Thermal Diffusivity of Metallic Thin Films: Au, Sn, Mo, and Al/Ti Alloy

Abstract

The thermal diffusivity of Au, Sn, Mo, and Al 0.97 Ti 0.03 alloy thin films, which are commonly used in microelectromechanical (MEMs) system applications, is measured by two independent methods -the ac calorimetric and photothermal mirage methods. Both methods yield similar results of the thin-film thermal conductivity, but the uncertainty of the mirage technique is found to be relatively large because of the large temperature increase during the measurement. The measured thermal diffusivities of the thin films are generally lower than those of the same bulk material. Especially, the Al 0.97 Ti 0.03 thin film shows a pronounced thermal conductivity drop compared with bulk Al, which is believed to be mainly due to impurity scattering. Comparison of the thermal conductivity with the electrical conductivity measured by the standard four-probe technique indicates that the relation of thermal and electrical conductivities follows the Wiedemann-Franz law for the case of Au and Sn thin films. However, the Lorentz number is significantly larger than the theoretical prediction for the case of Al 0.97 Ti 0.03 and Mo thin films.

Ultrafast measurements of the interfacial spin Seebeck effect in Au and rare-earth iron-garnet bilayers

“…4(b,i)]. Prior to thermalization with the phonons, the thermal diffusivity of the electrons is large, ∼10 mm 2 /s [43], due to the small heat capacity of the electrons. So, heat diffuses rapidly across the film thickness on a timescale of C e d 2 Au / e ≈ 0.4 ps.…”

A SThM probe optimization and its time-space multi-scale modeling

“…K −2 the Lorentz number. For thin films, according to [28] , the Wiedemann-Franz law relating the ratio k th / σ 0 to temperature still holds but for a Lorentz number depending on the layer thickness and material. According to [25] , [29] , for a 50 nm thin platinum layer fabricated by electron beam-physical vapor deposition, L = 5 × 10 −8 W. .…”

Thermal properties of metallic films

“…However, many other reported studies for Au thin films display a more gradual decrease in k or a with decreasing film thickness. In particular, studies of Au thin films in Refs [53][54][55][56][57][58] report values in the range k ~ 150-250 W/ m°K for films with thickness in the range 100 nm < d < 500 nm. However, one of these studies assumes the validity of the WF law and infers k from electrical conductivity measurements [57,58].…”