Lubrication of Microelectromechanical Devices Using Liquids of Different Viscosities

Abstract

Lubrication of contacting and sliding surfaces in MEMS (microelectromechanical systems) is particularly challenging because of the predominance of surface forces at the microscale. The current paper explores the possibility of using liquid lubrication in this application. Measurements of friction and lubricant film thickness have been made for liquid lubricants of different viscosities, including low viscosity silicone oil, hexadecane, squalane, and water. Testing was carried out using a newly developed MEMS tribometer in which a rotating silicon disk is loaded against a stationary silicon disk. Two different test setups were used: one where both disks are flat, and the other where the stationary disk is structured as in a thrust pad bearing. In all tests the disks were fully submerged in the lubricant. With the flat-on-patterned disk combination, the variation of friction with rotation speed was found to follow classical Stribeck curves for all the lubricants tested. The friction at high speeds also decreased with increasing normal load, in accordance with hydrodynamic lubrication theory. For the least viscous lubricants, it was found that the hydrodynamic friction coefficients remained relatively low even at higher speeds. In particular, for water the friction coefficient for water was around 0.1 at 10,000 rpm. However, boundary friction was found to be unacceptably high at low speeds where there was insufficient lubricant entrainment. The experimental results have been compared with a finite difference solution of Reynolds equation and reasonable agreement is seen between theory and experiment. The results indicate that liquid lubrication is potentially an effective means of lubricating MEMS components with high levels of sliding.

Confining Liquids on Silicon Surfaces to Lubricate MEMS

“…The two liquid lubricants tested were water and hexadecane, since these have sufficiently low viscosities to give low friction in hydrodynamically lubricated MEMS contacts [6,[8][9][10].…”

“…This was initially ignored in MEMS due to the assumption that viscous drag forces would be too high [7]. However, it has been shown that liquid lubrication is effective at controlling friction and wear in MEMS, provided very low viscosity lubricants are used [8]. Furthermore, the fluid film (i.e.…”

Macroscopic scattering of cracks initiated at single impurity atoms

“…Furthermore, our results suggest that 3PB experiments on intrinsic specimens could be used to identify the minimum speed for smooth cleavage during brittle fracture propagation, and that substitutional impurity content is one of the factors controlling the roughness of cleavage surfaces and, as such, should be taken into account when operatively defining the fracture toughness of crystalline specimens. At a more practical level, crystalline surface samples hosting asperities with finely controlled slope, height and spacing could be useful in experiments carried out to calibrate adhesion/friction models 31,32 , or to tune the interfacial properties that govern boundary and mixed lubrication in tribological applications in MEMS 33 .…”

Advanced Nanomechanical Test Techniques

“…Table 3 summarizes the key differences between the techniques. Small scale fretting of ta-C films on Si Wear and adhesion limit the practical usability of silicon-based devices and several approaches are being considered to overcome that problem including liquid lubrication [89], solid lubrication with self-assembled monolayers [90] and a variety of thin films [91][92][93]. In [48] small scale fretting of 5, 20 and 80 nm thickness ta-C films deposited on Si(100) was investigated using spherical indenters.…”