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

本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微尺度拉伸试验。本文使用了单晶硅、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薄膜样品。本文还研制了一种小型的压电致动器紧凑型拉伸试验机，并将其安装在SPM中。由于微尺度试样的规长较短，在拉伸试验中测量应变一直是困难的。在本研究中，SPM作为分辨率为1纳米量级的微尺度试样的延伸计，在测试过程中获得应变。SPM测量的微尺度Si试样的杨氏模量在157 ~ 166 GPa之间，与毫米尺度Si的杨氏模量相近。此外，通过将SPM数据拟合到样条函数中重新计算Si的杨氏模量为170 GPa，这与体尺寸Si在[110]方向上的杨氏模量一致。微尺度Si的抗拉强度达到0.9 ~ 1.2 GPa，是体尺寸Si的2 ~ 3倍。扫描电镜观察显示，微尺度Si试样在室温下呈脆性断裂状态。因此，试样尺寸对抗拉强度的影响可能是由于试样中裂纹数量的减少而引起的。本研究还对沉积在微尺度Si试样上的DLC薄膜和坡莫合金薄膜进行了拉伸试验。然而，由于薄膜试样没有在试样的测量部分断裂，因此没有得到DLC和坡莫合金薄膜的准确应力-应变曲线。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.