Solid-state thermal transistor for better heat management

Researchers from UCLA have developed a stable and fully solid-state thermal transistor that uses an electric field to control a semiconductor device’s heat movement. The research findings, published in Science magazine, detailed how the device works and its potential applications. The transistor could facilitate developments in the heat management of computer chips, due to its atomic-level design and molecular engineering. The advance could also further the understanding of how heat is regulated in the human body.

Study co-author Yongjie Hu said the precision control of how heat flows through materials has been studied by physicists and engineered for many years. “This new design principle takes a big leap toward that, as it manages the heat movement with the on-off switching of an electric field, just like how it has been done with electrical transistors for decades,” Hu said.

Electrical transistors were first developed by Bell Labs in the 1940s and have three terminals — a gate, a source and a sink. When an electrical field is applied through the gate, it regulates how electricity (in the form of electrons) moves through the chip. These semiconductor devices can amplify or switch electrical signals and power. But as they continue to shrink in size, billions of transistors can fit on one chip, resulting in more heat generated from the movement of electrons, which affects chip performance. Conventional heat sinks passively draw heat away from hotspots, but it is challenging to find a more dynamic control to regulate heat.

The new thermal transistor, which features a field effect (the modulation of the thermal conductivity of a material by the application of an external electric field) and a full solid state (no moving parts), also offers high performance and compatibility with integrated circuits in semiconductor manufacturing processes. The transistor’s design also incorporates the field effect on charge dynamics at an atomic interface to allow high performance using negligible power to switch and amplify a heat flux continuously.

The UCLA team demonstrated electrically gated thermal transistors that achieved high performance with a switching speed of more than 1 megahertz, or one million cycles per second. They also offered a 1300% tunability in thermal conductance. Co-author Paul Weiss said the researchers were able to leverage their understanding of molecules and interfaces to take a step forward in the control of important materials properties, with the potential for real-world impact. “We have been able to improve both the speed and size of the thermal switching effect by orders of magnitude over what was previously possible,” Weiss said.

In the team’s design, a self-assembled molecular interface is fabricated and acts as a conduit for heat movement. Switching an electrical field on and off through a third-terminal gate controls the thermal resistance across the atomic interfaces and thereby allows the heat to move through the material with precision. The transistor’s performance was validated with spectroscopy experiments and first-principles theory computations that accounted for the field effects on the characteristics of atoms and molecules.

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