Tribological properties of Micro-Sliding Mechanism Made of Silicon

各向异性蚀刻产生由特定晶面组成的微观规则形状。尽管硅很脆，但它被认为适合用作结构材料，例如滑动机构。然而，在微机械设计中，接触表面之间的吸引力是至关重要的，因为表面力如摩擦力相比于本体力如惯性力成为主导。因此，减少或控制摩擦是必要的。本研究明确了硅表面间的附着力的性质，并尝试通过在接触面上施加规则图案（纹理）来降低摩擦。在正常、真空和干燥氩气环境下测量了表面附着力。这些结果表明，在真空中的粘附力减小，以及在测量中的偏差变小。其原因被认为是在真空条件下，微凸体间的水桥弯月面数量减少。研究发现，水分子在表面的吸附活性增加了附着力，在特定的基底上采用规则的线间距掩模图案进行各向异性刻蚀，获得了表面织构，即表面具有规则的周期性横截面结构。典型地，对称和非对称V形槽以6微米的间距和亚微米的深度产生。这种结构降低了粘附力，从而降低了摩擦力。此外，当对称V形槽与软材料接触时，观察到摩擦的方向性。在纸张的情况下，一个方向的摩擦力是另一个方向的两倍。

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.