Nanotribology of MEMS/NEMS

Abstract

Micro-/Nano-electromechanical systems (MEMS/NEMS) are future devices that have a spectrum of applications ranging from rocket technology to biological sciences. Although MEMS devices are known for over two decades, very few categories of them are used in commercially applications due to their poor reliability. Tribological phenomena like stiction, friction, and wear are major issues affecting the reliability of contact MEMS/NEMS devices and micromotors, microgears, nanosliders, etc., are some examples in which reliability is greatly hampered by such dissipation processes. In recent years, lot of research was dedicated for improving the reliability of MEMS/NEMS through lab scale tribological studies e.g., nanotribological studies. Similar tribological studies were earlier carried out on components like magnetic storage devices, electrical connectors, etc., and were successfully tackled. Present chapter is an overview of the research done over the years to understand the phenomena like stiction, friction and wear in such devices. This chapter addresses the variety of tribological problems associated with MEMS/NEMS, tribological characterization through lab scale and in-situ techniques, and various solutions that are used for improving the reliability of such devices with respect to tribological problems.

In situ running-in wear assessment in multi-asperity nanotribology

“…14a and b show the friction and wear maps obtained when a Si 3 N 4 ball (Ø 1.5 mm) is rubbing on a 2:8 μm carbon nitride (CN 6 ) coating deposited on a polished mono-crystal (100) silicon wafer by using the PE-CVD technique [68,17]. This kind of coatings is frequently used in MEMS manufacturing [1,69,5,70,68,8]. The coating's mechanical properties were determined by the parametric identification of the stress-strain law: E f : 325 GPa, Y f : 8.75 GPa and K f : 0:253 GPa as described in Fig.…”

“…1 and details in Section 3.1), which simulates a typical MEMS tribocontact -as a comb drive for instance [1,20,5]. A Si 3 N 4 ball (Ø 1.5 mm) is mounted on a stiff lever designed as a frictionless force transducer and loaded onto a flat sample with a precisely known force using a closed loop.…”

“…In addition, this approach clearly assumes that only the mechanical component of wear occurs. This is generally true in a LFM/FFM experiment that simulates a mono-asperity contact with an AFM tip [10,21,33,34,17,35], but not any more in a real MEMS displaying many asperities [1,20,36,37,7,22,38,25,17]. In the latter case, physico-chemical aspects are superimposed on the mechanical ones.…”

“…At the micro/nanoscale wear analysis is a great challenge, especially for MEMS/NEMS devices that can be strongly affected by various surface phenomena, such as friction/stiction, micro-and nanoscopic wear, surface contamination and environmental effects [1][2][3][4][5][6][7][8]. Besides, nanowear mechanisms met in various microsystems are generally closer to the polishing process in terms of wear rate [9] than the classical mechanisms of abrasion [10], adhesion [7] or ploughing [4,11,12].…”

“…Besides, nanowear mechanisms met in various microsystems are generally closer to the polishing process in terms of wear rate [9] than the classical mechanisms of abrasion [10], adhesion [7] or ploughing [4,11,12]. This peculiar wear process mainly results from the combination of a low contact pressure and a closed multi-asperity tribocontact that acts as a triboreactor at the micro/nanoscale [13][14][15][16][17], where thermal effects [18], chemical and physico-chemical interactions [19,1,20,21,7], environment's influence [14,[22][23][24]15,19,25], and tribolayer are likely to control the tribological behavior, as a selforganization process [26,27,15,16,18,17].…”