New development of compact tensile tester with scanning probe microscope for micro-scale specimen

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This research describes a micro-scale tensile test with a scanning probe microscope (SPM) for micro-scale materials used in electronic and MEMS devices. Three kinds of materials, which are single crystal silicon (Si), diamond like carbon and permalloy thin films, was used here. The film specimens were fabricated by a micro machining process technique. A compact tensile tester including a smaller sized piezoelectric actuator was also newly developed, and the tester was built in the SPM.It has been so far difficult to measure strain of micro-scale specimen during a tensile test because of the shorter gage length of specimen. In this research, the SPM was used as an extensometer of micro-scale specimens with a resolution on the order of 1 nanometer, so that strain was obtained in the course of tests.Young's modulus of micro-scale Si specimen measured by the SPM ranged from 157 GPa to 166 GPa, which was similar to that of millimeter scale Si. Furthermore, the Young's modulus of Si recalculated by fitting the SPM data to a spline function showed 170 GPa, which was in agreement with that of bulk sized Si in [110] direction. The micro-scale specimen produced an increase of the tensile strength since the strength of micro-scale Si specimen showed 0.9-1.2 GPa that was 2-3 times larger than that of bulk sized Si. Scanning electron microscopic observations also revealed micro-scale Si specimen fractured brittle manner in room temperature. So, the specimen size effect on tensile strength would have been caused by a reduction of the number of cracks in specimen with decreasing the specimen size.This research also carried out tensile tests of DLC and permalloy thin films deposited on the micro-scale Si specimen. However, an accurate stress-strain curve of DLC and permalloy films was not obtained since the film specimen did not fractured at the gage part of specimen. Further experiments are needed to reveal mechanical properties of DLC and permalloy films.