Toward applications of near-field radiative heat transfer with micro-hotplates

Abstract

AbstractBringing bodies close together at sub-micron distances can drastically enhance radiative heat transfer, leading to heat fluxes greater than the blackbody limit set by Stefan–Boltzmann law. This effect, known as near-field radiative heat transfer (NFRHT), has wide implications for thermal management in microsystems, as well as technological applications such as direct heat to electricity conversion in thermophotovoltaic cells. Here, we demonstrate NFRHT from microfabricated hotplates made by surface micromachining of $$\hbox {SiO}_2$$ SiO 2 /$$\hbox {SiN}$$ SiN thin films deposited on a sacrificial amorphous Si layer. The sacrificial layer is dry etched to form wide membranes ($${100}\,\upmu \hbox {m} \times {100}\,\upmu \hbox {m}$$ 100 μ m × 100 μ m ) separated from the substrate by nanometric distances. Nickel traces allow both resistive heating and temperature measurement on the micro-hotplates. We report on two samples with measured gaps of $${610}\,\hbox {nm}$$ 610 nm and $${280}\,\hbox {nm}$$ 280 nm . The membranes can be heated up to $${250}\,^{\circ }\hbox {C}$$ 250 ∘ C under vacuum with no mechanical damage. At $${120}\,^{\circ }\hbox {C}$$ 120 ∘ C we observed a 6.4-fold enhancement of radiative heat transfer compared to far-field emission for the smallest gap and a 3.5-fold enhancement for the larger gap. Furthermore, the measured transmitted power exhibits an exponential dependence with respect to gap size, a clear signature of NFRHT. Calculations of photon transmission probabilities indicate that the observed increase in heat transfer can be attributed to near-field coupling by surface phonon-polaritons supported by the $$\hbox {SiO}_2$$ SiO 2 films. The fabrication process presented here, relying solely on well-established surface micromachining technology, is a key step toward integration of NFRHT in industrial applications.