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Researchers invent first-of-its kind solid-state thermal transistor

Republished By Plato
Republished By Plato

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Nov 08, 2023 (Nanowerk News) Researchers from UCLA have unveiled a first-of-its-kind stable and fully solid-state thermal transistor that uses an electric field to dynamically control heat dissipation, to revolutionize future semiconductor electronics, 3D IC packaging, and chiplet design. Science magazine published the group’s study (“Electrically gated molecular thermal switch”), detailing how the device works and its potential applications. With top speed and performance, the transistor could open new frontiers in heat management of computer chips through an atomic-level design and molecular engineering. The new invention may transform future technology framework for thermal management of power electronics and 3D chips. “The precision control of how heat flows through materials has been a long-held but elusive dream for physicists and engineers,” said study leader Yongjie Hu, a professor of mechanical and aerospace engineering at the UCLA Samueli School of Engineering. “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.” Electrical transistors are the foundational building blocks of modern information technology. They 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 over the years, billions of transistors can fit on one chip, resulting in more heat generated from the movement of electrons, which affects chip performance. The heating issue worsens in wide-bandgap semiconductors and 3D integrated circuits, becoming a significant bottleneck challenge. Conventional heat sinks passively draw heat away from hotspots; however, finding a dynamic control method to actively regulate heat remains a challenge. Illustration of a UCLA-developed solid-state thermal transistor using an electric field to control heat movement Illustration of a UCLA-developed solid-state thermal transistor using an electric field to control heat movement. (Image: H-Lab) While there have been efforts in tuning thermal conductivity, their performances have suffered due to reliance on moving parts, ionic motions, or liquid solution components. This has resulted in slow switching speeds for heat movement on the order of minutes or far slower, creating issues in performance reliability as well as incompatibility with semiconductor manufacturing. The new thermal transistor, which boasts 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), offers high performance and compatibility with integrated circuits in semiconductor manufacturing processes. Their design incorporates the field effect on charge dynamics at an atomic interface to allow unprecedented performance using a negligible power to continuously switch and amplify a heat flux. The UCLA team demonstrated electrically gated thermal transistors that achieved record-high performance with switching speed of more than 1 megahertz, or 1 million cycles per second. They also offered a 1,300% tunability in thermal conductance and reliable performance for more than 1 million switching cycles. This performance represents the highest values for solid-state thermal devices at several orders of magnitude over the previously reported best results. “This work is the result of a terrific collaboration in which we are able to leverage our detailed understanding of molecules and interfaces to make a major step forward in the control of important materials properties with the potential for real-world impact,” said co-author Paul Weiss, a professor of chemistry and biochemistry. In their proof-of-concept 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 thus heat moves through the material with precision. The researchers validated the transistor’s performance with spectroscopy experiments and conducted first-principles theory computations that accounted for the field effects on the characteristics of atoms and molecules.
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