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

这项研究描述了用扫描探针显微镜(SPM)对电子和MEMS器件中使用的微尺度材料进行的微尺度拉伸测试。采用了单晶硅(Si)、类金刚石碳和坡莫合金薄膜三种材料。采用微机械加工技术制备了薄膜样品。此外，还研制了一种紧凑型拉伸试验机，其中包括一个较小尺寸的压电驱动器，该试验机是在SPM中建立的，由于试件的量规长度较短，在拉伸试验过程中测量微尺寸试件的应变一直是困难的。本研究使用SPM作为微尺度样品的伸长计，其分辨率为1纳米，在测试过程中获得了应变，用SPM测得的微尺度硅样品的杨氏模数范围为157~166 GPA，与毫米尺度的硅样品的杨氏模数相近。此外，用样条法对SPM数据进行拟合，重新计算出Si的杨氏模数为170 Gpa，与体硅的杨氏模数在[110]方向上一致。由于微米硅试件的抗拉强度为0.9-1.2 Gpa，是体硅的2-3倍，因此微米级试件的抗拉强度得到了提高。扫描电子显微镜观察也揭示了微尺度硅样品在室温下的脆性断裂方式。因此，试件尺寸对拉伸强度的影响可能是由于试件中裂纹的数量随着试件尺寸的减小而减少所致。本研究还对沉积在微米级硅试件上的类金刚石薄膜和坡莫合金薄膜进行了拉伸测试。然而，DLC和坡莫合金薄膜的应力-应变曲线并不准确，因为薄膜试件没有在试件的计量部断裂。还需要进一步的实验来揭示DLC和坡莫合金薄膜的力学性能。

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.