Lab-on-a-chip nanomechanical study of annealing and stress-induced grain growth effects on plasticity and time-dependent deformation in sputtered Pt thin films.

Neshani, Roozbeh;Coulombier, Michaël;Depoorter, Arno;Filez, Matthias;Idrissi, Hosni;et.al.
(2025) COST Action MecaNano General Meeting 2025 — Location: Krakow, Poland (19.May.2025)

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Abstract
 Polycrystalline thin platinum films with thicknesses ranging from tens to hundreds of nanometers are used in MEMS devices owing to the desirable chemical, electrical, and mechanical properties of Pt for gas sensing, catalysis, electrodes, resistive heating, and structural/processing purposes where the film is subjected to high temperatures which inevitably affects the microstructure and in turn influences the performance of the coatings. In this work, we explore the effects of mechanical stress and elevated temperatures on the microstructure in the form of grain growth and subsequently the time-dependent mechanical behavior (creep) of Pt thin films utilizing state-of-the-art nanomechanical testing and characterization methods. Sputter deposited and freestanding dogbone patterned (lithography and XeF2 under etched) Pt films on Si wafer, with a thickness of 250 nm are uniaxially deformed under tension by UCLouvain Lab-on-Chip testing platform that employs internal stress (  ̃1 GPa) of attached Si3N4 film for actuation. Multiple structures with varied stain levels remain under tension. The stress-strain curve and its evolution over time (constant stress creep test) are obtained. Examining and tracking the as-deposited specimens reveal a shift in strain and stress at both high and minuscule strains starting immediately after the release of the freestanding structure over a long time (  ̃ a year). Stress-induced grain growth, rotation, and diffusion of the grain boundaries are the primary candidate mechanisms to explain these findings. Further investigation through scanning transmission electron microscopy and localized strain map via digital image correlation shines a light on the synergistic or competitive effect of these mechanisms. Annealing-induced grain growth prior to the application of the uniaxial tension reveals the effect of grain size and microstructure on the time-dependent behavior of Pt thin films. The results of this work would complement many advanced modeling studies that investigate grain boundary diffusion and creep (Coble creep).
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Neshani, R., Coulombier, M., Depoorter, A., Filez, M., Detavernier, C., & Idrissi, H. (2025). Lab-on-a-chip nanomechanical study of annealing and stress-induced grain growth effects on plasticity and time-dependent deformation in sputtered Pt thin films. COST Action MecaNano General Meeting 2025, Krakow, Poland. https://hdl.handle.net/2078.5/270998