Abstract
Efficient thermal management at the nanoscale is important for reducing energy consumption and dissipation in electronic devices, lab-on-a-chip platforms and energy harvest/conversion systems. For many of these applications, it is much desired to have a solid-state structure that reversibly switches thermal conduction with high ON/OFF ratios and at high speed. Here we describe design and implementation of a novel, all-solid-state thermal switching device by nanostructured phase transformation, i.e., modulation of contact pressure and area between two poly-silicon surfaces activated by microstructural change of a vanadium dioxide (VO2) thin film. Our solid-state devices demonstrate large and reversible alteration of cross-plane thermal conductance as a function of temperature, achieving a conductance ratio of at least 2.5. Our new approach using nanostructured phase transformation provides new opportunities for applications that require advanced temperature and heat regulations.
Highlights
Actuators can deliver simultaneously high force and large stroke of actuation, as opposed to other actuation mechanisms where only one is high
The VO2-only device (VO2) thin films were grown using pulsed laser deposition on the surface of a poly-Si layer that was prepared with low-pressure chemical vapour deposition
The hydrofluoric acid (HF) vapour was utilized to etch the low-temperature silicon dioxide (LTO) entering from the side opening, causing the top poly-Si layer to collapse onto the bottom poly-Si layer with good conformation
Summary
Actuators can deliver simultaneously high force and large stroke of actuation, as opposed to other actuation mechanisms where only one is high. The TSS is mainly composed of a thin VO2 layer stacked onto a polycrystalline Si layer, with a nanogap created in the Si layer. The layers are deposited at temperatures higher than the VO2 phase transition temperature (TPT), such that at T > TPT the nanogap interface is largely conformal. As temperature is cooled across the phase transition to T < TPT, the shape change of VO2 layer pulls the neighboring Si layer away from the Si layer below that, strongly reducing the contact pressure and area between these two layers. Heat conduction across the interface is proportionally reduced. Our TSS demonstrates dramatic enhancement of the thermal-switching ON/OFF ratio, by a factor of ~6.7, compared to VO2 film devices without incorporation of the nanogap
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