UCLA Creates First Stable, Fully Solid-State Thermal Transistor

November 21, 2023 by Darshil Patel

The transistor prototype opens doors for more efficient thermal management in integrated circuits—and even presents interesting opportunities in human metabolic research.

Researchers at UCLA have developed a solid-state thermal transistor that uses external electric fields to control heat flow at the nanoscale. In other words, the prototype acts as an electrical transistor for thermal energy.


The solid-state thermal transistor

The solid-state thermal transistor uses an electric field to manipulate heat movement. Image used courtesy of H-Lab/UCLA

The researchers claim their recently developed transistor is highly compatible with the semiconductor manufacturing process and delivers superior performance while consuming minimal electrical power to switch and amplify heat consistently.


Beating Integrated Circuit Heat

The UCLA team developed the thermal transistor to address the issue of heat generation in scaled-down integrated circuits. Heat leads to energy waste, and excessive heat can deteriorate the performance and lifespan of electronic components. Thermal management can enhance a system's efficiency and the durability of electronic components.

Conventional thermal management systems include passive devices like heat sinks, air and liquid cooling methods, thermoelectric cooling, and active thermal controls that use sensors and control systems to regulate the temperature in real time. The choice of cooling methods depends on factors like the power density of the chip, available space, cost considerations, and the required level of cooling.

Regardless of the cooling method, heat movement is usually a slow process—on the order of a few minutes—affecting the performance and reliability of the chips.


An Electrically-Gated Thermal Switch

The basic structure of the researchers' thermal transistor is analogous to the electronic transistor. The device channel connects the hot and cold thermal reservoirs, and the third terminal acts as a gate to control the thermal conductivity using an electric field. The researchers measured the device's thermal conductivity, which shows high dependence on the gate voltage.

When a gate voltage is applied from 2.5 V to -2.5 V, the device exhibits a change in thermal conductivity from 10 to 134 MW/m2K. They tested the device's reversibility between the on and off state for up to one million cycles.


Device design and thermal conductivity characteristics

Device design and thermal conductivity characteristics. Image used courtesy of UCLA

The team performed measurements to characterize thermal switching speeds using ultra-fast optical microscopy. The device's fast thermal switching is field-induced, which depends on instantaneous charge dynamics. The study reports that the switching is reversible from frequencies between 0.1 Hz and 1 MHz.


Engineering Sheds Light on Cellular Biology

The UCLA team suggests that their technology can extend beyond IC cooling and expand our understanding of heat management in the human body.

Cellular activities generate heat, and understanding the heat dynamics at the molecular level can provide information on metabolic processes. Heat also results from the folding and unfolding of proteins. If researchers can control heat flow at the molecular level, they may also be able to manipulate proteins for therapeutic purposes in the future. Since cells respond to changes in temperature, precise control of heat flow at the molecular level may enable researchers to study how cells react to temperature variations.