invited paper for International Conference on Fracture, to be held Dec. 3-7, 2001, Honolulu, Hawaii, Hilton Hotel SUMMARY AND CONCLUSIONS Understanding the effects of surface roughness on parameters such as adhesion, friction and wear is a central question in the tribology of MEMS. By combining deflection data from interferometry with computer-based models, the use of as-fabricated MEMS test structures provides a powerful means to the assess the interfacial adhesion between rough surfaces. In this work, we fabricated polysilicon cantilevers over textured surfaces of varying nm scale roughness, and measured the interfacial adhesion of the cantilevers to the surfaces. Contrary to expectations, the effect of roughness, when increased over a large range from 3 to 12 nm rms, reduced the adhesion only by a factor of 2, instead of by a factor of 16 as expected from previous literature models. The adhesion was studied by inputting 3-D data from AFM topographs of the surfaces into a finite element code, and mating the surfaces in the computer. It was found that at small roughness values, adhesion is mainly due to van der Waals forces across noncontacting areas and is proportional to 1/(average surface separation)2. At large roughnesses, asperities that nearly bridge the gap are the dominating contributor to the adhesion. ACKNOWLEDGMENTS Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy under contract DE-AC04-94AL85000. We thank Aaron Hall for help in obtaining AFM data. REFERENCES [1] K. N. G. Fuller and D. Tabor, Proc. Roy. Soc. Lond. A. 345 327 (1975). [2] D. Maugis, J. Adh. Sc. Tech. 10 (2) 161 (1996). [3] J. A. Greenwood and J. B. P. Williamson, Proc. Roy. Soc. Lond. A. 295 300 (1966). [4] J. J. Sniegowski and M. P. de Boer, Annu. Rev. Mater. Sci. 30 297 (2000). [5] R. L. Alley, P. Mai, K. Komvopoulos and R. T. Howe, Proc. 7th Int. Conf. Solid-State Sensors and Actuators, Transducers '93, Yokohama, Japan, 1993, pp. 288-291. [6] Y. Yee, K. Chun and J. D. Lee, The 8th Int. Conf. on Solid-State Sensors and Actuators, Transducers '95, Stockholm, Sweden, 1995, pp. 206-209. [7] M. R. Houston, R. T. Howe and R. Maboudian, J. Appl. Phys. 81 (8) 3474 (1997). [8] U. Srinivasan, M. R. Houston, R. T. Howe and R. Maboudian, J. Micromech. Sys. 7 (2) 252 (1998). [9] K. Komvopoulos and W. Yan, J. Trib. 119 391 (1997). [10] K. Komvopoulos and W. Wan, J. Appl. Phys. 84 (7) 3617 (1998). [11] VLSI Technology; Vol. , edited by S. M. Sze (McGraw-Hill, New York, 1983). [12] J. A. Knapp and M. P. de Boer, J. MEMS to be submitted (2001). [13] B. D. Jensen, M. P. de Boer, N. D. Masters, F. Bitsie and D. A. LaVan, J. MEMS 10 (3) in press (2001). [14] M. P. de Boer, J. A. Knapp, T. A. Michalske, U. Srinivasan and R. Maboudian, Acta Mater. 48 (18-19) 4531 (2000). [15] M. P. de Boer, P. J. Clews, B. K. Smith and T. A. Michalske, Mater. Res. Soc. Proc., San Francisco, CA, 1998, pp. 131-136. [16] J. Israelachvili, Intermolecular and Surface Forces (Academic Press, New York, 1992).
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