UNIST Professor Kim Myung-soo (from left), and researchers Pyo Chang-woo and Park Seong-mun, who conducted the study. [UNIST]
UNIST Professor Kim Myung-soo (from left), and researchers Pyo Chang-woo and Park Seong-mun, who conducted the study. [UNIST]

Researchers have developed a new semiconductor device for 6G communications based on a two-dimensional semiconductor thin film made by applying ink-state raw materials onto a substrate.

A team led by Kim Myung-soo, a professor in the Department of Electrical and Computer Engineering at the Ulsan National Institute of Science and Technology (UNIST), announced Wednesday that it had developed a low-power, high-performance radio frequency switch capable of operating up to 67 gigahertz (GHz) using a molybdenum disulfide (MoS₂) thin film produced through a solution process.

RF switches are essential semiconductor components that connect or block the flow of high-frequency signals in smartphones, satellite communications, radar systems, wireless base stations and autonomous driving equipment.

Systems that use large numbers of antennas and frequency channels simultaneously — such as 6G and space communications networks — require switches that combine low insertion loss, high isolation and low power consumption.

The switch recorded insertion loss of less than 0.1 decibels (dB) and isolation of more than 35 dB at 67 GHz in a shunt configuration. In practical terms, when a high-frequency signal oscillating 67 billion times per second enters the switch, roughly 98 percent of the input signal passes through with almost no loss, while signal leakage when the switch is off is suppressed to 0.03 percent or below. Although higher frequencies typically produce greater signal loss and leakage, the switch maintained low insertion loss and high isolation even in the millimeter-wave band used for 6G and satellite communications. The product of on-resistance and off-capacitance — a composite figure of merit for switching performance — reached approximately 0.8 femtoseconds, achieving what researchers call "sub-femtosecond" performance below the 1-femtosecond threshold.

The molybdenum disulfide thin film at the heart of the switch is produced through a solution process, making manufacturing straightforward and easy to apply over large areas.

Structure and performance of the solution-processed molybdenum disulfide-based nonvolatile RF switch. [UNIST]
Structure and performance of the solution-processed molybdenum disulfide-based nonvolatile RF switch. [UNIST]

Solution processes typically generate defects in which sulfur atomic sites are left vacant, but in this semiconductor switch those sulfur vacancies serve a useful purpose — providing consistent pathways for copper ion migration and thereby improving durability. A switch built from mechanically exfoliated molybdenum disulfide thin film lasted only about 100 switching cycles, while the solution-processed version maintained its performance through 2,000 cycles.

The study demonstrated that two-dimensional semiconductor thin films produced through solution processing can go beyond being merely low-cost materials and be used in high-performance RF switches and phase-control circuits operating in the millimeter-wave band.

"Because the switch retains its state even when power is cut, it draws no standby power," Kim said. "It could be used to make 6G, satellite communications, radar and defense radio-control systems smaller and more energy-efficient."

The research, supported by the National Research Foundation of Korea and the Institute of Information and Communications Technology Planning and Evaluation under the Ministry of Science and ICT, was published in Nature Communications.


nbgkoo@heraldcorp.com