Young’s modulus measurements and grain boundary sliding in free-standing thin metal films

Abstract

Young’s modulus of free-standing polycrystalline Al, Au, and W films with submicron thickness has been studied using a dynamic bulge-testing technique. For Au and Al films a clear frequency dependence of the modulus is observed at room temperature in the range 1×10−4–0.5 rad/s. The values of the moduli are considerably smaller than the corresponding values of bulk material. The modulus of W films measured under the same conditions does not depend on frequency and is equal to the bulk value. The origin of the behavior found in the Al and Au films is anelastic grain boundary sliding. As a consequence of the relatively small grain size of thin polycrystalline films this phenomenon is observable at room temperature in films with a relatively low melting point.

Strain rate sensitivity of nanocrystalline Au films at room temperature

“…Therefore, the reduced elastic modulus may be associated with the increased grain boundary volume that is occupied by disordered Au atoms contributing to the increased film compliance [28,29]. This argument, however, does not provide a general mechanism for nanocrystalline materials.…”

Bulge fatigue testing of freestanding and supported gold films

“…The use of a fast settling exhaust valve allows an operating frequency of 0.2 Hz, which is twice as high as that found for a bulge tester with comparable gas pressure actuation. 20 Higher frequencies are difficult to achieve with the current experimental setup, due to the limited permitted gas flow. This is the reason why the setup is preferentially used for low cycle rather than high cycle and ultrahigh cycle fatigue testing.…”

A simple electrical test method to isolate viscoelasticity and creep in capacitive microelectromechanical switches

“…5 The experimental results are a strong validation of the bipolar hold-down method for straightforward electrical analysis of mechanical effects in thin-film capacitive switches. As new materials are constantly being investigated for potential use in RF MEMS, 10,20,23,24 the authors feel that this non-destructive method will prove very useful to device designers and process engineers.…”

“…The viscoelastic effect is a fully recoverable material stress relaxation mechanism perpetuated by grain boundary sliding. 11,20 A further classification-linear viscoelasticity, requires that this modulus be independent of the magnitude of stress and strain. This means the time-dependence of material stress relaxation during a strain cycle should be equal to its recovery during a recovery cycle.…”