Thickness-dependent thermal conductivity of ultrathin (< 100 nm) barium titanate films

Abstract

Thin film barium titanate (BaTiO3) is a promising material in the electronics and ceramics industry owing to its compelling dielectric properties. A number of works have investigated its dielectric and structural properties, but less studied are its thermal properties particularly at sub-100 nm thicknesses. Here, we measure the room-temperature thermal conductivity of ultrathin (< 100 nm), pulsed laser deposited BaTiO3 films. The measured thermal conductivities are thickness-dependent, and this trend is consistent with the thickness-dependent crystallinity of the films. Transmission electron microscopy analysis of the films reveals the presence of an initial amorphous layer ~ 60 nm thick from the growth interface and the subsequent formation of columnar grains of width ~ 12 nm that are embedded within an amorphous matrix. For a region that incorporates grains with columnar morphology, we find that cross-plane heat conduction may be favored by 30–40% over in-plane heat conduction due to the columnar morphology of grains.