Measurement of Thermo-Mechanical Properties of Co-Sputtered SiO2-Ta2O5 Thin Films

Date of Award


Degree Name

M.S. in Electro-Optics and Photonics


Department of Electro-Optics and Photonics


Andrew Sarangan


The durability of thin film optical interference filters, integrated in systems ranging from imaging sensors to energy-efficient IR-blocking windows, is affected by its stress. The purpose of this work is to explore the thermal stress in thin films, the result of a contrastin the coefficient of thermal expansion (CTE) between the substrate and the film. Whilemuch research is focused on thin film intrinsic stress, thermal stress should also be consideredfor systems designed for high temperature variability and for systems where the film andsubstrate material properties vary greatly.This work characterizes the coefficient of thermal expansion and the Young's Modulus of SiO2 and Ta2O5 films, common low and high-index optical materials, along with composite SiO2-Ta2O5 thin films grown by reactive co-sputtering. A model for the variation of the CTE as a function of film composition is proposed, showing general agreement with the measured data. Characterization of the thermal stress in the film-substrate system is measured using acustom-built instrument, and the Young's Modulus is verified using nano-indentation. A method for evaluating the instrument noise, and its effect on the precision of the calculated CTE and Modulus values is characterized for this instrument. A model is proposed to enhance future designs-of-experiment using this instrument.


Materials Science, Optics, Thin Films, SiO2, Ta2O5, Thermal Stress, Youngs Modulus, Coefficient of Thermal Expansion

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