A new method to measure thermal diffusivity of a thin sample was developed using a light-irradiated ac calorimetric technique. The experimental conditions and the fundamental equations for the measurement are discussed. In principle, this method can be applied no matter how thin a sample may be. This method was tested for samples of nickel, silicon, stainless steel, and alumina in the range from 50 to 300 μm in thickness. The measured thermal diffusivities coincide satisfactorily with the values reported for bulk materials. It is concluded that this method is useful in the measurement for thin materials with a variety of thermal diffusivities, and the sample mounting is easy in comparison with other methods.

This paper describes the development of an advanced method to measure the normal-to-plane thermal conductivity of very-thin insulating films. In this method the metal film layer, which is deposited on thin insulating films, is Joule heated periodically and the ac-temperature response at the center of the metal film surface is measured by a thermo-reflectance technique. The one-dimensional thermal conduction equation of the three-layered system was solved analytically, and a quite simple and accurate approximate equation was derived. In this method, calibration factors of the thermo-reflectance coefficient were determined using the known thermal effusivity of the substrate. The present method was examined for thermally-oxidized SiO 2 films (1000-20 nm thick) on a silicon wafer. The present results of the thermal conductivity agree with those of VAMAS TWA23 within ±10%.

No abstract

ZnO thin films have been produced by reactive sputtering with different oxygen contents in the sputtering gas. As a result of transmission electronic microscopy observation, each film consist of two layers: an interfacial layer close to the substrate, with a thickness of about 200 nm, composed of very fine crystal grains and an upper layer above the interfacial layer, composed of column-shaped grains aligned along the out-plane direction. The grain diameter ranges from 35 to 100 nm depending on the oxygen partial pressure. The in-plane and out-plane thermal conductivity have been measured at room temperature. The out-plane thermal conductivity of the interfacial layer is 2.3 W m−1 K−1, independent on the oxygen partial pressure. The out-plane thermal conductivity of the upper layer is 5.4, 7.1, and 4.0 W m−1 K−1, and the in-plane thermal conductivity 4.86, 6.01, and 2.66 W m−1 K−1, for the O2 30%, 60%, and 90% ZnO film, respectively. Both out-plane and in-plane thermal conductivity decrease with the decrease of grain diameter. The thermal conductance of grain boundary has been estimated with the phonon diffusion mismatch model, and the intrinsic thermal conductivity within ZnO grains has been calculated with a cylinder-structured composite model. The result shows that the thermal conductivity of the ZnO thin films is dominated by the intrinsic thermal conductivity, which is a function of grain size.

This article describes the development of a method to measure the normalto-plane thermal conductivity of a very thin electrically insulating film on a substrate. In this method, a metal film, which is deposited on the thin insulating films, is Joule heated periodically, and the ac-temperature response at the center of the metal film surface is measured by a thermo-reflectance technique. The one-dimensional thermal conduction equation of the metal/film/substrate system was solved analytically, and a simple approximate equation was derived. The thermal conductivities of the thermally oxidized SiO 2 films obtained in this study agreed with those of VAMAS TWA23 within ±4 %. In this study, an attempt was made to estimate the interfacial thermal resistance between the thermally oxidized SiO 2 film and the silicon wafer. The difference between the apparent thermal resistances of the thermally oxidized SiO 2 film with the gold film deposited by two different methods was examined. It was concluded that rf-sputtering produces a significant thermal resistance ((20±4.5)×10 −9 m 2 ·K·W −1 ) between the gold film and the thermally oxidized SiO 2 film, but evaporation provides no significant interfacial thermal resistance (less than ±4.5 × 10 −9 m 2 · K · W −1 ). The apparent interfacial thermal resistances between the thermally oxidized SiO 2 film and the silicon wafer were found to scatter significantly (±9 × 10 −9 m 2 · K · W −1 ) around a very small thermal resistance (less than ±4.5 × 10 −9 m 2 · K · W −1 ).