Thermal conductivity measurements of sub-surface buried substrates by steady-state thermoreflectance

Md Shafkat Bin Hoque; Yee Rui Koh; Kiumars Aryana; Eric R Hoglund; Jeffrey L Braun; David H Olson; John T Gaskins; Habib Ahmad; Mirza Mohammad Mahbube Elahi; Jennifer K Hite; Zayd C Leseman; W Alan Doolittle; Patrick E Hopkins

doi:10.1063/5.0049531

Thermal conductivity measurements of sub-surface buried substrates by steady-state thermoreflectance

Rev Sci Instrum. 2021 Jun 1;92(6):064906. doi: 10.1063/5.0049531.

Affiliations

¹ Department of Mechanical and Aerospace Engineering, University of Virginia, Charlottesville, Virginia 22904, USA.
² Department of Materials Science and Engineering, University of Virginia, Charlottesville, Virginia 22904, USA.
³ School of Electrical and Computer Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332, USA.
⁴ Department of Electrical and Computer Engineering, University of New Mexico, Albuquerque, New Mexico 87131, USA.
⁵ U.S. Naval Research Laboratory, Washington, DC 20375, USA.
⁶ Department of Mechanical Engineering, King Fahd University of Petroleum and Minerals, Dhahran, Eastern Province 31261, Saudi Arabia.

PMID: 34243549
DOI: 10.1063/5.0049531

Abstract

Measuring the thermal conductivity of sub-surface buried substrates is of significant practical interests. However, this remains challenging with traditional pump-probe spectroscopies due to their limited thermal penetration depths. Here, we experimentally and numerically investigate the TPD of the recently developed optical pump-probe technique steady-state thermoreflectance (SSTR) and explore its capability for measuring the thermal properties of buried substrates. The conventional definition of the TPD (i.e., the depth at which temperature drops to 1/e value of the maximum surface temperature) does not truly represent the upper limit of how far beneath the surface SSTR can probe. For estimating the uncertainty of SSTR measurements of a buried substrate a priori, sensitivity calculations provide the best means. Thus, detailed sensitivity calculations are provided to guide future measurements. Due to the steady-state nature of SSTR, it can measure the thermal conductivity of buried substrates that are traditionally challenging by transient pump-probe techniques, exemplified by measuring three control samples. We also discuss the required criteria for SSTR to isolate the thermal properties of a buried film. Our study establishes SSTR as a suitable technique for thermal characterizations of sub-surface buried substrates in typical device geometries.