4:00 PM - EN14.04.02
Finite Element Modelling of Optically Pumped Thermoreflectance
David Lara Ramos1,2,3,Kerry Maize4,Nicolas Perez1,Gabi Schierning1,Kornelius Nielsch1,2,Ali Shakouri4
Leibniz Institute for Solid State and Materials Research1,TU Dresden2,Consejo Nacional de Ciencia y Tecnologia (CONACyT)3,Purdue University4
Thermoreflectance microscopy is a noninvasive optical technique that is capable of mapping 2D temperature fields of surfaces with high spatial and time resolution. State of the art thermoreflectance microscopy set-ups use electrical current to thermally excite the device or sample under study and so generate temperature differences. This technique is particularly useful for investigating hot spots in integrated circuitry leading to failure or premature fatigue of microelectronic components . It is also a powerful tool for investigating thermal properties of materials [1, 2] and thermal characterization of micro thermoelectric devices . All-optical pump probe thermoreflectance microscopy, which thermally excites the sample by a pump laser spot focused on the sample’s surface, has recently been proposed as a promising tool for investigating anisotropic thermal properties of thin film hetero structures . The later research efforts motivates the technique’s further development, since thermoelectric materials often present anisotropic thermal transport properties whose experimental characterization is challenging, especially in thin films. In this work an all-optical pump probe thermoreflectance microscopy is used to study a series of thin film multilayers of TiN/AlScN deposited on MgO substrates  which present tunable anisotropy. The temperature distribution on the surface of the sample was then analyzed by the probe laser and correlated to finite element modelling (FEM) simulations. FEM allowed us to systematically analyze, using realistic parameters, the impact of various experimental factors that affect the result of measurements. We gained understanding about the required experimental conditions in order to extract cross plane and in plane thermal conductivity of the thin films. Using FEM, a measure of the sensitivity required by the experimental device was obtained.
 Maize, K. High Resolution Thermoreflectance Imaging of Power Transistors and Nanoscale Percolation Networks. PhD thesis, UC Santa Cruz. 2014.
 Ziabari, A., Torres, P., Vermeersch, B., Xuan, Yi, Cartoixà, X., Torelló, A., Bahk1, J.-H., Koh1, Y. R., Parsa, M., Ye1, P. D., Alvarez, F. X. & Shakouri, A. Full-field thermal imaging of quasiballistic crosstalk reduction in nanoscale devices. Nature communications. (2018) 9:255.
 Li, G., Garcia Fernandez, J., Lara Ramos, D. A., Barati, V., Pérez, N., Soldatov, I., Reith, H., Schierning, G. & Nielsch, K. Integrated microthermoelectric coolers with rapid response time and high device reliability. Nature Electonics. 2018, vol 1, 555–561.
 Yazawa, K., León Gil, J. A., Maze, K., Kendig, D., & Shakouri, A. Optical Pump-Probe Thermoreflectance Imaging for Anisotropic Heat Diffusion. 2018 17th IEEE Intersociety Conference on Thermal and Thermomechanical Phenomena in Electronic Systems (ITherm). 2018, 2577-0799.
 Saha, B., Koh, Y. R., Feser, J. P., Sadasivam, S., Fisher, T. S., Shakouri, A., Sands, T. D. Phonon wave effects in the thermal transport of epitaxial TiN/(Al,Sc)N metal/semiconductor superlattices. Journal of Applied Physics. 2017, 015109.