Phonon Inelastic Scattering in Ultrathin HfO2-Based Layer-by-Layer Nanostructure.

HfO2, as a kind of high dielectric ceramic material, has important applications in microelectronic devices. With device miniaturization, the intrinsic thermal conductivity and thermal boundary resistance of ultrathin HfO2 films on Si substrate are becoming increasingly important in thermal management related to heat conduction for gate dielectrics on a few nanometer scales. To study the thickness and temperature dependences of the thermal properties, a series of ultrathin HfO2 films with thickness of 2 nm, 6 nm, 10 nm and 20 nm are grown on Si substrates. The intrinsic thermal conductivities and the thermal boundary resistances are simultaneously measured by the two-color femtosecond pump–probe technique between 300 and 500 K. The intrinsic thermal conductivity of the 2 nm film is about 0.13 Wm−1·K−1, and the thermal conductivity of HfO2 is positive correlated to the thickness. The measured thermal boundary conductance is positive correlated to the temperature. The contributions of elastic and inelastic scattering is determined through the anharmonic inelastic model, and the results show that the inelastic scattering plays a nonnegligible role in interfacial thermal transport. [ABSTRACT FROM AUTHOR]