Advantages and Limitations of Silicon as a Bearing Material for MEMS Applications

摘要: The useful life of rotating-sliding Si MEMS moving mechanical assembly (MEMSMMA) machine elements is short. This attributed to high wear exacerbated by coefficients friction (COF) measured during actual micromachine operation and bench-top tribometry, even under the relatively mild environmental stresses room-ambient conditions. A summary recent SEM tribometric experiments given show that are caused a variety factors related low cohesive energy density surface chemistry poly-Si, Si(100) Si(111). Compared polycrystalline diamond (PCD) films, performs poorly as bearing material. In particular, 1.8-times strength C-C bond in PCD opposed Si-Si bulk silicon translates into more than 10,000 times lower rates thermal ramping 850°C, vacuum. major difference behavior has been ascribed way interact with environment. respective material removal controlled shear-induced cracking superimposed adhesive interaction incipient linkage dangling bonds between sliding counter-faces, generated heating vacuum above desorption temperature adsorbates. magnitude COF material-specific, generally defined number distribution (high friction), reconstructed (reduced friction) or adsorbate-passivated (low bonds, function atmosphere. Even benign atmospheric environment 0.2 Torr partial pressure hydrogen gas (pH2), various crystallinities at 15 g (low) tribometer load higher significantly those 28 load. There is, however, remarkably repeatable reduction COFSi within narrow range load, just below hydrogen, indicating same type heating- sliding-catalyzed dissociative chemisorption H2 previously observed PCD. contrast PCD, deconstructed (dangling) do not seem react on cooling, leaving values. Only benefited somewhat from (pH2) terms some rate reduction. other exhibited essentially 850℃ (near 10-12 m-3/N.m, 104-times PCD), although were reduced testing room one two orders-of-magnitude. These values could be further diminished keeping lowest staying 250℃ 450℃ tribocalyctic reaction region. results indicate operating thermal-atmospheric may extend MEMS-MMAs sufficiency for practicalapplications.