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

摘要

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 similar to 60 nm thick from the growth interface and the subsequent formation of columnar grains of width similar to 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.