Breakthrough: ±2.5V Thermal Transistor Revolutionizes Heat Flow Control

Electrically-Controlled Transistor for Thermal Energy

Researchers at UCLA have developed an electrically-controlled transistor for thermal energy, achieving a heat-flow on-off ratio of greater than 13:1 when controlled with a ±2.5V base bias at room temperature.

The voltage-flow curve of the transistor is nearly linear, and it has been successfully operated at a frequency of 1MHz.

"Precision control of heat flow through materials has long been a dream for physicists and engineers," said Professor Yongjie Hu, an engineering professor at UCLA. "This design principle represents a significant step towards achieving that dream, as it allows for the manipulation of heat movement through the on-off switching of an electric field, similar to how electrical transistors have been used for decades."

The device is built on a nano-scale, starting with an atomically-flat gold coating on a substrate. A self-assembling mono-layer of "carboranethiol cage" molecules (9-SH-o-C2B10H11 (O9)) is then added. These molecules resemble multifaceted cages that stand up on the gold surface, attached by a single leg to the surface via a sulphur atom.

On top of this layer of cages, a sheet of single-layer graphene is placed, held approximately 1nm away from the gold surface by the cage molecules. The controlling potential bias is applied between the gold surface and a top contact above the graphene.

In operation, the atoms shared by the sulphur and gold atoms form a covalent bond, which can be weakened or strengthened under the influence of the applied electric control field. This change in bond strength alters the local thermal conductivity. A similar effect occurs at the graphene interface, but it is based on Van der Waals attraction rather than covalent bonding.

The conductivity of the transistor can vary from below 10MW/m2/K to above 130MW/m2/K. For a more detailed explanation of its operation, the research is published in the journal Science under the title "Electrically Gated Molecular Thermal Switch" (abstract available without payment).