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Lithography
Published in Andrew Sarangan, Nanofabrication, 2016
SU-8 is a negative-tone chemically amplified photoresist, developed by IBM, that cross-links and hardens when exposed to UV light followed by a heating step [59]. It is based on a chemical known as EPON resin SU-8. It is combined with a photoacid generator and is dissolved in an organic solvent such as cyclopentanone [60–62]. The quantity of the solvent determines the viscosity of the film and hence the thickness of the spin-coated film. Upon exposure to UV light, the photoacid generator produces an acid in the exposed areas of the film. During the heating step, this acid acts as a catalyst for the cross-linking reaction of the resin. The heating step also regenerates more acid in those areas through a chemical amplification process, resulting in a significantly higher sensitivity.
SU-8 Photolithography and Its Impact on Microfluidics
Published in Sushanta K. Mitra, Suman Chakraborty, Fabrication, Implementation, and Applications, 2016
Rodrigo Martinez-Duarte, Marc J. Madou
The versatility of SU-8 has positioned it as one of the most important materials in polymer microfabrication. Microfluidics benefits from SU-8 photolithography in the batch fabrication of structures of high aspect ratio and/or large surface area, which can range in size from a few millimeters down to tens of nanometers. The good mechanical and excellent chemical properties of cross-linked SU-8 yield polymer microfluidics devices that can handle a variety of samples such as blood, urine, milk, and so forth, as well as buffers and cleaning agents at a wide range of flow pressures and working temperatures. SU-8 has a high transparency for light at wavelengths more than 400 nm and allows for the use of fluorescence and other visualization and detection techniques that are common in microfluidics. The recent commercial introduction of SU-8 with dyes and nanoparticles incorporated in it further enlarges the potential of this photoresist in microfluidics and other applications. SU-8 photolithography yields or supports the fabrication of research devices that are applied in a variety of fields including optics, precision mechanics, energy, and space. Furthermore, complex carbon microstructures can be derived by pyrolyzing SU-8 patterns, a technique known as carbon MEMS (Wang et al., 2005).
Polymer Technologies
Published in Ghenadii Korotcenkov, Handbook of Humidity Measurement, 2020
As is seen in Table 19.8, SU-8, polyimide, and Parylene really have great potential for making various MEMS elements. However, the polymer most commonly used for manufacturing microcantilevers and membranes, acceptable for the use of humidity sensors, is SU-8 (Jiguet et al. 2004; Johansson et al. 2005; Lukes and Dickensheets 2013). SU-8, a photopolymerizable epoxy-acrylate polymer (glycidyl-ether-bisphenol-A novolac), is a negative photosensitive polymer used as a structuring material in MEMS and for fabrication purposes within the micro-total-analysis-system (lTAS) area (Carlier et al. 2004). SU-8 is highly transparent in the UV region, allowing fabrication of relatively thick (hundreds of micrometers) structures with nearly vertical side walls. The SU-8 photoresist is most commonly exposed with conventional UV (350–400 nm) radiation, although i-line (365 nm) is the recommended wavelength. SU-8 may also be exposed with e-beam or X-ray radiation. As it can be seen from its formula, the SU-8 polymer has quite low molecular weight (~7000) and thus, when non-cross-linked can easily be dissolved by a number of solvents (e.g., propylene-glycol-methyl ether, gamma-butyrol-acetone, and methyl iso-butyl ketone). Typically, the lithography of SU-8 involves a set of processing steps similar to standard thick photoresists (Kim and Meng 2016): (1) deposition on a substrate (usually via spinning); (2) a softbake to evaporate the solvent; (3) exposure to cross-link the polymer: the exposure of this polymer to UV light generates a strong photoacid, which protonates the epoxy groups of the monomer and starts a cross-linking reaction to create a highly cross-linked polymer (Martinez-Duarte 2014); (4) post-exposure bake to finalize the cross-linking; and (5) development to reveal the cross-linked structure. After exposition and developing, its highly cross-linked structure gives it high stability to chemicals and radiation damage. Cured cross-linked SU-8 shows very low levels of outgassing. The last one is good for gas and humidity-sensor design. Parameters of SU-8 are listed in Table 19.11.
Controlled formation of topological defects of liquid crystals in micro-wells
Published in Liquid Crystals, 2022
Haruka Sakanoue, Saki Yamashita, Tomoki Murakami, Hiroaki Suzuki, Kenji Katayama
Micro-wells were fabricated by pouring PDMS into a master mould using standard soft lithography. The master mould was fabricated by photolithography. A negative photoresist SU-8 3005 (Nippon Kayaku) was spin-coated on a 2-inch silicon wafer for making the SU-8 layer with thicknesses of 5, 6, 10, or 20 μm. After making a patterned mask designed using CAD software (Rhinoceros 6.0), the pattern was transferred onto the SU-8 on a wafer by UV light irradiation through the mask. An unnecessary resist was developed, and an anti-adhesion layer was added with a fluorine coating agent (FG-5084SH-0.1, FLUORO TECHNOLOGY) to facilitate the release of PDMS. PDMS resin (SYLGARDTM 184 Silicone Elastomer, DOW) mixed with a curing agent at the weight ratio of 10:1 was poured onto the master mould and degassed in a desiccator to remove the air bubbles. The PDMS was cured by baking at 80°C for 2 hours and was peeled from the mould.
Magneto-ionic suppression of magnetic vortices
Published in Science and Technology of Advanced Materials, 2021
Yu Chen, Aliona Nicolenco, Pau Molet, Agustin Mihi, Eva Pellicer, Jordi Sort
Magnetic nanopillars comprising electrodeposited Co and sputtered GdOx layers were prepared onto metallized Si substrates covered with a nanoimprinted resist, as schematically illustrated in Figure 1(a). Figure 1(b) shows a representative top-view SEM micrograph of the as-deposited Co pillars inside the template. The diameter of the pillars is given by the size of the pores and is around 200 nm. The pillars exhibit some roughness (Figure 1(c)) provided by the polycrystalline grain growth during electrodeposition. It is worth mentioning that the polymeric template was not removed at any stage of the experiment. The SU-8 polymer (epoxy-based, negative tone resist) is commonly used in various micro-/nanoelectromechanical systems (MEMS/NEMS) due to its outstanding chemical and thermal resistivity, optical transparency and easy fabrication of high-aspect-ratio features. In addition, it is an electrical insulator (breakdown field ~108 V m−1). Thanks to such properties, SU-8 is an ideal material to be fully integrated in electronics, functional MEMS/NEMS devices and lab-on-chip microsystems [75]. Since the Co pillars do not completely fill the pores of the template, sputtering GdOx on top of such structures renders an array of bilayered nanopillars with a Co/GdOx interface roughly parallel to the substrate.
Tribological analysis of tip-cantilever made of SU-8, talc and PFPE composite
Published in Tribology - Materials, Surfaces & Interfaces, 2020
Jitendra K. Katiyar, Sujeet K. Sinha, Tomoko Hirayama, Arvind Kumar
Pure SU-8 has shown potential in its application in microsystems such as MEMS. However, its composites have not been studied so extensively. Pure SU-8 micro-structures (such as cantilever) were fabricated and tested for their bulk mechanical properties [25]. Jaguet et al. [7] have fabricated SU-8/SiO2 based nanocomposite coatings and found that inclusion of filler reduced the internal interfacial stress, however, the CoF was still high when rubbed against a steel ball, though it reduced drastically when polyoxymethylene (POM) ball was used as the counterface. It is apparent that SU-8 based composites provide huge potential for application as micro-components for MEMS, an area which has not been pursued so far. In our previous work, we have found that talc has profound influence on improving the mechanical properties of SU-8, and in-situ lubrication of SU-8 by liquid perfluoropolyether (PFPE) reduces the CoF [15]. However, this composite has not been tested yet at component level to understand the effects of fabrication process parameters on the bulk and surface properties. SU-8 with 30 wt-% talc and 30 wt-% PFPE composite was optimized for mechanical and tribological properties in our previous work [16]. Therefore, it is important to test this composite composition in a microsystem device. With this aim, a conical tip was fabricated on a cantilever made of the SU-8 composite material. The tip was slid over a pure SU-8 surface in linear reciprocation under light normal load. The corresponding CoF was measured using a load cell and the wear rate was calculated from the weight loss of the composite tip.