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The role of van der Waals forces in adhesion of micromachined surfaces

Nature Materials volume 4, pages 629–634 (2005)Cite this article

Abstract

Interfacial adhesion and friction are important factors in determining the performance and reliability of microelectro- mechanical systems. We demonstrate that the adhesion of micromachined surfaces is in a regime not considered by standard rough surface adhesion models. At small roughness values, our experiments and models show unambiguously that the adhesion is mainly due to van der Waals dispersion forces acting across extensive non-contacting areas and that it is related to 1/Dave2, where Dave is the average surface separation. These contributions must be considered because of the close proximity of the surfaces, which is a result of the planar deposition technology. At large roughness values, van der Waals forces at contacting asperities become the dominating contributor to the adhesion. In this regime our model calculations converge with standard models in which the real contact area determines the adhesion. We further suggest that topographic correlations between the upper and lower surfaces must be considered to understand adhesion completely.

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Figure 1: Cantilever fabrication process and nomenclature.
Figure 2: Interferograms of cantilever beams at an actuation voltage of Vpad = 50 V.
Figure 3: Experimental and FEM beam deflections for an actuation voltage of Vpad = 40 V.
Figure 4
Figure 5: The numerical surface-separation routine uses actual AFM images of the landing-pad and structural polysilicon layers to calculate the adhesion energy.
Figure 6: A histogram of the adhesion contributions versus pixel separation (2 nm bin size).

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Acknowledgements

Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the US Department of Energy’s National Nuclear Security Administration under contract DE AC04-94AL85000. The authors would like to thank A. Corwin for help in collecting experimental data and B. McKenzie for the SEM images.

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Authors and Affiliations

  1. Department of Mechanical Engineering, University of Colorado, Boulder, Colorado, 80309, USA

    Frank W. DelRio & Martin L. Dunn

  2. Radiation and Reliability Physics Department, Sandia National Laboratories, Albuquerque, New Mexico, 87185, USA

    Frank W. DelRio & Maarten P. de Boer

  3. Radiation-Solid Interactions Department, Sandia National Laboratories, Albuquerque, New Mexico, 87185, USA

    James A. Knapp

  4. Material Mechanics Department, Sandia National Laboratories, Albuquerque, New Mexico, 87185, USA

    E. David Reedy Jr

  5. Microelectronics Operations Department, Sandia National Laboratories, Albuquerque, New Mexico, 87185, USA

    Peggy J. Clews

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  1. Frank W. DelRio
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Correspondence to Maarten P. de Boer.

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DelRio, F., de Boer, M., Knapp, J. et al. The role of van der Waals forces in adhesion of micromachined surfaces. Nature Mater 4, 629–634 (2005). https://doi.org/10.1038/nmat1431

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