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Special Issue "15 Years of SU8 as MEMS Material"

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A special issue of Micromachines (ISSN 2072-666X).

Deadline for manuscript submissions: closed (31 March 2015)

Special Issue Editors

Guest Editor
Prof. Dr. Phillipe Renaud (Website)

EPFL-STI-IMT-LMIS, BM-Station 17, CH-1015 Lausanne, Switzerland
Fax: +41 21 693 59 50
Interests: bioMEMS; micro- and nano-fluidics; cell chips; bioelectronics; biosensors
Guest Editor
Dr. Arnaud Bertsch (Website)

EPFL-STI-IMT-LMIS, BM-Station 17, CH-1015 Lausanne, Switzerland
Phone: +41 21 693 66 06
Fax: +41 21 693 59 50
Interests: polymers; MEMS processing; BioMEMS; stereolithography; medical devices

Special Issue Information

Dear Colleagues,

Interest in the use of SU8 as MEMS material was first expressed in 1997; since then SU8 has significantly contributed to the development of a large array of microsystems. First used as a negative photoresist, the high aspect ratio components that were quickly obtained, 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 15 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, molding, etc. 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.

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

We are looking forward to receiving your contributions.

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

Submission

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. Papers will be published continuously (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are refereed through a peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Micromachines is an international peer-reviewed Open Access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 1000 CHF (Swiss Francs).

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
  • Lab on a chip
  • Beyond SU8: alternative high aspect ratio resists

Published Papers (13 papers)

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Editorial

Jump to: Research, Review

Open AccessEditorial Special Issue: 15 Years of SU8 as MEMS Material
Micromachines 2015, 6(6), 790-792; doi:10.3390/mi6060790
Received: 15 June 2015 / Revised: 19 June 2015 / Accepted: 19 June 2015 / Published: 19 June 2015
Cited by 2 | PDF Full-text (624 KB) | HTML Full-text | XML Full-text
Abstract In 1997, the first paper using SU-8 as a material for microfabrication was published [1], demonstrating the interest of this negative photoresist for the near-UV structuration of thick layers and the manufacturing of high aspect-ratio components.[...] Full article
(This article belongs to the Special Issue 15 Years of SU8 as MEMS Material)

Research

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Open AccessArticle Novel SU-8/Ionic Liquid Composite for Tribological Coatings and MEMS
Micromachines 2015, 6(5), 611-621; doi:10.3390/mi6050611
Received: 25 March 2015 / Accepted: 13 May 2015 / Published: 19 May 2015
Cited by 3 | PDF Full-text (5224 KB) | HTML Full-text | XML Full-text
Abstract
Tribology of SU-8 polymer is increasingly relevant due to bursting use of this material in a variety of applications. This study is directed towards introduction and investigation of a novel self-lubricating composite of an ionic liquid (IL) in SU-8. The new material [...] Read more.
Tribology of SU-8 polymer is increasingly relevant due to bursting use of this material in a variety of applications. This study is directed towards introduction and investigation of a novel self-lubricating composite of an ionic liquid (IL) in SU-8. The new material can be utilized for fabrication of lubricating polymer coating with tunable surface properties or SU8-made elements for microelectromechanical systems (MEMS) with enhanced tribological performance. It is shown that addition of IL drastically alters water affinity of the composite while UV patternability remains unmodified. A lower coefficient of friction and wear has been obtained for two investigated compositions with 4 and 10 wt % ionic liquid. Full article
(This article belongs to the Special Issue 15 Years of SU8 as MEMS Material)
Open AccessArticle Transferable Integrated Optical SU8 Devices: From Micronic Waveguides to 1D-Nanostructures
Micromachines 2015, 6(5), 544-553; doi:10.3390/mi6050544
Received: 26 March 2015 / Revised: 20 April 2015 / Accepted: 21 April 2015 / Published: 23 April 2015
Cited by 3 | PDF Full-text (4319 KB) | HTML Full-text | XML Full-text
Abstract
We report on optical components for integrated optics applications at the micro- and nanoscale. Versatile shapes and dimensions are achievable due to the liquid phase processability of SU8 resist. On the one hand, by adjusting the UV-lithography process, waveguiding structures are patterned [...] Read more.
We report on optical components for integrated optics applications at the micro- and nanoscale. Versatile shapes and dimensions are achievable due to the liquid phase processability of SU8 resist. On the one hand, by adjusting the UV-lithography process, waveguiding structures are patterned and released from their original substrate. They can be replaced on any other substrate and also immerged in liquid wherein they still show off efficient light confinement. On the other hand, filled and hollow 1D-nanostructures are achievable by the wetting template method. By exploiting the large range of available SU8 viscosities, nanowires of diameter ranging between 50 nm and 240 nm, as well as nanotubes of controllable wall thickness are presented. Optical injection, propagation, and coupling in such nanostructures are relevant for highly integrated devices. Full article
(This article belongs to the Special Issue 15 Years of SU8 as MEMS Material)
Open AccessArticle Performance of SU-8 Membrane Suitable for Deep X-Ray Grayscale Lithography
Micromachines 2015, 6(2), 252-265; doi:10.3390/mi6020252
Received: 8 December 2014 / Accepted: 4 February 2015 / Published: 9 February 2015
Cited by 4 | PDF Full-text (3745 KB) | HTML Full-text | XML Full-text
Abstract
In combination with tapered-trench-etching of Si and SU-8 photoresist, a grayscale mask for deep X-ray lithography was fabricated and passed a 10-times-exposure test. The performance of the X-ray grayscale mask was evaluated using the TERAS synchrotron radiation facility at the National Institute [...] Read more.
In combination with tapered-trench-etching of Si and SU-8 photoresist, a grayscale mask for deep X-ray lithography was fabricated and passed a 10-times-exposure test. The performance of the X-ray grayscale mask was evaluated using the TERAS synchrotron radiation facility at the National Institute of Advanced Industrial Science and Technology (AIST). Although the SU-8 before photo-curing has been evaluated as a negative-tone photoresist for ultraviolet (UV) and X-ray lithographies, the characteristic of the SU-8 after photo-curing has not been investigated. A polymethyl methacrylate (PMMA) sheet was irradiated by a synchrotron radiation through an X-ray mask, and relationships between the dose energy and exposure depth, and between the dose energy and dimensional transition, were investigated. Using such a technique, the shape of a 26-μm-high Si absorber was transformed into the shape of a PMMA microneedle with a height of 76 μm, and done with a high contrast. Although during the fabrication process of the X-ray mask a 100-μm-pattern-pitch (by design) was enlarged to 120 μm. However, with an increase in an integrated dose energy this number decreased to 99 μm. These results show that the X-ray grayscale mask has many practical applications. In this paper, the author reports on the evaluation results of SU-8 when used as a membrane material for an X-ray mask. Full article
(This article belongs to the Special Issue 15 Years of SU8 as MEMS Material)
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Open AccessArticle Optimized SU-8 Processing for Low-Cost Microstructures Fabrication without Cleanroom Facilities
Micromachines 2014, 5(3), 738-755; doi:10.3390/mi5030738
Received: 14 July 2014 / Revised: 9 September 2014 / Accepted: 12 September 2014 / Published: 22 September 2014
Cited by 14 | PDF Full-text (4715 KB) | HTML Full-text | XML Full-text
Abstract
The study and optimization of epoxy-based negative photoresist (SU-8) microstructures through a low-cost process and without the need for cleanroom facility is presented in this paper. It is demonstrated that the Ultraviolet Rays (UV) exposure equipment, commonly used in the Printed Circuit [...] Read more.
The study and optimization of epoxy-based negative photoresist (SU-8) microstructures through a low-cost process and without the need for cleanroom facility is presented in this paper. It is demonstrated that the Ultraviolet Rays (UV) exposure equipment, commonly used in the Printed Circuit Board (PCB) industry, can replace the more expensive and less available equipment, as the Mask Aligner that has been used in the last 15 years for SU-8 patterning. Moreover, high transparency masks, printed in a photomask, are used, instead of expensive chromium masks. The fabrication of well-defined SU-8 microstructures with aspect ratios more than 20 is successfully demonstrated with those facilities. The viability of using the gray-scale technology in the photomasks for the fabrication of 3D microstructures is also reported. Moreover, SU-8 microstructures for different applications are shown throughout the paper. Full article
(This article belongs to the Special Issue 15 Years of SU8 as MEMS Material)
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Open AccessArticle SU-8 Photolithography as a Toolbox for Carbon MEMS
Micromachines 2014, 5(3), 766-782; doi:10.3390/mi5030766
Received: 26 June 2014 / Revised: 4 September 2014 / Accepted: 9 September 2014 / Published: 22 September 2014
Cited by 4 | PDF Full-text (2053 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
The use of SU-8 as precursor for glass-like carbon, or glassy carbon, is presented here. SU-8 carbonizes when subject to high temperature under inert atmosphere. Although epoxy-based precursors can be patterned in a variety of ways, photolithography is chosen due to its [...] Read more.
The use of SU-8 as precursor for glass-like carbon, or glassy carbon, is presented here. SU-8 carbonizes when subject to high temperature under inert atmosphere. Although epoxy-based precursors can be patterned in a variety of ways, photolithography is chosen due to its resolution and reproducibility. Here, a number of improvements to traditional photolithography are introduced to increase the versatility of the process. The shrinkage of SU-8 during carbonization is then detailed as one of the guidelines necessary to design carbon patterns. A couple of applications—(1) carbon-electrode dielectrophoresis for bioparticle manipulation; and (2) the use of carbon structures as micro-molds are also presented. Full article
(This article belongs to the Special Issue 15 Years of SU8 as MEMS Material)
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Open AccessArticle Inkjet Printing of High Aspect Ratio Superparamagnetic SU-8 Microstructures with Preferential Magnetic Directions
Micromachines 2014, 5(3), 583-593; doi:10.3390/mi5030583
Received: 29 June 2014 / Revised: 2 August 2014 / Accepted: 18 August 2014 / Published: 25 August 2014
Cited by 2 | PDF Full-text (3832 KB) | HTML Full-text | XML Full-text
Abstract
Structuring SU-8 based superparamagnetic polymer composite (SPMPC) containing Fe3O4 nanoparticles by photolithography is limited in thickness due to light absorption by the nanoparticles. Hence, obtaining thicker structures requires alternative processing techniques. This paper presents a method based on inkjet [...] Read more.
Structuring SU-8 based superparamagnetic polymer composite (SPMPC) containing Fe3O4 nanoparticles by photolithography is limited in thickness due to light absorption by the nanoparticles. Hence, obtaining thicker structures requires alternative processing techniques. This paper presents a method based on inkjet printing and thermal curing for the fabrication of much thicker hemispherical microstructures of SPMPC. The microstructures are fabricated by inkjet printing the nanoparticle-doped SU-8 onto flat substrates functionalized to reduce the surface energy and thus the wetting. The thickness and the aspect ratio of the printed structures are further increased by printing the composite onto substrates with confinement pedestals. Fully crosslinked microstructures with a thickness up to 88.8 μm and edge angle of 112° ± 4° are obtained. Manipulation of the microstructures by an external field is enabled by creating lines of densely aggregated nanoparticles inside the composite. To this end, the printed microstructures are placed within an external magnetic field directly before crosslinking inducing the aggregation of dense Fe3O4 nanoparticle lines with in-plane and out-of-plane directions. Full article
(This article belongs to the Special Issue 15 Years of SU8 as MEMS Material)
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Open AccessArticle Implementation of Synchronous Micromotor in Developing Integrated Microfluidic Systems
Micromachines 2014, 5(3), 442-456; doi:10.3390/mi5030442
Received: 5 May 2014 / Revised: 8 June 2014 / Accepted: 7 July 2014 / Published: 18 July 2014
Cited by 9 | PDF Full-text (8098 KB) | HTML Full-text | XML Full-text
Abstract
This paper introduces the synchronous micromotor concept and presents new investigations on its application as an integrated driving mechanism in microfluidic systems. A spiral channel viscous micropump and a microstirrer are considered and tested as examples to verify the concept. The fabrication [...] Read more.
This paper introduces the synchronous micromotor concept and presents new investigations on its application as an integrated driving mechanism in microfluidic systems. A spiral channel viscous micropump and a microstirrer are considered and tested as examples to verify the concept. The fabrication technology of such integrated systems is based on UV depth lithography, electroplating and soft lithography. The synchronous micromotor consists of a stator including double layer coils, and a rotor disk containing alternate permanent magnets. The coils are distributed evenly around the stator and arranged in three phases. The phases are excited by sinusoidal currents with a corresponding phase shift resulting in a rotating magnetic field. Regarding the spiral channel viscous micropump, a spiral disk was fixed onto the rotor disk and run at different rotational speeds. Tests showed very promising results, with a flow rate up to 1023 µL·min−1 at a motor rotational speed of 4500 rpm. Furthermore, for the application of a microstirred-tank bioreactor, the rotor disk design was modified to work as a stirrer. The performance of the developed microbioreactor was tested over a time period of approximately 10 h under constant stirring. Tests demonstrated the successful cultivation of S. cerevisiae through the integration of the microstirrer in a microbioreactor system. These systems prove that synchronous micromotors are well suited to serve as integrated driving mechanisms of active microfluidic components. Full article
(This article belongs to the Special Issue 15 Years of SU8 as MEMS Material)
Open AccessArticle SU-8 Composite Based “Lube-tape” for a Wide Range of Tribological Applications
Micromachines 2014, 5(2), 263-274; doi:10.3390/mi5020263
Received: 21 March 2014 / Revised: 1 May 2014 / Accepted: 8 May 2014 / Published: 19 May 2014
Cited by 1 | PDF Full-text (610 KB) | HTML Full-text | XML Full-text
Abstract
In a previous work, we have developed a perflouropolyether (PFPE) lubricant droplet-filled SU-8 composite which promotes bonding between the molecules of SU-8 and PFPE and provides excellent boundary lubrication. The SU-8 + PFPE composite has enhanced the wear durability of SU-8 by [...] Read more.
In a previous work, we have developed a perflouropolyether (PFPE) lubricant droplet-filled SU-8 composite which promotes bonding between the molecules of SU-8 and PFPE and provides excellent boundary lubrication. The SU-8 + PFPE composite has enhanced the wear durability of SU-8 by more than four orders of magnitude. In this work, the same SU-8 + PFPE composite was used to fabricate a stand-alone laminate film called “Lube-tape”. It has integrated two layers of approximately 90 microns thickness each; the top layer is made of SU-8 + PFPE composite and the bottom layer of pristine SU-8. Thus, a single tape can have drastically contrasting high friction and low friction properties on its two surfaces. The composite side has the initial coefficient of friction ~7 times lower and the wear life more than four orders of magnitude than those of the pristine SU-8 side. This lube tape can be used on any load bearing surface to improve the tribological performance by simply pasting the pristine SU-8 side onto the substrate. Full article
(This article belongs to the Special Issue 15 Years of SU8 as MEMS Material)
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Open AccessArticle Biomimetic Pieris rapae’s Nanostructure and Its Use as a Simple Sucrose Sensor
Micromachines 2014, 5(2), 216-227; doi:10.3390/mi5020216
Received: 25 March 2014 / Revised: 11 April 2014 / Accepted: 14 April 2014 / Published: 23 April 2014
Cited by 1 | PDF Full-text (803 KB) | HTML Full-text | XML Full-text
Abstract
Biomimetics often provides efficient ways to create a product incorporating novel properties. Here we present the replication of the Pieris rapae butterfly optical structure. This butterfly has white wings with black spots. The white coloration is produced by light scattering on pterin [...] Read more.
Biomimetics often provides efficient ways to create a product incorporating novel properties. Here we present the replication of the Pieris rapae butterfly optical structure. This butterfly has white wings with black spots. The white coloration is produced by light scattering on pterin beads ranging from 100 to 500 nm whereas black spots correspond to areas without pterin beads, thus revealing a highly pigmented layer underneath. In order to mimic the butterfly wing structure, we deposited SU-8 beads produced by electrospraying on a black absorbing layer made of black SU-8. We thereby replicated the optical effect observed on Pieris rapae. Additional experiments showed that the white coloration replication is a structural color. Finally, we further demonstrate that these optical engineered surfaces can be used for sucrose sensing in the range of 1 g/L to 250 g/L. Full article
(This article belongs to the Special Issue 15 Years of SU8 as MEMS Material)
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Review

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Open AccessReview Innovative SU-8 Lithography Techniques and Their Applications
Micromachines 2015, 6(1), 1-18; doi:10.3390/mi6010001
Received: 3 October 2014 / Accepted: 9 December 2014 / Published: 23 December 2014
Cited by 4 | PDF Full-text (6689 KB) | HTML Full-text | XML Full-text
Abstract
SU-8 has been widely used in a variety of applications for creating structures in micro-scale as well as sub-micron scales for more than 15 years. One of the most common structures made of SU-8 is tall (up to millimeters) high-aspect-ratio (up to [...] Read more.
SU-8 has been widely used in a variety of applications for creating structures in micro-scale as well as sub-micron scales for more than 15 years. One of the most common structures made of SU-8 is tall (up to millimeters) high-aspect-ratio (up to 100:1) 3D microstructure, which is far better than that made of any other photoresists. There has been a great deal of efforts in developing innovative unconventional lithography techniques to fully utilize the thick high aspect ratio nature of the SU-8 photoresist. Those unconventional lithography techniques include inclined ultraviolet (UV) exposure, back-side UV exposure, drawing lithography, and moving-mask UV lithography. In addition, since SU-8 is a negative-tone photoresist, it has been a popular choice of material for multiple-photon interference lithography for the periodic structure in scales down to deep sub-microns such as photonic crystals. These innovative lithography techniques for SU-8 have led to a lot of unprecedented capabilities for creating unique micro- and nano-structures. This paper reviews such innovative lithography techniques developed in the past 15 years or so. Full article
(This article belongs to the Special Issue 15 Years of SU8 as MEMS Material)
Open AccessReview SU-8 as a Material for Microfabricated Particle Physics Detectors
Micromachines 2014, 5(3), 594-606; doi:10.3390/mi5030594
Received: 17 June 2014 / Revised: 1 August 2014 / Accepted: 4 August 2014 / Published: 26 August 2014
Cited by 1 | PDF Full-text (2132 KB) | HTML Full-text | XML Full-text
Abstract
Several recent detector technologies developed for particle physics applications are based on microfabricated structures. Detectors built with this approach generally exhibit the overall best performance in terms of spatial and time resolution. Many properties of the SU-8 photoepoxy make it suitable for [...] Read more.
Several recent detector technologies developed for particle physics applications are based on microfabricated structures. Detectors built with this approach generally exhibit the overall best performance in terms of spatial and time resolution. Many properties of the SU-8 photoepoxy make it suitable for the manufacturing of microstructured particle detectors. This article aims to review some emerging detector technologies making use of SU-8 microstructuring, namely micropattern gaseous detectors and microfluidic scintillation detectors. The general working principle and main process steps for the fabrication of each device are reported, with a focus on the advantages brought to the device functionality by the use of SU-8. A novel process based on multiple bonding steps for the fabrication of thin multilayer microfluidic scintillation detectors developed by the authors is presented. Finally, a brief overview of the applications for the discussed devices is given. Full article
(This article belongs to the Special Issue 15 Years of SU8 as MEMS Material)
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Open AccessReview UV-LIGA: From Development to Commercialization
Micromachines 2014, 5(3), 486-495; doi:10.3390/mi5030486
Received: 17 June 2014 / Revised: 14 July 2014 / Accepted: 15 July 2014 / Published: 23 July 2014
Cited by 4 | PDF Full-text (10144 KB) | HTML Full-text | XML Full-text
Abstract
A major breakthrough in UV-LIGA (Lithographie, Galvanoformung and Abformung) started with the use of epoxy-based EPON® SU-8 photoresist in the mid-1990s. Using this photoresist has enabled the fabrication of tall and high aspect ratio structures without the use of a very [...] Read more.
A major breakthrough in UV-LIGA (Lithographie, Galvanoformung and Abformung) started with the use of epoxy-based EPON® SU-8 photoresist in the mid-1990s. Using this photoresist has enabled the fabrication of tall and high aspect ratio structures without the use of a very expensive synchrotron source needed to expose the photoresist layer in X-ray LIGA. SU-8 photoresist appeared to be well-suited for LIGA templates, but also as a permanent material. Based on UV-LIGA and SU-8, Mimotec SA has developed processes to manufacture mold inserts and metallic components for various market fields. From one to three-level parts, from Ni to other materials, from simple to complicated parts with integrated functionalities, UV-LIGA has established itself as a manufacturing technology of importance for prototyping, as well as for mass-fabrication. This paper reviews some of the developments that led to commercial success in this field. Full article
(This article belongs to the Special Issue 15 Years of SU8 as MEMS Material)

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