A transistor channel just one atom thick sounds like the perfect foundation for the next generation of computer chips. But the materials needed to control it have tended to erase its advantages. Now researchers at National Yang Ming Chiao Tung University (NYCU) and TSMC Corporate Research say they have found a way around that wall — by redesigning the invisible boundary between materials.

Writing in Nature Electronics on July 31, the team describes monolayer molybdenum disulfide (MoS2) transistors whose performance improved dramatically after inserting a buffer layer just 0.42 nanometers thick — a few atoms — between the semiconductor channel and its gate dielectric.

Two-dimensional semiconductors like MoS2 (a single layer is about 0.7 nm thick) have long been seen as candidates to extend chip scaling beyond silicon. But depositing an insulator directly on the atomically flat surface disrupts the very electrons the gate must control, forcing a trade-off between thin, strong gate control and efficient electron transport.

The NYCU–TSMC team sidestepped that trade-off by growing an epitaxial aluminum layer on chemical-vapor-deposition (CVD) MoS2, then oxidizing it into an ultrathin aluminum oxide buffer. The smooth foundation allowed a high-κ hafnium oxide dielectric to grow on top while shielding the channel from harmful interactions. Devices with roughly 100-nanometer channels reached a maximum transconductance of 0.45 mS/μm with a dielectric scaled to about one nanometer equivalent oxide thickness, along with low leakage current and minimal hysteresis.

Because the transistors were built from CVD-grown material — rather than flakes peeled off a crystal in the lab — the work is closer to the wafer-scale processes real chip factories would need; uniform MoS2 growth has already been demonstrated on 12-inch wafers. The authors stress it is not yet a manufacturing solution: repeatability, durability, and process compatibility still require work.

"For many years, efforts to improve atomically thin transistors have largely focused on discovering better semiconductor materials," said Wen-Hao Chang, the study's corresponding author from NYCU. "Our research shows that the atomic interface between materials can be just as important." Co-corresponding author Tsung-En Lee added: "When transistor components become only a few atomic layers thick, the interface is no longer simply the boundary between materials; it becomes an active part of the device."

Sources