Vacuum thermal switch made of phase transition materials considering thin film and substrate effects

In the present study, we theoretically demonstrate a vacuum thermal switch based on near-field thermal radiation between phase transition materials, i.e., vanadium dioxide (VO₂), whose phase changes from insulator to metal at 341K. Strong coupling of surface phonon polaritons between two insulating VO₂ plates significantly enhances the near-field heat flux, which on the other hand is greatly reduced when the VO₂ emitter becomes metallic, resulting in strong thermal switching effect. Fluctuational electrodynamics incorporated with anisotropic wave propagation predicts more than 80% heat transfer reduction at sub-30-nm vacuum gaps and 50% at vacuum gap of 1μm. Furthermore, the penetration depth inside the uniaxial VO₂ insulator is studied at the vacuum gap of 50nm, suggesting the possible impact of reduced VO₂ thickness on the near-field thermal radiation with thin-film structures. By replacing the bulk VO₂ receiver with a thin film of several tens of nanometers, the switching effect is further improved over a broad range of vacuum gaps from 10nm to 1μm. Finally, the effect of SiO₂ substrate for the thin-film emitter or receiver is also considered to provide insights for future experimental demonstrations. By controlling heat flow with near-field radiative transport, the proposed vacuum thermal switch would find practical applications for energy dissipation in microelectronic devices and for the realization of thermal circuits.