Volume 26, Issue 3 (May 1998)
Piezo-Actuated Microtensile Test Apparatus
The design and performance of a microtensile test device designed for measuring the mechanical properties of thin films are reported. The moving grip is cantilevered to avoid friction. Piezoelectric actuation allows precise control of the applied tension. Force is measured indirectly using an eddy-current sensor near a flexible measuring beam, and grip displacement is measured using two similar displacement sensors. The apparatus is constructed for use with specially designed specimen assemblies in which the thin film to be tested is suspended across a silicon frame. The apparatus is rigid enough that the frames can be cut without applying tension to the thin-film tensile specimen. The tester is run in closed-loop control through a laboratory computer, which records force, displacement, and other parameters 5 times per second. Key capabilities are: stroke, 50 μm; maximum force, 1 N; minimum cycle time, 2 s; displacement resolution, ± 20 nm; and force resolution, ± 200 μN.