Bulge fatigue testing of freestanding and supported gold films

Abstract

The bulge test was used to investigate the fatigue properties of gold thin films with a thickness between 100 and 300 nm. The membranes were pressurized at a rate of 0.2 Hz up to 10 5 times, during which their stress and strain states were continuously recorded. Gold films on a silicon nitride substrate were cyclically loaded into tension and compression. Due to the presence of the substrate, no membrane failure was observed, but the residual stress shifted from an initially tensile state to an increasingly compressive one. Typical fatigue damage mechanisms consisting of extrusions were found in some large grains. Freestanding films were cyclically loaded in pure tension until failure occurred. The data acquired during the fatigue tests show a strong ratcheting of the films, which is indicative of cyclic plastic creep. Microstructural investigations clearly show grain boundary sliding in very thin films with columnar grains extending through the thickness.

Time-dependent deformation behavior of freestanding and SiNx-supported gold thin films investigated by bulge tests

“…Provided that the grain boundaries are not perfectly orthogonal to the film plane, this apparent grain boundary sliding is likely to prompt an increase of strain similar to the one observed during the creep test. Such effect has already been observed during fatigue testing of similar columnar gold films, 18 albeit only at scarce locations where strain localization occurred. Creep results in comparison in widespread grain boundary sliding of lower magnitude.…”

“…[16][17][18] It uses a large aspect ratio (4:1) rectangular membrane, which is pressurized from one side by nitrogen gas, see Fig. 1.…”

“…They were fabricated by standard lithographic techniques, starting from a silicon wafer, see for instance. 18,20,21 The freestanding SiN x films were produced by micromachining by Silson Ltd. (Northampton, UK). The SiN x films were then coated with gold by thermal evaporation in a MED020 chamber (Balzers, Lichtenstein).…”

Cracking behavior of thin gold strip deposited on polycarbonate plate under Cyclic and stepwisely-increased tension

“…Figure 1 shows the deformation of thin metal film under tension in two cases: (a) freestanding film and (b) film bonded on the surface of substrate. When the exact mechanical properties of thin film is required, mechanical tests using freestandning films are preferable [3,4]. When a freestanding film is subjected to tension, deformation of the film is not constrained and the localized necking easily occurs.…”

Fatigue crack closure in submicron-thick freestanding copper films

“…Although several studies have been conducted on the fatigue in metallic thin films fixed on substrates [25][26][27][28][29][30][31][32] and freestanding films [33][34][35][36], fatigue crack propagation of freestanding submicron-thick films have rarely been studied [37][38][39]. Thin films have a structure with a large surface area to volume ratio, and those formed by physical vapor deposition generally consist of fine columnar grains.…”