Patton Steven T, Slocik Joseph M, Campbell Angela, Hu Jianjun, Naik Rajesh R, Voevodin Andrey A
University of Dayton Research Institute, Dayton, OH 45469-0168, USA.
Nanotechnology. 2008 Oct 8;19(40):405705. doi: 10.1088/0957-4484/19/40/405705. Epub 2008 Aug 26.
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 addressed the lubrication of MEMS switches. In this study, bimetallic nanoparticles (NPs) are synthesized using a biotemplated approach and deposited on Au MEMS switch contacts as a 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 reduced adhesion as compared to pure Au contacts with a compromise of slightly higher R. 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 growth of the real area of contact with temporal effects being dominant over load effects. Contact behavior 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 stable R, and minimal effect of load on R. Durability at high current was excellent with no failure through 10(6) hot switching cycles. Improvement at high current is due to controlled nanoscale surface roughness that spreads current through multiple nanocontacts, which restricts the size of melting regions and causes termination of nanowire growth (prevents shorting) during contact opening. Based on these results, bimetallic NPs show excellent potential as surface modifiers/lubricants for MEMS switch contacts.
可靠性一直是微机电系统（MEMS）开关中的关键问题。失效机制包括高接触电阻（R）、高粘附性、熔化/短路以及接触侵蚀。此前很少有工作涉及MEMS开关的润滑。在本研究中，采用生物模板法合成双金属纳米颗粒（NPs），并将其作为基于纳米颗粒的润滑剂沉积在金MEMS开关触点上。双金属纳米颗粒由一个金属核（直径约10纳米的金纳米颗粒）组成，其核心表面分布着较小的金属纳米颗粒（直径约2 - 3纳米的钯纳米颗粒）。在低电流（10 µA）和高电流（1 mA）的热开关实验中测量了粘附力和电阻（R）。与纯金触点相比，涂覆有金/钯纳米颗粒的触点导致粘附力降低，但代价是R略高。对于在低电流下保持闭合位置的开关，由于范德华力增加以及接触实际面积的增长，R在数十秒内逐渐降低，此时时间效应比负载效应更占主导。在低电流循环实验中，接触行为从“类钯”转变为“类金”。高电流下的熔化导致快速形成大的实际接触面积、低且稳定的R，并且负载对R的影响最小。高电流下的耐久性极佳，经过10⁶次热开关循环也没有失效。高电流下的改善归因于可控的纳米级表面粗糙度，它使电流通过多个纳米接触点扩散，限制了熔化区域的大小，并在触点断开期间导致纳米线生长终止（防止短路）。基于这些结果，双金属纳米颗粒作为MEMS开关触点的表面改性剂/润滑剂显示出优异的潜力。
