SU‐8 as a structural material for labs‐on‐chips and microelectromechanical systems

Abstract

Since its introduction in the nineties, the negative resist SU-8 has been increasingly used in micro- and nanotechnologies. SU-8 has made the fabrication of high-aspect ratio structures accessible to labs with no high-end facilities such as X-ray lithography systems or deep reactive ion etching systems. These low-cost techniques have been applied not only in the fabrication of metallic parts or molds, but also in numerous other micromachining processes. Its ease of use has made SU-8 to be used in many applications, even when high-aspect ratios are not required. Beyond these pattern transfer applications, SU-8 has been used directly as a structural material for microelectromechanical systems and microfluidics due to its properties such as its excellent chemical resistance or the low Young modulus. In contrast to conventional resists, which are used temporally, SU-8 has been used as a permanent building material to fabricate microcomponents such as cantilevers, membranes, and microchannels. SU-8-based techniques have led to new low-temperature processes suitable for the fabrication of a wide range of objects, from the single component to the complete lab-on-chip. First, this article aims to review the different techniques and provides guidelines to the use of SU-8 as a structural material. Second, practical examples from our respective labs are presented.

SU-8 Photolithography as a Toolbox for Carbon MEMS

“…The contrary is recommended when features with a wide footprint are desired, since increased baking times or temperatures can introduce stress in the matrix and lead to cracking and feature lift-off during development. The basics of SU-8 photolithography have been previously covered by a number of authors [25,26], including the current one [27], and are out of the scope of this work. Instead, here, I briefly present a number of possible improvements in different stages of the photolithography process to increase its versatility.…”

Enhancement of Electrical and Mechanical Properties of SU-8 Photocrosslinked Coatings Containing Polypyrrole-graphene Oxide Nanoparticles

“…A soft-bake at 80ºC was performed for 10 min in order to promote the solvent evaporation. Photo-curing of the formulations was obtained using Fusion lamp (H bulb, light intensity on the surface of the sample 150 mW/cm 2 , measured with EIT instrument), and a tack-free and free-standing films (thickness 50 µm) were obtained after three passages under the light (velocity of the belt 6 m/min) and they were fully characterized after a post-exposure bake at 80ºC for 1 h.…”

“…Photolithography has traditionally been used to transfer a pattern in a thin film for the preparation of photoresists, but recently it is also used as structural material in micro-and nanotechnologies [2]. In this technology, SU-8 epoxy based negative tone photoresist is extensively employed because of its good thermo-mechanical properties [3].…”

SU-8 Composite Based “Lube-tape” for a Wide Range of Tribological Applications

“…Each SU-8 molecule consists of an average of 8 epoxy groups (and hence the name SU-8). SU-8 is finding many applications in micromachines [2] and bio-MEMS as a structural material because of its UV-curing property, however, it suffers from the major drawbacks of high friction and low wear life. Hence, it cannot be used in a tribological application where the coefficient of friction is to be low and wear life to be high, unless SU-8 is modified suitably.…”

“…The significant improvement in tribological properties of SU-8 by the addition of PFPE can be attributed to the possible ether bond formation between the SU-8 and PFPE molecules [11,12]. The possible etherification reaction is depicted in Equation (2). It is postulated that the -OH terminal groups in the PFPE polymer and the carbocations (C + ) in the SU-8 polymer (epoxide ring) undergo the reaction, which breaks the existing bond and forms new linkage through ether bonds.…”