Microfrictional Properties of Titanium Carbide
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A8.6.1
Microfrictional Properties of Titanium Carbide
Syed Imad-Uddin Ahmed, Giuseppe Bregliozzi, and Henry Haefke Micro and Nanomaterials Section CSEM Swiss Center for Electronics and Microtechnology, Inc. CH-2007 Neuchâtel, Switzerland ABSTRACT The tribological issues associated with silicon-based microelectromechanical systems (MEMS) are well known. A popular solution to improve the tribological behavior is to apply different kinds of thin films. One film material, shown to have favorable properties in specialty applications, and which may also be suited for MEMS, is titanium carbide (TiC). This paper examines the microfrictional properties of titanium carbide surfaces with two surface roughnesses sliding against polished 2 mm diameter TiC counterbodies. A comparison of the microfrictional behavior is made with various other surfaces sliding against the same material. Results indicate that the microfriction of smooth TiC sliding against a smooth TiC surface is low and similar to silicon or TiC sliding against a hydrophobic self-assembled monolayer. However, friction increases when the polished TiC ball slides against a rough TiC surface. Experiments at various relative humidities show that friction increases with increase in the relative humidity for two smooth TiC surfaces sliding against one another, but is reduced at higher relative humidity if the surface of one of the sliding partners is considerably rough. This microfrictional study shows that TiC is well suited for microtribological applications. However, for optimal performance, the surface characteristics need to be tailored to the operating conditions. INTRODUCTION The adhesion, stiction, friction and wear problems affecting many microelectromechanical systems (MEMS) during fabrication as well as during operation are well known [1]. A main reason for these problems is the preferred use of silicon, which has poor tribological characteristics [2]. Other materials, such as polycrystalline diamond [3] and amorphous diamond [4], show considerable potential. However, the popularity of silicon micromachining will ensure its utilization as a MEMS material, at least for the near future. Thus, current solutions for improved MEMS tribology is the application of thin films to overcome the detrimental tribological effects associated with silicon. Given that fact that surface forces play an important role in microsystems, coatings have been developed with the specific objective of reducing the effects of such forces. Among the surfaces forces, a great deal of attention has been focused on capillary forces, which arise due to the presence of a thin water layer on most air-exposed microsystem surfaces [5]. The effect of this water layer on adhesion and friction in the micro and nanoscale has been extensively investigated by many groups (see Ref. [5], which also explains the differences between the various tribological regimes, and references therein). Considerable efforts to overcome the negative effects of capillarity are concentrated on the application of thin hydr
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