SU8 nanocomposite coatings with improved tribological performance for MEMS (original) (raw)
Related papers
Effect of filler behavior on nanocomposite SU8 photoresist for moving micro-parts
Microelectronic Engineering, 2006
The use of low-stress SU8 nanocomposites as a functional material for micro-parts and coating applications is described in this paper. It was found that the nanoparticles lower the internal stress and decrease the wear rate and frictional coefficient of the SU8 epoxy. The applicability of this technology is demonstrated on gear wheels configuration and coating multilayer capping technology on moving micro-parts.
Tribology - Materials, Surfaces & Interfaces, 2016
SU-8, an epoxy-based negative photoresist polymer, is highly suitable for making micro-electromechanical systems (MEMS) structures. Despite fabrication advantages, its bulk mechanical and tribological properties are the main limitations for application as MEMS material. Carbon filler materials such as graphene, graphite and multi-walled carbon nanotube (MWCNT) are added to SU-8 for tribological and mechanical property enhancements. SU-8/(5 wt%) graphite composite has performed better for the steady-state coefficient of friction at all loads including for the speed effect. SU-8/(5 wt%) MWCNT has shown excellent wear resistance. At 10 wt% graphite content, SU-8/graphite is superior in tribological performance to other composites tested.
Lubrication Mechanism of SU-8/Talc/PFPE Composite
Tribology Letters, 2017
SU-8, a very promising structural polymer for the next-generation 3D fabrication of micro-electromechanical systems (MEMS), has extremely poor tribological properties. The improvement in tribological properties has been recently addressed by developing SU-8/talc (30 wt%) /perfluoropolyether (PFPE) (30 wt%) composite. This composite showed wear durability approximately five orders of magnitude greater in comparison with that of pure SU-8. This drastic increment was found to be because of the in situ lubrication mechanism provided by the PFPE liquid droplets present in the composite. In this present investigation, the lubrication mechanism for SU-8/talc (30 wt%)/PFPE (10, 20 and 30 wt%) composites was further investigated by varying sliding speed (0.1-1.0 m/s) and normal load (2 N and 4 N) using silicon nitride ball of 4 mm diameter as the counterface. The data show that the coefficient of friction and interfacial shear strength follows linear relations with the logarithm of the sliding velocity. Normal load has effect on marginally reducing the coefficient of friction.
An in-situ heating effect study on tribological behavior of SU-8+PFPE composite
Wear, 2013
SU-8 polymer is an emerging structural material for micro-fabrication of MEMS/NEMS devices using photolithography process. However, poor tribological properties of SU-8 restrict its wide applications as a very reliable MEMS material. In our earlier work [1], we have developed SU-8 composites which reduced friction and enhanced wear life of SU-8 by more than four orders of magnitude. The improvements in the properties were attributed to the self-lubricating nature of the composite by continuous supply of the lubricant into the worn areas, the lubricious nature of the filler lubricant perfluoropolyether (PFPE), and possible chemical bonding between SU-8 and PFPE. In this current work, we further investigated the effect of in-situ heating on the tribological performances of the SU-8þ PFPE composite. In-situ heating from room temperature (25 1C) to 100 1C showed a strong effect on the tribological behavior of SU-8þPFPE composite by reducing its initial and steady-state friction coefficients by $ 2 and $ 7 times, respectively. Wear life (n) increased by more than three times due to in-situ heating. Greater surface area coverage by the spreading of PFPE lubricant and migration of PFPE from the bulk to surface are found responsible for this superior tribological performance of the composite at high temperatures.
Tribology Letters, 2011
Tribological properties of optimized SU-8 micro-dot patterns on Silicon (Si) were evaluated using a flat-on-flat tribometer. Sliding tests on the patterns were conducted against a SU-8 spin-coated 2 mm x 2 mm Si substrate at varying normal loads at a fixed rotational speed. It was observed that the pitch of the SU-8 pattern on Si substrate had significant influence on the wear durability. Ultra-thin layer of perfluoropolyether (PFPE) was over-coated onto SU-8 micro-dot patterned specimens for enhanced wear durability, and the specimen of the optimized pitch 450 µm has shown a wear life of more than 100,000 cycles at a normal load of 650 mN.
Different concentrations of graphite powder (particle size < 20 µm) were added for the enhancement in mechanical and tribological properties of SU-8 polymer. The materials were studied as thick coatings with thickness in the range of ~ 35-40 µm on glass substrate. SU-8 and SU-8/graphite composite properties were examined using atomic force microscope (for nanoindentation test) and pin-on-disc tribometer (for friction and wear). The surface characteristics were studied using Optical Microscope, Goniometer and 3D Profilometer. At 10 and 20 wt% graphite concentration, it was found that several properties were enhanced such as elastic modulus ~ 2.2 times, marginal increment in hardness and approximately same water contact angle and same surface free energy (SFE) as compared with those of pure SU-8. More importantly, 10 wt% graphite concentration has given two-times lower steady-state coefficient of friction and ~ 10 times more wear life compared to those of pure SU-8. The 20 wt% composite gave higher coefficient of friction but lower wear rate than the 10 wt% composite.
Surface chemical modification for exceptional wear life of MEMS materials
AIP Advances, 2011
Micro-Electro-Mechanical-Systems (MEMS) are built at micro/nano-scales. At these scales, the interfacial forces are extremely strong. These forces adversely affect the smooth operation and cause wear resulting in the drastic reduction in wear life (useful operating lifetime) of actuator-based devices. In this paper, we present a surface chemical modification method that reduces friction and significantly extends the wear life of the two most popular MEMS structural materials namely, silicon and SU-8 polymer. The method includes surface chemical treatment using ethanolamine-sodium phosphate buffer, followed by coating of perfluoropolyether (PFPE) nanolubricant on (i) silicon coated with SU-8 thin films (500 nm) and (ii) MEMS process treated SU-8 thick films (50 μm). After the surface chemical modification, it was observed that the steady-state coefficient of friction of the materials reduced by 4 to 5 times and simultaneously their wear durability increased by more than three orders ...
Friction and nanowear of hard coatings in reciprocating sliding under milli-newton loads
2005
The wear occurring at very low normal loads and in very small contacts is of prime interest to the field of nanotribology. Friction and wear phenomena in micro-electromechanical components (MEMS) are not well understood and that limits the development of commercial nano components. In this work, wear and friction at loads in the milli-Newton range was investigated under reciprocating sliding where wear and dissipated energy are in the range of nanometers and microjoules, respectively. Reciprocating sliding tests were performed with a modular microtribometer that was operated at normal forces of milli-Newton. This tribometer bridges the gap between macroscale test equipments and the atomic force microscopes. Nanowear tests were carried out for different test durations on hard coatings like DLC and TiN, with silicon nitride balls as the counterbody. After the reciprocating sliding tests at very low loads, the wear tracks were investigated with an atomic force microscope to observe topographical changes in the wear tracks, and to analyze the nanowear. The importance of AFM for characterizing the nanowear appears clearly from this work. The obtained results are compared with existing theories on friction and wear to observe their validity in low load range. The importance of contact pressure and third body interactions in the wear track is also discussed based on AFM observations.
Tribology Online, 2016
Different concentrations of graphite powder (particle size < 20 µm) were added for the enhancement in mechanical and tribological properties of SU-8 polymer. The materials were studied as thick coatings with thickness in the range of ~ 35-40 µm on glass substrate. SU-8 and SU-8/graphite composite properties were examined using atomic force microscope (for nanoindentation test) and pin-on-disc tribometer (for friction and wear). The surface characteristics were studied using Optical Microscope, Goniometer and 3D Profilometer. At 10 and 20 wt% graphite concentration, it was found that several properties were enhanced such as elastic modulus ~ 2.2 times, marginal increment in hardness and approximately same water contact angle and same surface free energy (SFE) as compared with those of pure SU-8. More importantly, 10 wt% graphite concentration has given two-times lower steady-state coefficient of friction and ~ 10 times more wear life compared to those of pure SU-8. The 20 wt% composite gave higher coefficient of friction but lower wear rate than the 10 wt% composite.
Recent Advances in Hard, Tough, and Low Friction Nanocomposite Coatings
Tsinghua Science & Technology, 2005
Nanocomposite coatings demonstrate improved friction and wear responses under severe sliding conditions in extreme environments. This paper provides a review how thin film multilayers and nanocomposites result in hard, tough, low-friction coatings. Approaches to couple multilayered and nanocomposite materials with other surface engineering strategies to achieve higher levels of performance in a variety of tribological applications are also discussed. Encapsulating lubricious phases in hard nanocomposite matrices is one approach that is discussed in detail. Results from state-of-the-art "chameleon" nanocomposites that exhibit reversible adaptability to ambient humidity or temperature are presented.