13th International Conference on Fracture June 16–21, 2013, Beijing, China -9- 4. Summary In summary, the tensile specimens were anodically bonded at the relatively low temperature and voltage, using Pyrex 7740 glass and patterned crystalline silicon chips coated with Al film. To investigate the mechanical behavior of anodically bonded interlayer of Pyrex Glass/Al/Si, the tensile experiments were completed with the newly designed flexible fixtures, and the analysis for the anodically bonded intermediate layer were also made with SEM and TEM. The formation of the fractal patterns in the process of anodic bonding is due to the limited diffusion, aggregation, and crystallization of Si and Al atoms in the intermediate Al film. These fractal patterns have the fractal dimension of 2-D DLA process, and their fractal dimension is around 1.7. These fractal patterns in the intermediate Al film consist of Al and Si crystalline grains.The fractal patterns improves the bonding strength between the Pyrex 7740 glass and the Al intermediate layer coated on the crystal silicon substrate. The formation of the dendritic nanostructures is due to the diffusion and reaction near the glass/Al interface under a non-equilibrium condition during the anodic bonding process. These nanostructures might reveal helpful clues in improving the bonding quality. The dendritic nano-crystalline structures are shown to be one of the key structures for the improvement of strength in anodic bonding. Test results demonstrated that, the bonding strength increases with the bonding temperature and voltage. This is in agreement with earlier results reported in the literature. But the experiments exhibit that the tensile strength decreases with the increase of the thickness of Al intermediate layer. Although the measured bonding strength values exhibit a rather large variance around a mean value, the experimental results can be referenced qualitatively. With the dimensions of MEMS devices downward, the scale effect in anodically bonded micro anchors should be considerable during the process of device design. Acknowledgements We would like to thank Mr. Wan Lap Yeung of Hong Kong University of Science and Technology and Dr. Jijia Xie and Mr. Chuang Feng for their help during specimen preparation and tensile experiments. This work was supported by the National Natural Science Foundation of China (NSFC) (Grant No. 11272144) and the Jiangsu Provincial Natural Science Foundation of China (Grant No. BK2011725). References [1] S. Farrens. Wafer and Die Bonding Technologies for 3D Integration. In: Materials and Technologies for 3-D Integration. F. Roozeboom, C. Bower, P. Garrou, et al., Ed. Warrendale: Materials Research Society. 2009. pp. 55-65. [2] M.M. Koebel, N. El Hawi, J. Lu, et al. Anodic bonding of activated tin solder alloys in the liquid state: A novel large-area hermetic glass sealing method. Solar Energy Materials and Solar Cells. 2011, 95 (11), pp.3001-3008. [3] Z. Wang, D. Wang, N. Jiao, et al. Nanochannel system fabricated by MEMS microfabrication and atomic force microscopy. Iet Nanobiotechnology. 2011, 5 (4), pp.108-113.
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