Author's personal copy Applied Surface Science 257 (2011) 3153–3157 Contents lists available at ScienceDirect Applied Surface Science journal homepage: www.elsevier.com/locate/apsusc DLC nano-dot surfaces for tribological applications in MEMS devices R. Arvind Singh a , Kyounghwan Na a , Jin Woo Yi b , Kwang-Ryeol Lee b , Eui-Sung Yoon a,∗ a Nano-Bio Research Center, Korea Institute of Science and Technology, 39-1, Hawolgok-dong, Seongbuk-gu, Seoul 136-791, South Korea b Computational Science Center, Korea Institute of Science and Technology, 39-1, Hawolgok-dong, Seongbuk-gu, Seoul 136-791, South Korea article info Article history: Received 14 May 2010 Received in revised form 22 October 2010 Accepted 27 October 2010 Available online 3 November 2010 Keywords: Nano Micro Adhesion Friction Wear Tribology Diamond-like carbon abstract With the invention of miniaturized devices like micro-electro-mechanical systems (MEMS), tribological studies at micro/nano-scale have gained importance. These studies are directed towards understanding the interactions between surfaces at micro/nano-scales, under relative motion. In MEMS devices, the critical forces, namely adhesion and friction restrict the smooth operation of the elements that are in relative motion. These miniaturized devices are traditionally made from silicon (Si), whose tribological properties are not good. In this paper, we present a short investigation of nano- and micro-tribological properties of diamond-like carbon (DLC) nano-dot surfaces. The investigation was undertaken to evaluate the potential of these surfaces for their possible application to the miniaturized devices. The tribological evaluation of the DLC nano-dot surfaces was done in comparison with bare Si (1 0 0) surfaces and DLC coated silicon surfaces. A commercial atomic force microscope (AFM) was used to measure adhesion and friction properties of the test materials at the nano-scale, whereas a custom-built micro-tribotester was used to measure their micro-friction property. Results showed that the DLC nano-dot surfaces exhibited superior tribological properties with the lowest values of adhesion force, and friction force both at the nano- and micro-scales, when compared to the bare Si (1 0 0) surfaces and DLC coated silicon surfaces. In addition, the DLC nano-dot surfaces showed no observable wear at the micro-scale, unlike the other two test materials. The superior tribological performance of the DLC nano-dot surfaces is attributed to their hydrophobic nature and the reduced area of contact projected by them. © 2010 Elsevier B.V. All rights reserved. 1. Introduction Over the last decade, the field of MEMS has expanded con- siderably, catering to a wide variety of applications ranging from industrial, consumer, defense, aerospace, to biomedical applica- tions [1]. MEMS devices can be categorized into two main classes, namely: (i) sensors and (ii) actuators. Sensors-based MEMS have only sensing elements, whereas the actuators-based MEMS have elements that undergo relative mechanical motion. Sensors-based MEMS devices are commercially available. However, the actuators- based MEMS have not been commercialized yet, owing to the fact that there exist no robust tribological solutions at micro/nano-scale which can make the devices operate smoothly and reliably. For the smooth functioning of the elements in the actuators-based MEMS, the contact between them must be properly lubricated. But lubrica- tion becomes difficult when the dimensions of machine elements are in micro/nano-scale. At the micro/nano-scale, the surface-area- to-volume ratio is very large. Due to this, the surface forces such as adhesion and friction restrict the smooth operation and reliabil- ity of the actuator-based MEMS. In order to reduce these surface ∗ Corresponding author. Tel.: +82 2 958 5651; fax: +82 2 958 6910. E-mail address: esyoon@kist.re.kr (E.-S. Yoon). forces, solid lubricants (such as graphite or MoS 2 ) cannot be used as they are about the same size as those of the MEMS elements [2]. In addition, conventional liquid lubricants can also be hardly used, as they generate liquid-mediated adhesion [3]. Thus, minimizing the surface forces at small-scales is a real challenge. Miniaturized devices are traditionally made from silicon (Si) due to the well established designing and fabrication processes related to the IC technology. However, Si does not have good tribologi- cal properties [4,5]. In order to improve the tribological properties of Si, researchers world-wide have resorted to a variety of surface modification techniques such as chemical and topographical mod- ifications [5]. Chemical modification includes thin films/coatings such as self-assembled monolayers (SAMs) and DLC coatings [5–8]. Topographical modification includes roughening of surfaces [9] and surface texturing/patterning [10–14]. In this paper, we report a short investigation on the nano- and micro-tribological properties of DLC nano-dot surfaces. The aim of the investigation was to examine the suitability of the surfaces for tribological applications in MEMS devices. 2. Test specimens and experimental details The DLC nano-dot surfaces were created by depositing DLC films on nano-sized nickel (Ni) dots fabricated on Si (1 0 0) wafers by 0169-4332/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.apsusc.2010.10.131