Study On Evaluation Of Test Technology On Heat Transport Characteristics Of Nano Films And Interfaces By Frequency-domain Thermoreflectance Method

As the reduction in size and the increase in working frequency of electronic devices, heat management has become a critical issue. Frequency-domain thermoreflectance (FDTR), a nondestructive photothermal technique, has broad application prospects in measuring thermophysical properties of new materials, but at this stage we lack of the general evaluation of FDTR in measuring thermophysical properties.This dissertation provides the theoretical calculation and the simulation solution of FDTR experimental measurement. Based on that, assessments of FDTR test on heat transport characteristic of nanofilms and interfaces have been done, which can guide FDTR measuring thermophysical properties of new materials.Phase-frequency characteristics of properties are analysed by both continuous-wave (CW) and ultrashort-pulsed (Pulsed) type FDTR methods in two-layer and three-layer structures as well as one-dimensional (1D) and three-dimensional (3D) models. Properties principally involve the film thickness, radius of pump laser, pump-probe spot size ratio, thermal effusivity ratio, interfacial thermal conductance, thermal conductivity and the anisotropy coefficient. The result can provide guidance for thin-film material design and its thermophysical properties measurement. The applicable scope of the1D model is also obtained, which can simplify the solving process following the thermophysical properties measurement.After comparing phase-frequency characteristic curves of CW type FDTR and Pulsed type FDTR, we find that the1D or3D model results of both the two FDTR methods agree with each other at low frequency, and the CW or Pulsed type FDTR results of3D model agree with1D model at high frequency. Meanwhile, a discontinuous phenomenon is found in1D model of Pulsed type FDTR method at ultra-high frequency, but it does not appear in the3D model case.The characteristic sensitivity is proposed to describe the features of the sensitivity curves. Through the sensitivity analysis, we compare characteristic sensitivities of the two FDTR methods and provide the theory basis for choosing the appropriate FDTR method in layered structures. For example, after defining critical sensitivity, the appropriate FDTR method and the range of measured materials in the sensitivity way are given while the thermal conductivity and the interfacial thermal conductance are0.1～103W·m-1·K-1and1～104MW·m-2·K-1, respectively.Basically, by the fitting and comparison, the Al film-nanofilm-Si substrate structure and the CW type FDTR, we find that the thermal conductivity range of measured nanofilms agrees with the range of characteristic sensitivity. In other words, the measurement becomes more accurate with small thermal conductivity and large film thickness. When relative errors for nanofilm CW type FDTR fitting is less than1%, the characteristic sensitivity is approximately more than0.042. This study also showed the relation between the range of thermal conductivity and the two interfacial thermal conductances in the Al film-nanofilm-Si substrate structure when the thickness and the thermal conductivity of the nanofilm are1～300nm and0.5～500W·m-1·K-1, respectively.