In a recent article published in Nature Communications, researchers from the United States of America introduced a novel nanoscale photonic thermal transistor designed for sub-second heat flow switching.
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Control of heat flow is crucial for thermal logic devices and thermal management, with theoretical exploration preceding limited experimental progress in actively controlling heat flow. The device described in the study is a radiative thermal transistor comprising a hot source, a cold drain, and a vanadium oxide (VOx)--based planar gate electrode.
Background
Efficient control of heat flow is a critical aspect of thermal management and thermal logic devices, with implications for various technological applications. Theoretical exploration of active heat flow control has highlighted potential enhancements in thermal management systems and thermal-based computing technologies. However, translating these concepts into practical implementations has been limited by the lack of experimental progress in nanoscale heat flow control.
Traditional thermal management approaches often rely on passive heat dissipation mechanisms, which may not offer the level of control and efficiency required for emerging technologies. As the demand for compact and energy-efficient devices continues to grow, innovative solutions enabling dynamic and precise manipulation of heat transfer processes are needed.
The Current Study
The experimental setup involved the fabricating and characterizing the nanoscale radiative thermal transistor. Two independently microfabricated devices were used. The first, the source-drain device, consisted of two silicon nitride (SiN) membranes forming the thermal emitter (source) and thermal receiver (drain) of the thermal transistor. These membranes were 250 nm thick and contained a serpentine platinum resistor serving as a heater in the source and a thermometer in the drain.
The source and drain membranes were coplanar and suspended by long beams attached to a silicon handler chip. The gap size between the source and drain was fixed at 20 μm to ensure negligible near-field radiative heat transfer effects, which become significant at smaller distances than the thermal wavelength λth (~10 μm at 300 K).
Internal tensile stresses in the membranes ensured excellent planarity and coplanarity, verified through laser scanning confocal microscopy. Additionally, shields were incorporated to attenuate heat exchange between the beams, enhancing the device's thermal performance.
The fabrication process of the source-drain device involved precise microfabrication techniques to achieve the desired membrane dimensions and structural integrity. In parallel, a gate device was fabricated, featuring a VOx-coated planar electrode positioned near the source-drain device.
The gate's dielectric properties were tunable by varying its temperature, enabling control over the radiative heat transfer between the source and drain. The gate device was designed to undergo a metal-insulator transition at a critical temperature, influencing the heat flow modulation in the thermal transistor.
Experimental measurements were conducted in a high vacuum chamber with pressure below 10-6 Torr using a custom-built nanopositioner to orient the source-drain device parallel to the gate device. The temperature of the gate was precisely controlled to observe the effects on heat transfer between the source and drain membranes.
Complementary COMSOL simulations were performed to validate the experimental results and provide insights into the thermal behavior of the nanoscale radiative thermal transistor.
Results and Discussion
The experimental investigation of the nanoscale radiative thermal transistor revealed significant advancements in heat flow control and switching times. By modulating the radiative heat transfer between the source and drain membranes through the gate device, the researchers achieved remarkable outcomes.
The proximity of the gate to the source-drain device, coupled with the gate's metal-insulator transition properties, enabled a substantial modulation of heat flow. When the gap size between the source-drain device and the gate was less than approximately 1 μm, the radiative heat transfer could be altered by up to a factor of three. This demonstrated the precise control achievable through the thermal transistor configuration and the temperature-dependent dielectric properties of the gate material.
A key finding was the exceptionally fast switching times exhibited by the nanomembrane-based thermal transistor. With switching times of around 500 ms, the device outperformed previous three-terminal thermal transistors by orders of magnitude. This rapid switching capability was attributed to the small thermal mass of the devices, highlighting the efficiency and responsiveness of the nanoscale thermal transistor in dynamically modulating heat flow.
The experimental results were further supported by detailed calculations based on fluctuational electrodynamics using SCUFF-EM. These theoretical models provided insights into the underlying mechanisms of thermal modulation in the device, corroborating the experimental observations and enhancing the understanding of the thermal behavior of the nanoscale radiative thermal transistor.
Conclusion
The study presents a novel nanoscale photonic thermal transistor capable of sub-second heat flow switching, offering unprecedented control over heat transfer processes. The device's fast switching times, enabled by its small thermal mass, open new opportunities for advanced thermal management solutions.
The research findings pave the way for future innovations in thermal logic devices and highlight the potential of nanoscale technologies in revolutionizing heat flow control.
Journal Reference
Lim, JW., et al. (2024). A nanoscale photonic thermal transistor for sub-second heat flow switching. Nature Communications. DOI: 10.1038/s41467-024-49936-