Improved micro-contact resistance model that considers material deformation, electron transport and thin film characteristics

This paper reports on an improved analytic model forpredicting micro-contact resistance needed for designing microelectro-mechanical systems (MEMS) switches. The originalmodel had two primary considerations: 1) contact materialdeformation (i.e. elastic, plastic, or elastic-plastic) and 2) effectivecontact area radius. The model also assumed that individual aspotswere close together and that their interactions weredependent on each other which led to using the single effective aspotcontact area model. This single effective area model wasused to determine specific electron transport regions (i.e. ballistic,quasi-ballistic, or diffusive) by comparing the effective radius andthe mean free path of an electron. Using this model required thatmicro-switch contact materials be deposited, during devicefabrication, with processes ensuring low surface roughness values(i.e. sputtered films). Sputtered thin film electric contacts,however, do not behave like bulk materials and the effects of thinfilm contacts and spreading resistance must be considered. Theimproved micro-contact resistance model accounts for the twoprimary considerations above, as well as, using thin film,sputtered, electric contact

Investigating the functionalisation of poly-ether-ether-ketone surfaces through the application of surface texturing for friction and wear control within all polymeric joint prosthesis

This thesis investigates the application of surface textures applied to an un-filled poly-ether-ether-ketone (PEEK) surface via laser ablation for the purpose of friction and wear control. Surface functionalisation was demonstrated by the manipulation of surface characteristics via texturing. Improving surface wettability characteristics showed that increasing surface hydrophilicity improved the surfaces’ friction and wear performance. Within durability tests a novel approach, in the form of acoustic emissions (AE), was employed to monitor tribological activity within an all PEEK sliding couple. AE output was correlated with individual strokes throughout the test and the magnitude and frequency of the captured AE signal was used to ascertain an understanding of tribological phenomena occurring within the tribo-system. Texture parameters were investigated, showing a diameter/depth combination of 50µm and 20µm respectively were optimum for friction reduction when dispersed over the surface at a density of 20%. Friction reduction for textured surfaces was attributed, in part, to the generation of hydro-dynamic lift. To verify hydrodynamic behavior, the system was modeled using the Reynolds equation, and the viscous friction was computed and compared to empirical results. Good agreement across diameters and aspect ratio were captured however, the depth showed to vary considerably for shallower pores of smaller diameter. Durability tests, showed that a textured surface outperformed an un-textured surface by 3 times. The primary mechanism contributing to the low friction and wear of textured surfaces was the retention of fluid within the contact zone and the reduction in abrasive wear particles through the wear trapping capabilities of the textured pores