Bimetallic nanoparticles for surface modification and lubrication of MEMS switchcontacts

Abstract

Reliability continues to be a critical issue in microelectromechanical systems(MEMS) switches. Failure mechanisms include high contact resistance(R), high adhesion, melting/shorting, and contact erosion. Little previous work has addressedthe lubrication of MEMS switches. In this study, bimetallic nanoparticles (NPs) aresynthesized using a biotemplated approach and deposited on Au MEMS switch contacts asa nanoparticle-based lubricant. Bimetallic nanoparticles are comprised of a metallic core(∼10 nm diameter gold nanoparticle) with smaller metallic nanoparticles(∼2–3 nm diameter Pd nanoparticles) populating the core surface. Adhesion and resistance(R) were measured during hot switching experiments at low(10 µA) and high (1 mA) current. The Au/Pd NP coated contacts led to reducedadhesion as compared to pure Au contacts with a compromise of slightly higherR. For switches held in the closed position at low current,R gradually decreased over tens of seconds due to increased van der Waals force and growthof the real area of contact with temporal effects being dominant over load effects. Contactbehavior transitioned from ‘Pd-like’ to ‘Au-like’ during low current cycling experiments.Melting at high current resulted in rapid formation of large real contact area, low and stableR, and minimaleffect of load on R. Durability at high current was excellent with no failure through106 hot switching cycles. Improvement at high current is due to controlled nanoscale surfaceroughness that spreads current through multiple nanocontacts, which restrictsthe size of melting regions and causes termination of nanowire growth (preventsshorting) during contact opening. Based on these results, bimetallic NPs showexcellent potential as surface modifiers/lubricants for MEMS switch contacts.