Korean team builds modular transistor from a single thin film

The science ministry said Thursday that a Korean research team has developed a method to carve insulating, semiconductor and semimetallic regions out of a single two-dimensional thin film by selectively substituting the atoms that make it up, a step toward stacking next-generation chips.

The work was led by Cho Moon-ho, director of the van der Waals quantum materials research group at the Institute for Basic Science and a distinguished professor at Pohang University of Science and Technology. The team's modular transistor fabrication technique, supported by the Ministry of Science and ICT's basic science research program, was published in Science on Friday.

The team started with tungsten diselenide, in which a layer of tungsten atoms is sandwiched between layers of selenium. Keeping the tungsten in place, the researchers replaced only the selenium with oxygen, sulfur or tellurium, converting the material into tungsten oxide, an insulator, tungsten disulfide, an n-type semiconductor, and tungsten ditelluride, a semimetal.

Applied as a contact layer, the semimetal lowered the energy barrier that charge carriers must cross to 35.5 millielectronvolts, about a third of the barrier produced when a metal electrode is bonded directly to the semiconductor. The gate voltage needed to change the current tenfold was 61.3 millivolts, close to the theoretical room-temperature minimum of about 60 millivolts, and the ratio between the on and off states exceeded 10 million.

The tungsten oxide insulating film reached an equivalent oxide thickness of less than 1 nanometer, meeting a core performance target for ultrasmall devices set out in the International Roadmap for Devices and Systems. Stacking p-type and n-type transistors vertically, the team also built a complementary inverter that switched signals at a supply voltage of 1 volt, indicating the approach can be extended beyond individual devices to stacked integrated circuits.

Cho said the research matters because it applies the tools of basic materials science, the manipulation of matter at the atomic scale, to modern semiconductor technology, opening a route to a qualitative advance in future chips. He added that the technique could be extended to ultralow-power and ultrasmall semiconductors, as well as to next-generation stacked device technologies.

The team plans to apply the method to a wider range of 2D semiconductor materials and to develop it into wafer-scale, large-area processing, while exploring uses in three-dimensional stacked integrated circuits and other next-generation low-power devices.