Tribological properties of Micro-Sliding Mechanism Made of Silicon

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Anisotropic etching produces microscopic regular shapes that consist of specific crystal planes. In spite of the brittleness, silicon is considered to suitable for structural material, for example sliding mechanism. However, in the design of micro-mechanism, attraction force between the contact surfaces is critical, because the surface force such as friction becomes dominant comparing with the body forces such as inertia force. Thus, the reduction or control of the friction is necessary. In this study, the properties of adhesion force that acts between silicon surfaces were made clear, and the reduction of friction by applying regular pattern on the contact surfaces, texture, was tried.Surface adhesion force was measured in normal, vacuum, and dry argon gas environments. These results show that the adhesion force decreases in vacuum as well as the deviation in the measurement becomes small. The cause of the effect is considered that the number of meniscus, water bridges between the asperities in contact, decrease in vacuum. It was found that the adsorptive activity of water molecules at the surface increase adhesion force.Applying anisotropic etching with the regular line-and-space mask pattern on the specific substrate, we obtained the surface texture, which means regular and periodic cross-sectional structure on the surface. Typically, symmetric and asymmetric V-grooves were produced with the spacing of 6-micron meter and the depth of sub-micron meter. This structure decreases the adhesion force, and as a results the friction. In addition, the directionality of the friction was observed when the symmetric V-grooves were made in contact with soft materials. In case of papers, the friction in one direction is the twice of the other direction.