Cavity-free micro thermoelectric energy harvester with Si nanowires

We present a new design of silicon-based micro-thermoelectric generator, which utilizes silicon nanowires as the thermoelectric leg. It is driven by a steep temperature gradient exuding around a heat flow perpendicular to the substrate, and the silicon nanowires are not suspended on a cavity etched on the substrate. The power density is scalable by shortening the silicon nanowire to sub-μm length, which was experimentally demonstrated and tens of µW/cm²-class power generation was achieved at an externally applied temperature difference of only 5 K. A numerical discussion shows that the thermoelectric power can be drastically enhanced by suppressing the thermal resistance at the entire substrate. Thus, there is a plenty of room at the micro- or submicrometric scales for realizing thermal energy harvesting devices with high power densities.