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

Abstract

A novel strain-rate jump method was developed for the plane-strain bulge test and used to investigate the time-dependent deformation behavior of gold thin films in the thickness range 100-400 nm. The experimental method is based on an abrupt variation of the pressurization rate. The evaluated strain-rate sensitivity was found to be five times higher for films in freestanding condition (m 5 0.094) than for films tested on a SiN x substrate (m 5 0.020). Bulge creep tests confirmed this increased time-dependence. The observation of the surface of the freestanding films after the creep tests provided evidence of apparent grain boundary sliding taking place next to intragranular plastic deformation. The out-of-plane deformation was presumably favored by the columnar microstructure of the samples, with grains extending between both free surfaces. In the case of SiN x -supported films, grain boundary sliding was prevented by the good adhesion of gold to the SiN x substrate.

Thermally Activated Deformation Behavior of ufg-Au: Environmental Issues During Long-Term and High-Temperature Nanoindentation Testing

“…From a broader perspective, the rate-dependent behavior is in good agreement with other reports on fcc ufg materials in the literature. Reference data for pure ufg-Au itself are very rare, 41 , 42 since only a limited number of studies have been performed to date. Merle et al 41 recently found significantly higher m values for nc Au films investigated via small-scale bulge testing.…”

“…Reference data for pure ufg-Au itself are very rare, 41 , 42 since only a limited number of studies have been performed to date. Merle et al 41 recently found significantly higher m values for nc Au films investigated via small-scale bulge testing. However, there were some differences in the materials’ purity, since the tested material was highly pure and additionally in the form of a ~300-nm-thick free-standing film in nature.…”

Creep behavior of gold thin films investigated by bulge testing at room and elevated temperature

“…The occurrence of grain-boundary sliding has for instance already been reported in detail in a preliminary study at room temperature by the author. 16 The discrepancy between both room-temperature measurements most likely results from significant differences between the gold samples investigated in both studies. As a matter of fact, the earlier results were achieved on non-annealed samples, which also evidenced a much higher surface roughness, with small grain boundary grooves already present in the as-deposited condition.…”

“…14 As early as 1975, bulge testing was considered suitable for creep testing purposes 15 and several groups have since been actively using it to investigate the time-dependent deformation of thin films. [16][17][18][19][20][21][22] Some of these investigations have been performed at elevated temperatures 17,18,20,22 for the purpose of reproducing the operational conditions of the films used in microchips and MEMS. In this study, these technical possibilities are combined in a systematic way in order to characterize the time-dependent properties of gold thin films as a function of the applied pressure and temperature.…”

Modeling and Measurement of Thermal–Mechanical-Stress-Creep Effect for RF MEMS Switch Up to 200 °C

“…Meanwhile, in the previous studies, the methods for the test of the thermal-mechanicalstress effects and creep effects in MEMS structures include direct methods, such as microtension [11,13,14], nanoindentation [6,15], and indirect methods, such as optical curvature [4,16,17], voltage [18][19][20], capacitance [9,10,21], and so on. However, these methods are not suitable for DC-contact RF MEMS switches.…”