20 Years of SU8 as MEMS Material

A special issue of Micromachines (ISSN 2072-666X). This special issue belongs to the section "D:Materials and Processing".

Deadline for manuscript submissions: closed (31 May 2021) | Viewed by 22358

Special Issue Editors


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Guest Editor
EPFL-STI-IMT-LMIS, BM-Station 17, CH-1015 Lausanne, Switzerland
Interests: polymers; MEMS processing; BioMEMS; stereolithography; medical devices
Special Issues, Collections and Topics in MDPI journals

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Guest Editor
EPFL-STI-IMT-LMIS, BM-Station 17, CH-1015 Lausanne, Switzerland
Interests: bioMEMS; micro- and nano-fluidics; cell chips; bioelectronics; biosensors
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Since its first use as MEMs material in 1997, SU8 has significantly contributed to the development of a large array of microsystems. First used as a negative photoresist, the quickly obtained high aspect ratio components and the possibility to easily pattern multilevel structures made it a polymer of choice for the UV-LIGA process and led to its early adoption in industrial applications. In the last 20 years, SU8 has been largely used in academic research for a large range of applications: structural components, optical waveguides, micro-channels for microfluidic and lab-on-chip applications, micro-mixers, cell-chips, bio-related applications, etc. In addition to UV-photolithography, many other micro-patterning methods have been used to process SU8, such as electron-beam lithography, laser ablation, thermal and UV nano-imprinting, inkjet printing, and molding. Composite materials based on SU8 have also been developed by the addition of a wide variety of fillers, such as nanoparticles, carbon nanotubes, carbon black, ceramic powders, and many others. In recent years, the interest in SU8 in the MEMS community has continued to grow and has led to a number of new applications, some of them using SU8 in very innovative and unexpected ways.

This Special Issue aims to highlight the current state of the art in the use of SU8 for micro- or nanotechnology. We invite contributions on all aspects related to SU8, including its processing techniques, its use in new composite resists, its academic and industrial developments, and its use for manufacturing systems in optics, biology, medicine, chemistry, mechanics, fluidics, etc.

We are looking forward to receiving your contributions.

Prof. Arnaud Bertsch
Prof. Dr. Phillipe Renaud
Guest Editors

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Keywords

  • SU8
  • UV-LIGA
  • nanopatterning
  • SU8-based composite materials
  • new processing techniques for SU8
  • SU8 as structural material
  • etching SU8
  • innovative micro-components
  • cell-chips
  • medical devices
  • SU8-based waveguides
  • application of SU8 in optics
  • characterization of SU8 and SU8-based composites
  • PDMS devices made from SU8 molding
  • microfluidics
  • lab on a chip
  • beyond SU8: alternative high aspect ratio resists

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Published Papers (5 papers)

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Research

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14 pages, 5878 KiB  
Article
Integration of Ultra-Low Volume Pneumatic Microfluidics with a Three-Dimensional Electrode Network for On-Chip Biochemical Sensing
by Saurabh Tomar, Charlotte Lasne, Sylvain Barraud, Thomas Ernst and Carlotta Guiducci
Micromachines 2021, 12(7), 762; https://doi.org/10.3390/mi12070762 - 28 Jun 2021
Cited by 2 | Viewed by 3877
Abstract
This paper reports a novel miniaturized pseudo reference electrode (RE) design for biasing Ion Sensitive Field Effect Transistors (ISFETs). It eliminates the need for post-CMOS processing and can scale up in numbers with the CMOS scaling. The presented design employs silane-mediated transfer of [...] Read more.
This paper reports a novel miniaturized pseudo reference electrode (RE) design for biasing Ion Sensitive Field Effect Transistors (ISFETs). It eliminates the need for post-CMOS processing and can scale up in numbers with the CMOS scaling. The presented design employs silane-mediated transfer of patterned gold electrode lines onto PDMS microfluidics such that the gold conformally coats the inside of microfluidic channel. Access to this electrode network is made possible by using “through-PDMS-vias” (TPV), which consist of high metal-coated SU-8 pillars manufactured by a novel process that employs a patterned positive resist layer as SU-8 adhesion depressor. When integrated with pneumatic valves, TPV and pseudo-RE network were able to bias 1.5 nanoliters (nL) of isolated electrolyte volumes. We present a detailed characterization of our pseudo-RE design demonstrating ISFET operation and its DC characterization. The stability of pseudo-RE is investigated by measuring open circuit potential (OCP) against a commercial Ag/AgCl reference electrode. Full article
(This article belongs to the Special Issue 20 Years of SU8 as MEMS Material)
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13 pages, 3094 KiB  
Article
Dry Film Resist Laminated Microfluidic System for Electrical Impedance Measurements
by Yuan Cao, Julia Floehr, Sven Ingebrandt and Uwe Schnakenberg
Micromachines 2021, 12(6), 632; https://doi.org/10.3390/mi12060632 - 29 May 2021
Cited by 15 | Viewed by 3826
Abstract
In micro-electrical-mechanical systems (MEMS), thick structures with high aspect ratios are often required. Dry film photoresist (DFR) in various thicknesses can be easily laminated and patterned using standard UV lithography. Here, we present a three-level DFR lamination process of SUEX for a microfluidic [...] Read more.
In micro-electrical-mechanical systems (MEMS), thick structures with high aspect ratios are often required. Dry film photoresist (DFR) in various thicknesses can be easily laminated and patterned using standard UV lithography. Here, we present a three-level DFR lamination process of SUEX for a microfluidic chip with embedded, vertically arranged microelectrodes for electrical impedance measurements. To trap and fix the object under test to the electrodes, an aperture is formed in the center of the ring-shaped electrodes in combination with a microfluidic suction channel underneath. In a proof-of-concept, the setup is characterized by electrical impedance measurements with polystyrene and ZrO2 spheres. The electrical impedance is most sensitive at approximately 2 kHz, and its magnitudes reveal around 200% higher values when a sphere is trapped. The magnitude values depend on the sizes of the spheres. Electrical equivalent circuits are applied to simulate the experimental results with a close match. Full article
(This article belongs to the Special Issue 20 Years of SU8 as MEMS Material)
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19 pages, 5793 KiB  
Article
Selective Direct Laser Writing of Pyrolytic Carbon Microelectrodes in Absorber-Modified SU-8
by Emil Ludvigsen, Nina Ritter Pedersen, Xiaolong Zhu, Rodolphe Marie, David M. A. Mackenzie, Jenny Emnéus, Dirch Hjorth Petersen, Anders Kristensen and Stephan Sylvest Keller
Micromachines 2021, 12(5), 564; https://doi.org/10.3390/mi12050564 - 17 May 2021
Cited by 7 | Viewed by 2808
Abstract
Pyrolytic carbon microelectrodes (PCMEs) are a promising alternative to their conventional metallic counterparts for various applications. Thus, methods for the simple and inexpensive patterning of PCMEs are highly sought after. Here, we demonstrate the fabrication of PCMEs through the selective pyrolysis of SU-8 [...] Read more.
Pyrolytic carbon microelectrodes (PCMEs) are a promising alternative to their conventional metallic counterparts for various applications. Thus, methods for the simple and inexpensive patterning of PCMEs are highly sought after. Here, we demonstrate the fabrication of PCMEs through the selective pyrolysis of SU-8 photoresist by irradiation with a low-power, 806 nm, continuous wave, semiconductor-diode laser. The SU-8 was modified by adding Pro-Jet 800NP (FujiFilm) in order to ensure absorbance in the 800 nm range. The SU-8 precursor with absorber was successfully converted into pyrolytic carbon upon laser irradiation, which was not possible without an absorber. We demonstrated that the local laser pyrolysis (LLP) process in an inert nitrogen atmosphere with higher laser power and lower scan speed resulted in higher electrical conductance. The maximum conductivity achieved for a laser-pyrolyzed line was 14.2 ± 3.3 S/cm, with a line width and thickness of 28.3 ± 2.9 µm and 6.0 ± 1.0 µm, respectively, while the narrowest conductive line was just 13.5 ± 0.4 µm wide and 4.9 ± 0.5 µm thick. The LLP process seemed to be self-limiting, as multiple repetitive laser scans did not alter the properties of the carbonized lines. The direct laser writing of adjacent lines with an insulating gap down to ≤5 µm was achieved. Finally, multiple lines were seamlessly joined and intersected, enabling the writing of more complex designs with branching electrodes and the porosity of the carbon lines could be controlled by the scan speed. Full article
(This article belongs to the Special Issue 20 Years of SU8 as MEMS Material)
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Review

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19 pages, 5184 KiB  
Review
Biocompatibility of SU-8 and Its Biomedical Device Applications
by Ziyu Chen and Jeong-Bong Lee
Micromachines 2021, 12(7), 794; https://doi.org/10.3390/mi12070794 - 4 Jul 2021
Cited by 33 | Viewed by 4775
Abstract
SU-8 is an epoxy-based, negative-tone photoresist that has been extensively utilized to fabricate myriads of devices including biomedical devices in the recent years. This paper first reviews the biocompatibility of SU-8 for in vitro and in vivo applications. Surface modification techniques as well [...] Read more.
SU-8 is an epoxy-based, negative-tone photoresist that has been extensively utilized to fabricate myriads of devices including biomedical devices in the recent years. This paper first reviews the biocompatibility of SU-8 for in vitro and in vivo applications. Surface modification techniques as well as various biomedical applications based on SU-8 are also discussed. Although SU-8 might not be completely biocompatible, existing surface modification techniques, such as O2 plasma treatment or grafting of biocompatible polymers, might be sufficient to minimize biofouling caused by SU-8. As a result, a great deal of effort has been directed to the development of SU-8-based functional devices for biomedical applications. This review includes biomedical applications such as platforms for cell culture and cell encapsulation, immunosensing, neural probes, and implantable pressure sensors. Proper treatments of SU-8 and slight modification of surfaces have enabled the SU-8 as one of the unique choices of materials in the fabrication of biomedical devices. Due to the versatility of SU-8 and comparative advantages in terms of improved Young’s modulus and yield strength, we believe that SU-8-based biomedical devices would gain wider proliferation among the biomedical community in the future. Full article
(This article belongs to the Special Issue 20 Years of SU8 as MEMS Material)
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24 pages, 6889 KiB  
Review
Fabrication of Functional Microdevices in SU-8 by Multi-Photon Lithography
by Pooria Golvari and Stephen M. Kuebler
Micromachines 2021, 12(5), 472; https://doi.org/10.3390/mi12050472 - 21 Apr 2021
Cited by 22 | Viewed by 4864
Abstract
This review surveys advances in the fabrication of functional microdevices by multi-photon lithography (MPL) using the SU-8 material system. Microdevices created by MPL in SU-8 have been key to progress in the fields of micro-fluidics, micro-electromechanical systems (MEMS), micro-robotics, and photonics. The review [...] Read more.
This review surveys advances in the fabrication of functional microdevices by multi-photon lithography (MPL) using the SU-8 material system. Microdevices created by MPL in SU-8 have been key to progress in the fields of micro-fluidics, micro-electromechanical systems (MEMS), micro-robotics, and photonics. The review discusses components, properties, and processing of SU-8 within the context of MPL. Emphasis is focused on advances within the last five years, but the discussion also includes relevant developments outside this period in MPL and the processing of SU-8. Novel methods for improving resolution of MPL using SU-8 and discussed, along with methods for functionalizing structures after fabrication. Full article
(This article belongs to the Special Issue 20 Years of SU8 as MEMS Material)
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