, parasitic capacitance was forced to result. In addition, due to the deterioration phenomenon that occurs on the semiconductor surface exposed to the air, the performance of the electronic device is reduced, high-quality problems are more pronounced. Recently, various alternatives have been proposed to overcome these problems, but there are still many difficulties in replacing silicon semiconductors.
In this study, a ‘vertical’ Schottky diode device was produced using a two-dimensional layered nanomaterial, iselenium tungsten(WSe2) semiconductor, rather than a horizontal one. Using the advantages of aluminum oxide insulating film process, inter-layer quantum tunneling charge transport phenomenon, and vertical device structure, ultra-high frequency rectification characteristics of high enough speed(27 GHz)to operate reliably in the fifth generation mobile communication frequency band was implemented on the glass substrate.
Tungsten iselenium oxide(WSe2), a two-dimensional layered nanomaterial, forms a strong schottky contact with the ITO electrode used as a transparent electrode, omic contact with the platinum(Pt) electrode as a P-type semiconductor material. In the existing study, only horizontal diodes were mainly studied and the contact resistance was large, but in this study, the vertical type was tried to obtain the minimum contact resistance.
The vertical device structure was used to optimize the channel/contact volume in the vertical direction to minimize contact resistance, serial resistance, and parasitic capacitance. In addition, the vertical direction channel of the diode itself is protected by contact metal, it was possible to dramatically reduce the deterioration caused by the absorption and desorption of oxygen and moisture in the air.
As a result, this Schottky device allowed only small contact resistance(50Ω), small parasitic capacitance(hundreds fF), and showed ultra-fast blocking frequencies of up to 27 GHz. This is the best value shown in two-dimensional layered materials or thin film materials, except for silicon and gallium visor.
In addition, the researchers used an aluminum oxide film to create their own circuit where Schottky diodes and capacitors are connected in parallel to implement commercial AC/DC converters and AM signal detectors in various frequency domains.
Such a device can be easily fabricated on glass and plastic and can be mounted with antennas and circuits on the interior windows of next-generation cars, which can be effectively applied to fifth-generation communication.
Professor Seong-il Im said,”The vertical high-frequency schottky rectifier applied to the two-dimensional layered nano-semiconductor obtained through this study has excellent ultra-high frequency characteristics in the RF millimeter wave area and is easy to make devices on various substrates, so we expect to receive high academic value as well as practical value."
This study was published in Nature Communications on March 27 as a result of a collaboration with Professor Kwan-pyo Kim(Yonsei, second author)in Physics, Professor Min-wook(Yonsei) in Electronics, and Researcher Jae-Ho Im(University of Michigan, USA), with Seung-jin Yang(Yonsei)as the first author. It was carried out with the support of the leading Research Center Support Project(SRC)and the Leap Research follow-up support project of the Ministry of Science, Technology, Information and Communication.
※ Two-dimensional layered nanomaterial: A low-dimensional nanomaterial in which atoms form a crystal structure in a two-dimensional plane with a single atomic layer thickness(about 1 nm = 1 billionth m), and are combined with a weak van der Waals force between the atomic layers to form a layered structure.