While tribopolymer is usually formed due to organic-molecule polymerization under contact surface friction and is used to lubricate and to protect the surfaces of mechanical gears, it is also considered as a major source of contamination to Micro-electro-mechanical system and Nano-electro-mechanical system (MEMS and NEMS) transistors. MEMS and NEMS, designed with mechanical switching motions to overcome the problem of open-circuit voltage induced power consumption from traditional field-effect transistors, can be considered as promising potential candidates to replace current generation transistors. However, device failure occurs usually due to adsorption of ambient molecules onto device contact surfaces following stress-confined surface catalytic reactions to form tribopolymers, which are usually insulating and sticky. Experimental results only justify that the tribopolymer could be hydrocarbon chains, but detailed composition and formation mechanism remain unclear. Here, we conduct density functional theory calculations to systematically and comprehensively investigate both the initial condition of MEMS and NEMS devices contact surfaces when exposing the contamination gas molecules (particularly benzene) and model the mechanical switching cycles among three classes of conducting materials: transition metals (Pt and Au), metal oxides (RuO<sub>2</sub>) and metal sillisides (Pt<sub>x</sub>Si). We found that the tribopolymerization mechanism relies on surface catalytic effect enhanced by local confined stress, and a general set of features could be extracted for those materials: (i) chemisorption; (ii) dehydrogenation; (iii) polymerization. In particular, the applied normal stress lowers both the adsorption barrier and the reaction barriers leading to tribopolymerization. In addition, the weaker the initial binding strength of adsorbates, the less the polymerization. With the knowledge acquired in our study, we are able to provide criteria for screening and designing tribopolymer-suppressing materials and stimulate the development of MEMS and NEMS to eventually reach practical manufacturing and launch a new computing paradigm.

First-principles modeling of the joint influences of catalysis and mechanical stress in tribopolymer formation

255th National Meeting (2018)

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