Tensile and fatigue strength of ultrathin copper films

Tensile and fatigue tests of ultrathin Cu films were conducted using a micro-force testing system. Fatigue strength as a function of film thickness was measured under the constant total strain range control at a frequency of 10 Hz. The experimental results exhibit that both yield strength and fatigue lifetime are dependent on film thickness. Fatigue damage behavior in the 100 nm thick Cu films with nanometer-sized grains is different from that in the micrometer-thick Cu films with large grains observed before. A comparison of the present results with those reported in literatures is conducted. Possible fatigue strengthening mechanism in the ultrathin Cu films is discussed.