A study of wear on MEMS contact morphologies

Abstract

The fabrication of many micro electro mechanical systems (MEMS) is mainly based on silicon and its compounds and, for moving structures such as micromotors, tribological behaviour plays a key role in the performance. In this paper the wear of MEMS-compatible materials has been investigated for a range of contact areas and contact forces typical of MEMS. Special test specimens incorporating a range of micromachined micro structures on their top surfaces have been fabricated in order to simulate those conditions. These single crystal silicon (SCS) micro structures were coated with a range of materials used in MEMS; diamond-like carbon (DLC), silicon nitride (Si3N4), silicon dioxide (SiO2), and doped and undoped polysilicon. A specimen-on-disc arrangement (a development of the macroscopic pin-on-disc) was used for the wear experiments and dead weight loading was applied using micro loads specially calibrated for this purpose. The results show that the wear rates of DLC and SCS sliding on DLC decrease with increasing sliding distance whereas Si3N4 and SiO2 showed approximately linear wear behaviour. The effect of contact morphology and contact pressure was investigated for doped polysilicon sliding on DLC and for doped and undoped polysilicon sliding on Si3N4. The results can be attributed to the differing mechanical and chemical properties of the materials leading to wear mechanisms ranging from asperity fracture to asperity deformation.

Microtribological studies of unlubricated sliding Si/Si contact in air using AFM/FFM

“…Microactuators (microturbines, micromotors, microvalves, microtools, etc.) produced by microstructure technology include solid surfaces that interact and move relative to one another, with the dimensions of such components being in the range of a few 100/zm only and those of individual structures much less than that [4][5][6]. Many micromechanical components are based on monocrystalline, or less frequently on polycrystalline, silicon and often combined monolithically with microelectronic devices to produce sophisticated microsystems.…”

MEMS Reliability Review

“…Polysilicon, a very commonly used structural material in MEMS, exhibits high friction and poor wear properties at polysilicon-polysilicon interfaces [51]- [55]. It has been demonstrated that humidity is a strong factor in the wear of rubbing surfaces in polysilicon microfabrication.…”

Diamond, Diamond-Like Carbon (DLC) and Diamond-Like Nanocomposite (DLN) Thin Films for MEMS Applications

“…Due to very low coefficient of friction and surface roughness of DLC and DLN films, the films can be act as a excellent solid lubricants of microgears or microengine based MEMS devices. Very small surface roughness can reduce the friction and wear rate in microstructure component during operations [54][55][56]. DLC coating which can improve the lifetime of linear motor actuated by electrostatic force which drive by sliding component laterally [55].…”