THz field‑driven FN tunneling in TiO₂ nanogaps. Credit: ACS Nano (2025). DOI: 10.1021/acsnano.5c12360

A research team affiliated with UNIST has unveiled a quantum device capable of ultra‑fast operation, a key step toward realizing technologies like 6G communications. This innovation overcomes a major hurdle that has long limited the durability of such devices under high electrical fields.

Professor Hyeong‑Ryeol Park from the Department of Physics at UNIST, in collaboration with Professor Sang Woon Lee at Ajou University, has developed a terahertz quantum device that can operate reliably without suffering damage from intense electric fields—something that has been a challenge for existing technologies.

How terahertz quantum devices work

Terahertz quantum devices are considered essential for future high‑speed communication systems, enabling rapid signal processing well beyond the limits of traditional semiconductors. They work by harnessing the quantum tunneling of electrons driven by terahertz waves—high‑frequency electromagnetic waves oscillating trillions of times per second—a phenomenon where electrons pass through energy barriers in a way classical physics can’t explain.

The main obstacle has been that inducing tunneling requires extremely strong electric fields—around 3 V nm⁻¹—which generate a lot of heat. This heat often damages or melts the device’s metal electrodes, making reliable operation difficult.

Innovative materials and fabrication techniques

To tackle this, the team developed a new device that can operate at much lower electric fields—roughly a quarter of what was previously needed. The secret lies in replacing the insulator material sandwiched between the metal electrodes.

• Instead of using the conventional aluminum oxide (Al₂O₃), they used titanium dioxide (TiO₂), which has a lower energy barrier and allows electrons to tunnel with less effort.

The work is published in ACS Nano.

Gangseon Ji, the first author of the study, explained, “Rather than pushing electrons with stronger electric fields, we’re creating pathways that make it easier for electrons to move. Since tunneling is a probabilistic quantum effect, lowering the energy barrier significantly increases the chances of tunneling happening.”

Using advanced atomic‑layer‑deposition techniques, the team produced high‑quality devices. This method, commonly used in semiconductor manufacturing, allowed precise control over the TiO₂ layer, preventing microscopic defects—such as oxygen vacancies—that often occur during thin‑film fabrication.

Professor Sang Woon Lee added, “By applying cutting‑edge deposition technology, we managed to eliminate defects that could weaken the device, ensuring high stability and performance.”

Performance and future applications

The new device demonstrated consistent tunneling operation at electric fields of about 0.75 V nm⁻¹. Thanks to TiO₂’s excellent thermal properties, it maintained stable performance over 1,000 cycles, even when modulating terahertz wave transmission by up to 60 %. This level of stability was a significant achievement, pointing toward practical applications.

Professor Hyeong‑Ryeol Park concluded, “We have addressed the two biggest challenges—high‑voltage operation and heat‑related damage—that have held back the commercialization of terahertz quantum devices. This breakthrough opens the door to ultra‑fast, energy‑efficient optical communication systems beyond 6G and advanced quantum‑sensing technologies.”

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Publication details

Gangseon Ji et al., “Low‑Field Terahertz Quantum Tunneling in Metal–TiO₂–Metal Nanogaps via Schottky Barrier Engineering,” ACS Nano (2025). DOI: 10.1021/acsnano.5c12360.