Literature on polymer fabrication

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  • ma-N 400 and ma-N 1400 - Negative Tone Photoresists, Micro Resist Technology GmbH (2008)
    Titlema-N 400 and ma-N 1400 - Negative Tone Photoresists
    AuthorMicro Resist Technology GmbH
  • Shrinkage ratio of PDMS and its alignment method for the wafer level process, Seok Lee et al. (2008)
    TitleShrinkage ratio of PDMS and its alignment method for the wafer level process
    AuthorsSeok Lee, Seung Lee
    PublicationMicrosystem Technologies
    DateFebruary 05, 2008
    AbstractIn the research area known as Lab-on-a-Chip, poly-dimethylsiloane (PDMS) is a popular material whose fabrication method is the replication of patterns by curing on a mold. Shrinkage of PDMS occurs when it is cured; this is a problem related to the alignment between the PDMS layer and the rigid substrate during the wafer-level processing. In this paper, the 2D shrinkage ratio of PDMS is measured experimentally for various curing conditions including the temperature, thickness, and mixing ratio of the curing agent and dilutant. In order to measure this, scale marks were patterned onto a 4 in. wafer and replicated onto a PDMS substrate. When the patterned Si wafer and PDMS substrate were aligned, the difference of each scale mark was observed. A cross-shaped groove was patterned with a scale mark as a align key for the easy alignment of substrates. For a general recipe, the measured shrinkage ratios of PDMS were 1.06, 1.52 and 1.94% for curing temperature of 65, 80 and 100�C, respectively. Considering the shrinkage ratio of PDMS, the design offset applied in a photomask is 1.07, 1.54 and 1.98% for curing temperature of 65, 80 and 100�C, respectively.
  • Fabrication of complex multilevel microchannels in PDMS by using three-dimensional photoresist masters, Kwang-Seok Yun et al. (2008)
    TitleFabrication of complex multilevel microchannels in PDMS by using three-dimensional photoresist masters
    AuthorsKwang-Seok Yun, Euisik Yoon
    PublicationLab on a Chip
    AbstractThis paper demonstrates a new method of implementing complex microchannels in PDMS, which is simply constructed using three-dimensional photoresist structures as a master mold for the PDMS replica process. The process utilizes UV-insensitive LOR resist as a sacrificial layer to levitate the structural photoresist. In addition, the thickness of photoresist structures can be controlled by multi-step UV exposure. By using these techniques, various three-dimensional photoresist structures were successfully implemented, including the recessed cantilevers, suspended bridges, and the complex plates with micro-pits or micro-villi. We demonstrate that the three-dimensional photoresist structures are applicable to implementing complex multiple microchannels in PDMS by using the PDMS replica method.
  • Polymethylhydrosiloxane (PMHS) as a functional material for microfluidic chips, S. J. Lee et al. (2008)
    TitlePolymethylhydrosiloxane (PMHS) as a functional material for microfluidic chips
    AuthorsS. J. Lee, M. Goedert, M. T. Matyska, E. M. Ghandehari, M. Vijay, J. J. Pesek
    PublicationJournal of Micromechanics and Microengineering
    AbstractPolymethylhydrosiloxane (PMHS) has been investigated as a candidate material for microfluidic chips. The ability to modify the surface of PMHS by hydrosilation is particularly advantageous for separation processes. The chemical modification of PMHS is verified by diffuse reflectance infrared Fourier transform (DRIFT) analysis, and the modified PMHS is shown to be stable when exposed to extreme pH conditions between 2 and 9. Spectrophotometer measurements show that PMHS exhibits over 40% transmittance for ultraviolet (UV) wavelength as low as 220 nm, indicating viability for sensor applications based on UV absorption. The UV transmittance is furthermore observed to be insensitive to thickness for specimens tested between 1.6 mm and 6.4 mm thick. Full curing of PMHS liquid resin occurs between 48 and 72 h at 110 °C with no secondary additives. Casting of microscale features is achieved by using soft lithography methods similar to established techniques for fabrication based on polydimethylsiloxane (PDMS). Microchannels approximately 100 µm wide and 50 µm deep are also demonstrated by carbon dioxide laser ablation, with uniform channels produced using an energy dose of 0.2 mJ mm[?]1 with respect to line length. Other basic functional requirements for microfluidic chips are discussed, including the ability to bond PMHS substrates by plasma treatment.
  • A three-dimensional microfabrication system for biodegradable polymers with high resolution and biocompatibility, Akira Yamada et al. (2008)
    TitleA three-dimensional microfabrication system for biodegradable polymers with high resolution and biocompatibility
    AuthorsAkira Yamada, Fuminori Niikura, Koji Ikuta
    PublicationJournal of Micromechanics and Microengineering
    AbstractBiodegradable polylactide polymers are already widely used in medicine. While further applications are eagerly awaited, progress has been impeded by a lack of appropriate processing methods. Our group attempted to construct a novel three-dimensional microfabrication system for the free processing of three-dimensional micro-level forms. The system processed the polymers with extremely high precision using a fine nozzle. An evaluation of one of the piled-up layers of the extruded lines revealed lateral and depth resolutions of 40 µm and 45 µm, respectively. Micro-pipes, micro-bends and micro-coil springs were fabricated in less than 15 min by stacking up melted polymers from a nozzle. A batch process was adopted for the supply of the materials in order to eliminate the use of toxic solvents, one of the necessary evils with earlier fabrication techniques. Microstructures fabricated by our system and by a conventional method were tested in tensile strength tests to compare the mechanical strengths. The biocompatibility of a newly fabricated structure was tested by cultivating a cell line (PC12) in a small poly(lactic acid) (PLA) vessel with a transparent base, then comparing the morphology and growth with those of the same PC12 line cultivated by a standard vessel.
  • Large-area, high-aspect-ratio SU-8 molds for the fabrication of PDMS microfluidic devices, S. Natarajan et al. (2008)
    TitleLarge-area, high-aspect-ratio SU-8 molds for the fabrication of PDMS microfluidic devices
    AuthorsS. Natarajan, D. A. Chang-Yen, B. K. Gale
    PublicationJournal of Micromechanics and Microengineering
    AbstractA relatively low-cost fabrication method using soft lithography and molding for large-area, high-aspect-ratio microfluidic devices, which have traditionally been difficult to fabricate, has been developed and is presented in this work. The fabrication process includes novel but simple modifications of conventional microfabrication steps and can be performed in any standard microfabrication facility. Specifically, the fabrication and testing of a microfluidic device for continuous flow deposition of bio-molecules in an array format are presented. The array layout requires high-aspect-ratio elastomeric channels that are 350 µm tall, extend more than 10 cm across the substrate and are separated by as little as 20 µm. The mold from which these channels were fabricated consisted of high-quality, 335 µm tall SU-8 structures with a high-negative aspect ratio of 17 on a 150 mm silicon wafer and was produced using spin coating and UV-lithography. Several unique processing steps are introduced into the lithographic patterning to eliminate many of the problems experienced when fabricating tall, high-aspect-ratio SU-8 structures. In particular, techniques are used to ensure uniform molds, both in height and quality, that are fully developed even in the deep negative-aspect-ratio areas, have no leftover films at the top of the structures caused by overexposure and no bowing or angled sidewalls from diffraction of the applied UV light. Successful microfluidic device creation was demonstrated using these molds by casting, curing and bonding a polydimethylsiloxane (PDMS) elastomer. A unique microfluidic device, requiring these stringent geometries, for continuous flow printing of a linear array of 16 protein and antibody spots has been demonstrated and validated by using surface plasmon resonance imaging of printed arrays.
  • Fabrication of high-aspect-ratio nano structures using a nano x-ray shadow mask, Yong Chul Kim et al. (2008)
    TitleFabrication of high-aspect-ratio nano structures using a nano x-ray shadow mask
    AuthorsYong Chul Kim, Seung S. Lee
    PublicationJournal of Micromechanics and Microengineering
    AbstractThis paper describes a novel method for the fabrication of high-aspect-ratio nano structures (HAR-nano structures) using a nano x-ray shadow mask and deep x-ray lithography (DXRL). The nano x-ray shadow mask is fabricated by depositing an x-ray absorber layer (Au, 3 µm) onto the back side of a nano shadow mask. The nano shadow mask is produced with nano-sized apertures whose dimensions are reduced to several tens of nanometers by the accumulation of low-stress silicon nitride (SixNy) using the LPCVD process on the shadow mask. A shadow mask containing apertures with a size of 1 µm is fabricated on a bulk micromachined SixNy membrane. The thickness of an absorber layer must be in the range of several tens of micrometers in order to obtain a contrast of more than 100 for the conventional DXRL process at the Pohang Light Source (PLS). However, a 3 µm thick absorber layer can provide a sufficient contrast if the modified DXRL of the central beam-stop method is used, which blocks high-energy x-rays. A nano shadow mask with 30 nm sized apertures is fabricated and a nano x-ray shadow mask with 250 nm sized apertures is fabricated by depositing a 3 µm thick absorber layer on a nano shadow mask with 500 nm sized apertures. HAR-nano structures (circles with a diameter of 420 nm and lines with a width of 274 nm) with aspect ratios of over 10:1 on a 3.2 µm SU-8 are successfully fabricated by using the nano x-ray shadow mask and the central beam-stop method.
  • Glass coating for PDMS microfluidic channels by sol–gel methods, A.R. Abate et al. (2008)
    TitleGlass coating for PDMS microfluidic channels by sol–gel methods
    Authors A.R. Abate, D. Lee, T. Do, C. Holtze, D.A. Weitz
    PublicationLab on a Chip
    AbstractSoft lithography using polydimethylsiloxane (PDMS) allows one to fabricate complex microfluidic devices easily and at low cost. However, PDMS swells in the presence of many organic solvents significantly degrading the performance of the device. We present a method to coat PDMS channels with a glass-like layer using sol–gel chemistry. This coating greatly increases chemical resistance of the channels; moreover, it can be functionalized with a wide range of chemicals to precisely control interfacial properties. This method combines the ease of fabrication afforded by soft-lithography with the precision control and chemical robustness afforded by glass.
  • Fabrication of polymer microstructures for MEMS: sacrificial layer micromolding and patterned substrate micromolding, Ferrell et al. (2007)
    TitleFabrication of polymer microstructures for MEMS: sacrificial layer micromolding and patterned substrate micromolding
    Authors Ferrell, Woodard, Hansford
    PublicationBiomedical Microdevices
    DateDecember 26, 2007
    AbstractTwo soft lithography based fabrication techniques are employed for fabricating mechanically independent, freely suspended polymer microstructure from poly(n-propyl methacrylate) (PPMA), poly(methyl methacrylate) (PMMA), and polystyrene. Both methods involve a micromolding process followed by thermal bonding to the substrate. The first method, sacrificial layer micromolding, uses a water soluble sacrificial layer, allowing functional structures to be released by immersion in water. The second method, patterned substrate micromolding, uses a permanent substrate patterned via photolithography. Functional regions of the polymer MEMS are suspended over the voids in the photoresist pattern. The processes have been applied to the fabrication of polymer microstructures with a variety of geometries for specific applications. Devices have included microcantilevers, beams, and other more complicated microstuctures. The thermal molding process is conceivably applicable to the fabrication of microstructures from a wide variety of thermoplastic polymers, allowing material selection to be tailored based on application.
  • Photodefinable polydimethylsiloxane (PDMS) for rapid lab-on-a-chip prototyping, Ali Asgar S. Bhagat et al. (2007)
    TitlePhotodefinable polydimethylsiloxane (PDMS) for rapid lab-on-a-chip prototyping
    AuthorsAli Asgar S. Bhagat, Preetha Jothimuthu, Ian Papautsky
    PublicationLab on a Chip
    DateSep, 2007
    AbstractIn this paper, we introduce a new and simple method of patterning polydimethylsiloxane (PDMS) directly using benzophenone as a photoinitiator. The photodefinable PDMS mixture (photoPDMS) is positive-acting and only sensitive to light below 365 nm, permitting processing under normal ambient light. Features of the order of 100 [micro sign]m, which are sufficiently small for most microfluidic applications, were successfully fabricated using this novel process. A parametric study of process parameters was performed to optimize the fabrication. As a demonstration, microfluidic channels of varying dimensions were successfully fabricated using this process and experimentally characterized using fluorescence microscopy. To further demonstrate photoPDMS potential, thin (<30 [micro sign]m) free-standing films with through patterns were fabricated and successfully used as shadow masks. The photoPDMS process completely eliminates the need for a master, permits processing under normal ambient light conditions, and makes fabrication fast and simple. This process for rapid prototyping of low-cost, disposable LOCs can be accomplished without cleanroom facilities and thus can be employed for a wide range of applications.
  • Pneumatically actuated elastomeric device for nanoscale surface patterning, Shifeng Li et al. (2007)
    TitlePneumatically actuated elastomeric device for nanoscale surface patterning
    AuthorsShifeng Li, Timothy M. Dellinger, Qin Wang, Sandra Szegedi, Chang Liu
    PublicationApplied Physics Letters
    DateJuly 09, 2007
  • Photosensitive Poly(Dimethylsiloxane) (Photopdms) for Rapid and Simple Polymer Fabrication, Ali Asgar S. Bhagat et al. (2007)
    TitlePhotosensitive Poly(Dimethylsiloxane) (Photopdms) for Rapid and Simple Polymer Fabrication
    AuthorsAli Asgar S. Bhagat, Preetha Jothimuthu, Ian Papautsky
    DateJune 2007
    Conference NameSolid-State Sensors, Actuators and Microsystems Conference, 2007. TRANSDUCERS 2007. International
    AbstractIn this paper, we report a new and simple method of patterning polydimethylsiloxane (PDMS) directly under normal ambient light for rapid prototyping of disposable microfluidic lab-on-a-chips (LOCs). The photodefinable PDMS (photoPDMS) is positive-acting and only sensitive to light below 365 nm, which permits processing outside a gold room. A parametric study was conducted to optimize this novel fabrication technique. Features as small as 100 ¿m were successfully fabricated using photoPDMS. To further demonstrate the potential of this novel technique, thin (< 30 ¿m) free-standing patterned PDMS films. Successful demonstration of this novel process presents a feasibly simpler alternative approach for rapid prototyping of disposable microfluidic biochips for lab-on-a-chip applications.
  • Magnetically Actuated Nanorod Arrays as Biomimetic Cilia, B.A. Evans et al. (2007)
    TitleMagnetically Actuated Nanorod Arrays as Biomimetic Cilia
    AuthorsB.A. Evans, A.R. Shields, R.L. Carroll, S. Washburn, M.R. Falvo, R. Superfine
    PublicationNano Letters
    DateMay 9, 2007
    AbstractWe present a procedure for producing high-aspect-ratio cantilevered micro- and nanorod arrays of a PDMS-ferrofluid composite material. The rods have been produced with diameters ranging from 200 nm to 1 m and aspect ratios as high as 125. We demonstrate actuation of these superparamagnetic rod arrays with an externally applied magnetic field from a permanent magnet and compare this actuation with a theoretical energy-minimization model. The structures produced by these methods may be useful in microfluidics, photonic, and sensing applications.
  • A Rapid and Low-Cost Procedure for Fabrication of Glass Microfluidic Devices, Q. Chen et al. (2007)
    TitleA Rapid and Low-Cost Procedure for Fabrication of Glass Microfluidic Devices
    AuthorsQ. Chen, G. Li, Q.-H. Jin, J.-L. Zhao, Q.-S. Ren, Y.-S. Xu
    PublicationJournal of Microelectromechanical Systems
    AbstractIn this paper, we present a simple, rapid, and low-cost procedure for fabricating glass microfluidic chips. This procedure uses commercially available microscopic slides as substrates and a thin layer of AZ 4620 positive photoresist (PR) as an etch mask for fabricating glass microfluidic components, rather than using expensive quartz glasses or Pyrex glasses as substrates and depositing an expensive metal or polysilicon/amorphous silicon layer as etch masks in conventional method. A long hard-baking process is proposed to realize the durable PR mask capable of withstanding a long etching process. In order to remove precipitated particles generated during the etching process, a new recipe of buffered oxide etching with addition of 20% HCl is also reported. A smooth surface microchannel with a depth of more than 110 $muhboxm$ is achieved after 2 h of etching. Meanwhile, a simple, fast, but reliable bonding process based on UV-curable glue has been developed which takes only 10 min to accomplish the efficient sealing of glass chips. The result shows that a high bonding yield ( $sim$100%) can be easily achieved without the requirement of clean room facilities and programmed high-temperature furnaces. The presented simple fabrication process is suitable for fast prototyping and manufacturing disposable microfluidic devices.$hfill$ [2007-0032]
  • Fabrication of complex nanoscale structures on various substrates, Kang-Soo Han et al. (2007)
    TitleFabrication of complex nanoscale structures on various substrates
    AuthorsKang-Soo Han, Sung-Hoon Hong, Heon Lee
    PublicationApplied Physics Letters
  • Fabrication of beam structures with micro-scale cross-sections and meso-scale spans, Michael James Martin et al. (2007)
    TitleFabrication of beam structures with micro-scale cross-sections and meso-scale spans
    AuthorsMichael James Martin, Robert D. White, Katsuo Kurabayashi, Iain D. Boyd
    PublicationJournal of Micromechanics and Microengineering
    AbstractTo allow testing of micro-scale aerodynamics, a process was created to manufacture beam structures that combine spans of 1 cm with a cross-section of 5 µm by 100 µm. The structural considerations limiting the fabrication of a structure combining macro-scale spans with a micro-scale cross-section are analyzed. Limiting considerations include forces during operation, fluid forces during release, vibrational limitations and beam buckling. Based on these results, a fabrication process for creating a beam structure for large spans without support structures is devised, incorporating the use of back-side etches and extra handling wafers to avoid stiction. This process is used to successfully fabricate the desired structure.
  • Design and microfabrication of a high-aspect-ratio PDMS microbeam array for parallel nanonewton force measurement and protein printing, F. M. Sasoglu et al. (2007)
    TitleDesign and microfabrication of a high-aspect-ratio PDMS microbeam array for parallel nanonewton force measurement and protein printing
    AuthorsF. M. Sasoglu, A. J. Bohl, B. E. Layton
    PublicationJournal of Micromechanics and Microengineering
    AbstractCell and protein mechanics has applications ranging from cellular development to tissue engineering. Techniques such as magnetic tweezers, optic tweezers and atomic force microscopy have been used to measure cell deformation forces of the order of piconewtons to nanonewtons. In this study, an array of polymeric polydimethylsiloxane (PDMS) microbeams with diameters of 10-40 µm and lengths of 118 µm was fabricated from Sylgard® with curing agent concentrations ranging from 5% to 20%. The resulting spring constants were 100-300 nN µm[?]1. The elastic modulus of PDMS was determined experimentally at different curing agent concentrations and found to be 346 kPa to 704 kPa in a millimeter-scale array and [?]1 MPa in a microbeam array. Additionally, the microbeam array was used to print laminin for the purpose of cell adhesion. Linear and nonlinear finite element analyses are presented and compared to the closed-from solution. The highly compliant, transparent, biocompatible PDMS may offer a method for more rapid throughput in cell and protein mechanics force measurement experiments with sensitivities necessary for highly compliant structures such as axons.
  • Fabrication of SU-8 free-standing structures embedded in microchannels for microfluidic control, A. Ezkerra et al. (2007)
    TitleFabrication of SU-8 free-standing structures embedded in microchannels for microfluidic control
    AuthorsA. Ezkerra, L. J. Fernández, K. Mayora, J. M. Ruano-López
    PublicationJournal of Micromechanics and Microengineering
    AbstractThe application of cantilevered structures as check valves or flow sensors can provide new possibilities towards the integration of accurate sample preparation systems within a lab-on-a-chip. The cantilevers presented in this paper act as flaps enclosed within a channel in a direction perpendicular to the flow. This orientation allows simpler designs and easier integration of the valve or flow sensor within the microfluidic network. The cantilevers have been embedded in a microfluidic channel by low temperature full wafer adhesive bonding. In this way, electrodes, microchannels, microchambers and cantilevers can be fabricated and sealed at the same time at a wafer level. To the author's knowledge, this is the first example of flap cantilevers embedded in a polymeric microfluidic channel. The mobility of the structure and the leakage are dependent on the size of the sealing gaps between the cantilever and the enclosing channel. In this paper, we present three different fabrication methods for a range of bottom sealing gaps from the micro to the nanometer size. The top sealing gap is determined by the adhesive bonding and is 11 µm wide. Furthermore, various geometrical features have been introduced in order to optimize a valve or flow sensor. The characterization of the structures comprises measurements of the sensitivity of each cantilever design by obtaining their relative spring constant, measurements of their elastic and plastic working regimes and Young's modulus of the SU-8.
  • Sylgard® 184 Silicone Elastomer, Solar Product Information, Dow Corning Corporation (2007)
    TitleSylgard® 184 Silicone Elastomer, Solar Product Information
    AuthorDow Corning Corporation
    AbstractTwo-part silicone that cures to a flexible elastomer for protection of electrical and electronic devices in solar applications
  • Microfabrication of cavities in polydimethylsiloxane using DRIE silicon molds, Ut-Binh T. Giang et al. (2007)
    TitleMicrofabrication of cavities in polydimethylsiloxane using DRIE silicon molds
    AuthorsUt-Binh T. Giang, Dooyoung Lee, Michael R. King, Lisa A. DeLouise
    PublicationLab on a Chip
    AbstractWe present a novel method to create cavities in PDMS that is simple and exhibits wide process latitude allowing control over the radius of curvature to form shallow concave pits or deep spherical cavities.
  • Integration of large-area polymer nanopillar arrays into microfluidic devices using in situ polymerization cast molding, Guofang Chen et al. (2007)
    TitleIntegration of large-area polymer nanopillar arrays into microfluidic devices using in situ polymerization cast molding
    AuthorsGuofang Chen, Gregory T. McCandless, Robin L. McCarley, Steven A. Soper
    PublicationLab on a Chip
    AbstractPresented here is a simple and robust approach for the integration of mixed-scale (nm-cm) structures into fluidic devices. We report on devices composed of large-area polymer nanopillar arrays of high aspect ratio (33-667) integrated into microfluidic channels fabricated by cast-molding polymerization of methyl methacrylate with mechanically/lithographically patterned, nanoporous aluminium oxide (AAO) templates. The microchannels containing the nanopillar arrays can be chemically functionalized and used for a variety of applications, such as separation beds or solid-phase reactors/extractors.
  • Poly(vinyl alcohol) as a structure release layer for the microfabrication of polymer composite structures, Kweku A. Addae-Mensah et al. (2007)
    TitlePoly(vinyl alcohol) as a structure release layer for the microfabrication of polymer composite structures
    AuthorsKweku A. Addae-Mensah, Ronald S. Reiserer, John P. Wikswo
    PublicationJournal of Micromechanics and Microengineering
    AbstractWhile lift-off techniques are common in the fabrication of hard, silicon-based microelectromechanical systems (MEMS), these techniques are not yet in widespread use in soft lithography, where polymer materials are used to fabricate MEMS devices for biological applications (bioMEMS). We present fabrication steps that allow us to make use of poly(vinyl alcohol) as a structure release agent in bioMEMS microfabrication. The release method offers a simple, cost effective and reliable way to release microfabricated structures that need to be bonded to other structures or are already bonded to them. We use this technique to release discs made of SU-8 that are attached to a vertical cylindrical microcantilever array that is replica molded using polydimethylsiloxane (PDMS). This approach may be used to release structures made from a variety of materials that are not compatible with typical lift-off chemistries, although we address only SU-8 and PDMS in this technical note.
  • Photosensitive poly(dimethylsiloxane) materials for microfluidic applications, Katerina Tsougeni et al. (2007)
    TitlePhotosensitive poly(dimethylsiloxane) materials for microfluidic applications
    AuthorsKaterina Tsougeni, Angeliki Tserepi, Evangelos Gogolides
    PublicationMicroelectron. Eng
    AbstractPoly(dimethylsiloxane) (PDMS) is used as a thermally crosslinked material in microfluidics and Bio-MEMS. Recently photo-patternable materials show increasing interest, as the demand for easy alignment arises for multilayered structures. We present a photopatterning process for PDMS in microfluidics, for two main uses: (a) as a thin (approximately 10@mm) structural layer, and (b) as a very thin (approximately 1@mm) hard mask for oxygen plasma etching of microfluidic polymeric substrates down to several tens of microns. We study the deep-UV and I-line photocrosslinking properties of siloxane copolymers containing vinyl-methyl-siloxane groups as polymerizable units. These materials are sensitive to DUV and can be sensitized to 300-400nm using free radical initiators. We prove that even thermally curable PDMS (Sylgard 184, base) can become photosensitive in DUV, although its practical use is limited to very thin films, due to its small molecular weight.
  • Characterization of poly(isobornyl acrylate) as a construction material for microfluidic applications, M. d.C López-García et al. (2007)
    TitleCharacterization of poly(isobornyl acrylate) as a construction material for microfluidic applications
    AuthorsM. d.C López-García, D. J Beebe, W. C Crone
    PublicationJournal of Applied Polymer Science
    AbstractIsobornyl acrylate (IBA) is a photopolymerizable monomer that is employed in microfluidic devices because of desirable properties, such as inertness, transparency, and resolution. However, some of the mechanical properties of poly(isobornyl acrylate) are greatly affected by subtle changes in the manufacturing techniques. In this study, the parameters of exposure time, UV intensity, and aging are varied to study their effect on the material properties of thin samples of isobornyl acrylate construction material (&lt;0.25 mm). Mechanical testing was used to obtain properties, such as elasticity, maximum strength, and maximum strain. It was observed that when using high levels of both exposure time and intensity, the polymers strength was increased. Lowering one of these two parameters immediately reduced the construction materials strength. It was also noted that aging weakens the material in as little as 1 day. In addition, an anisotropic response that produces curling in samples has been studied. It showed to have a negligible effect on the mechanical properties of the material; however it may have a major effect on device quality and shelf-life. \textcopyright 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007
  • Stretched Polymer Nanohairs by Nanodrawing, H.E. Jeong et al. (2006)
    TitleStretched Polymer Nanohairs by Nanodrawing
    AuthorsH.E. Jeong, S.H. Lee, P. Kim, K.Y. Suh
    PublicationNano Letters
    DateJuly 12, 2006
    AbstractA simple, yet innovative, method is presented for fabricating high-aspect-ratio polymer nanohairs (aspect ratio >20) on a solid substrate by sequential application of molding and drawing of a thin polymer film. The polymer film was prepared by spin coating on a rigid or flexible substrate, and the temperature was raised above the polymer's glass transition while in conformal contact with a poly(urethane acrylate) mold having nanocavities. Consequently, capillary forces induced deformation of the polymer melt into the void spaces of the mold and the filled nanostructure was further elongated upon removal of the mold due to tailored adhesive force at the mold/polymer interface. The optimum value of the work of adhesion at the mold/polymer interface ranged from 0.9 to 1.1 times that at the substrate/polymer interface.
  • Kinetic investigations on the UV-induced photopolymerization of nanocomposites by FTIR spectroscopy, Fusheng Li et al. (2006)
    TitleKinetic investigations on the UV-induced photopolymerization of nanocomposites by FTIR spectroscopy
    AuthorsFusheng Li, Shuxue Zhou, Bo You, Limin Wu
    PublicationJournal of Applied Polymer Science
    AbstractThe kinetics of the photopolymerization for nanocomposites containing nanosilica with 2,2-dimethoxy-1,2-diphenylethan-1-one or benzophenone/n-methyl diethanolamine (BP/MDEA)as photoinitiators were studied by FTIR spectroscopy. It was found that nanocomposites containing nanosilica had higher conversion in comparison with pristine EA. The presence of MPS and ethanol accelerated the photopolymerization of nanocomposites, while the presence of water decelerated it. The photopolymerization of nanocomposites was more sensitive to oxygen than that of pristine EA. � 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99:1429-1436, 2006
  • Solvent-resistant elastomeric microfluidic devices and applications, R. van Dam (2005)
    TitleSolvent-resistant elastomeric microfluidic devices and applications
    AuthorR. van Dam
    AbstractMicrofluidics is increasingly being used in many areas of biotechnology and chemistry to achieve reduced reagent volumes, improved performance, integration, and parallelism, among other advantages. Though early devices were based on rigid materials such as glass and silicon, elastomeric materials such as polydimethylsiloxane (PDMS) are rapidly emerging as a ubiquitous platform for applications in biotechnology. This is due, in part, to simpler fabrication procedures and to the ability to integrate mechanical microvalves at vastly greater densities. For many applications in the areas of chemical synthesis and analysis, however, PDMS cannot replace glass and silicon due to its incompatibility with many solvents and reagents. Such areas could benefit tremendously from the development of an elastomeric microfluidic device technology that combines the advantages of PDMS with the property of solvent resistance. Simplified fabrication could increase the accessibility of microfluidics, and the possibility of dense valve integration could lead to significant advances in device sophistication. Applications could be more rapidly developed by design re-use due to the independence of mechanical valves on fluid properties (unlike electrokinetic pumping), and the property of permeability could enable novel fluidic functions for accessing a broader range of reactions than is possible in glass and silicon. The first half of this thesis describes our strategies and efforts to develop this new enabling technology. Several approaches are presented in Chapter 3, and two particularly successful ones, based on new elastomers (FNB and PFPE), are described in Chapters 4 and 5. Chapter 6 describes a novel method of fabricating devices from 3D molds that could expand the range of useful elastomers. The second half of this thesis discusses microfluidic combinatorial synthesis and high throughput screening—applications that take particular advantage of the ability to integrate thousands of individual valves and reaction chambers. Chapter 7 introduces several scalable device architectures and presents results of preliminary steps toward the synthesis of combinatorial DNA and peptide arrays. A novel method of performing universal gene expression analysis with combinatorial DNA arrays is described in Chapter 8 and an algorithm for predicting relationships among genes from gene expression array data is presented in Chapter 9.
  • Characterization of Polydimethylsiloxane (PDMS) Properties for Biomedical Micro/Nanosystems, Mata et al. (2005)
    TitleCharacterization of Polydimethylsiloxane (PDMS) Properties for Biomedical Micro/Nanosystems
    Authors Mata, Fleischman, Roy
    PublicationBiomedical Microdevices
    DateDecember 08, 2005
    AbstractPolydimethylsiloxane (PDMS Sylgard 184, Dow Corning Corporation) pre-polymer was combined with increasing amounts of cross-linker (5.7, 10.0, 14.3, 21.4, and 42.9 wt.%) and designated PDMS1, PDMS2, PDMS3, PDMS4, and PDMS5, respectively. These materials were processed by spin coating and subjected to common microfabrication, micromachining, and biomedical processes: chemical immersion, oxygen plasma treatment, sterilization, and exposure to tissue culture media. The PDMS formulations were analyzed by gravimetry, goniometry, tensile testing, nanoindentation, scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS). Spin coating of PDMS was formulation dependent with film thickness ranging from 308 μm on PDMS1 to 171 μm on PDMS5 at 200 revolutions per minute (rpm). Ultimate tensile stress (UTS) increased from 3.9 MPa (PDMS1) to 10.8 MPa (PDMS3), and then decreased down to 4.0 MPa (PDMS5). Autoclave sterilization (AS) increased the storage modulus (σ) and UTS in all formulations, with the highest increase in UTS exhibited by PDMS5 (218%). PDMS surface hydrophilicity and micro-textures were generally unaffected when exposed to the different chemicals, except for micro-texture changes after immersion in potassium hydroxide and buffered hydrofluoric, nitric, sulfuric, and hydrofluoric acids; and minimal changes in contact angle after immersion in hexane, hydrochloric acid, photoresist developer, and toluene. Oxygen plasma treatment decreased the contact angle of PDMS2 from 109∘ to 60∘. Exposure to tissue culture media resulted in increased PDMS surface element concentrations of nitrogen and oxygen.
  • Negative Tone Photoresist Series ma-N 1400 - processing guidelines, Micro Resist Technology GmbH (2005)
    TitleNegative Tone Photoresist Series ma-N 1400 - processing guidelines
    AuthorMicro Resist Technology GmbH
  • Stability of Microfabricated High Aspect Ratio Structures in Poly(dimethylsiloxane), P. Roca-Cusachs et al. (2005)
    TitleStability of Microfabricated High Aspect Ratio Structures in Poly(dimethylsiloxane)
    AuthorsP. Roca-Cusachs, F. Rico, E. Martinez, J. Toset, R. Farre, D. Navajas
    DateJune 7, 2005
    AbstractThe stability of structures microfabricated in soft elastomeric polymers is an important concern in most applications that use these structures. Although relevant for several applications, the collapse to the ground of high aspect ratio structures (ground collapse) is still poorly understood. The stability of soft microfabricated high aspect ratio structures versus ground collapse was experimentally assessed, and a new model of ground collapse involving adhesion was developed. Sets of posts with diameters from 0.36 to 2.29 m were fabricated in poly(dimethylsiloxane) and tested in air or immersed in water and ethanol to change the work of adhesion. The critical aspect ratio (the highest length-to-width ratio for which a post is not at risk of collapsing) was determined as a function of the diameter. The critical aspect ratio in air ranged from 2 to 4 and increased with the diameter. Work of adhesion was found to be determinant for and inversely correlated to stability. These results highlight the role played by adhesion and offer the possibility of improving stability by reducing the work of adhesion. The ground collapse model developed accounted for the main features of structure stability. The results indicate that ground collapse can be a limiting factor in the design of soft polymer structures.
  • Fine pattern transfer by nanocasting lithography, Yoshihiko Hirai et al. (2005)
    TitleFine pattern transfer by nanocasting lithography
    AuthorsYoshihiko Hirai, Takashi Yoshikawa, Masatoshi Morimatsu, Masaki Nakajima, Hiroaki Kawata
    PublicationMicroelectronic Engineering
    DateMarch 2005
    AbstractA novel pattern transfer technique has been demonstrated by simple procedure based on a nanoimprint lithography. A polymer is coated on a mold by a spin coater and cast into fine grooves on the mold. After evaporation of a solvent, an adhesive resin is coated on the polymer and put a substrate plate. After releasing the mold, fine pattern is successfully transferred to the polymer. Applying this process, fine pattern transfer using various polymers, high aspect ratio pattern and sub-100�nm patterns have been demonstrated on various substrates.
  • A single layer negative tone lift-off photo resist for patterning a magnetron sputtered Ti/Pt/Au contact system and for solder bumps, A. Voigt et al. (2005)
    TitleA single layer negative tone lift-off photo resist for patterning a magnetron sputtered Ti/Pt/Au contact system and for solder bumps
    AuthorsA. Voigt, M. Heinrich, K. Hauck, R. Mientus, G. Gruetzner, M. T�pper, O. Ehrmann
    PublicationMicroelectronic Engineering
    DateMarch 2005
    AbstractIn this paper, we present the suitability of easy to handle negative tone photoresists providing examples of lift-off applications. The lithographic process of this single layer resist system requires standard broadband or i-line process conditions. At first, the capability to obtain an undercut pattern and the thermal stability of the resist ma-N 1400 is demonstrated in the lift-off patterning of magnetron sputtered thin three layer contact system Ti/Pt/Au. Temperature of the substrate during sputtering was measured time-resolved using a thermal couple. Secondly, an example to achieve AuSn solder bumps of 7.5�[mu]m diameter by a combination of sputtering and metal evaporation using the lift-off resist ma-N 400 is given. Regarding the further miniaturization of electronic devices, this process is a cost-effective method to achieve solder depots for flip chip bonding of ultra thin chips.
  • Studies of spin-coated polymer films, K. Norrman et al. (2005)
    TitleStudies of spin-coated polymer films
    AuthorsK. Norrman, A. Ghanbari-Siahkali, N. B. Larsen
    PublicationAnnual Reports Section "C" (Physical Chemistry)
    AbstractSpin-coating is widely employed for the highly reproducible fabrication of thin film coatings over large areas with high structural uniformity. Research in recent years has extended the scope of spin-coating by chemically engineering the interface of support and solution to obtain specific structural order in the resulting supported thin films. This review will discuss both the fundamental physical and chemical processes governing the conventional spin-coating process and describe methodologies for the preparation of spin-coated polymer thin films. Furthermore, a range of advanced applications and recent developments within this field will be reviewed with focus on engineering chemical and topological structure during the coating process.
  • Manufacture of high-aspect-ratio micro-hair sensor arrays, G. J. Schmitz et al. (2005)
    TitleManufacture of high-aspect-ratio micro-hair sensor arrays
    AuthorsG. J. Schmitz, Ch Brücker, P. Jacobs
    PublicationJournal of Micromechanics and Microengineering
    AbstractArrays of microposts or micropillars find a variety of applications and one of their key properties is the aspect ratio (AR) of the individual posts. This parameter, for example, determines the sensitivity of micropost force field sensors. A concept for the manufacture of arrays of micro-hairs is presented allowing us to create extremely high AR of the filiform micro-hairs. The concept is based on a 'lost mould process' allowing for frictionless de-moulding of the sensor array by melting respectively dissolution of a mould. Such a 'lost mould process' requires an inexpensive manufacture of the moulds. Moulds were thus prepared by laser drilling of wax foils. The concept has been applied to the manufacture of micro-hairs from poly(dimethylsiloxane) (PDMS) elastomers and aspect ratios close to 20 have been achieved. The basic concept is not restricted to elastomers but can be adapted to other types of materials.
  • Information about Dow Corning® brand Silicone Encapsulants, Dow Corning Corporation (2005)
    TitleInformation about Dow Corning® brand Silicone Encapsulants
    AuthorDow Corning Corporation
  • Temperature-Sensitive Hybrid Microgels with Magnetic Properties, A. Pich et al. (2004)
    TitleTemperature-Sensitive Hybrid Microgels with Magnetic Properties
    AuthorsA. Pich, S. Bhattacharya, Y. Lu, V. Boyko, H.-J.P. Adler
    DateNovember 23, 2004
    AbstractIn the present paper, we report the preparation of hybrid temperature-sensitive microgels which include magnetite nanoparticles in their structure. Polymeric microgels have been prepared by surfactant-free emulsion copolymerization of acetoacetoxyethyl methacrylate (AAEM) and N-vinylcaprolactam (VCL) in water with a water-soluble azo-initiator. The obtained microgels possess a low critical solution temperature (LCST) in water solutions, with a rapid decrease of the particle size being observed at elevated temperatures. Magnetite was deposited directly into microgels, leading to the formation of composite particles which combine both temperature-sensitive and magnetic properties. The influence of magnetite load on microgel size, morphology, swelling-deswelling behavior, and stability is discussed.
  • ma-N 400 and ma-N 1400 Photoresists - technology for Lift-Off Process, Micro Resist Technology GmbH (2004)
    Titlema-N 400 and ma-N 1400 Photoresists - technology for Lift-Off Process
    AuthorMicro Resist Technology GmbH
    Date2 july 2004
    AbstractThe ma-N 400 and ma-N 1400 are an innovation in negative tone photoresists for flexible use for proximity and contact exposure. Full application compatibility with processing of conventional positive tone photoresists is guaranteed. Adjustable negative sidewalls can be created by a simple lithographic process. The generation of more than 1000 nm metal structures by the lift-off process is achievable.
  • An Ultraviolet-Curable Mold for Sub-100-nm Lithography, S. Choi et al. (2004)
    TitleAn Ultraviolet-Curable Mold for Sub-100-nm Lithography
    AuthorsS. Choi, P.J. Yoo, S.J. Baek, T.W. Kim, H.H. Lee
    PublicationJournal of the American Chemical Society
    DateJune 30, 2004
    AbstractWe describe a novel UV-curable mold that is stiff enough for replicating dense sub-100-nm features even with a high aspect ratio. It also allows for flexibility when the mold is prepared on a flexible support such that large area replication can be accomplished. The composite material of the mold is inert to chemicals and solvents. The surface energy is made low with a small amount of releasing agent such that the mold can be removed easily and cleanly after patterning. In addition, the material allows self-replication of the mold. These unique features of the mold material should make the mold quite useful for various patterning purposes.
  • Elastomer-supported cold welding for room temperature wafer-level bonding, W.Y. Zhang et al. (2004)
    TitleElastomer-supported cold welding for room temperature wafer-level bonding
    AuthorsW.Y. Zhang, G.S. Ferguson, S. Tatic-Lucic
    Conference NameMicro Electro Mechanical Systems, 2004. 17th IEEE International Conference on. (MEMS)
    AbstractThis paper presents a method for room-temperature wafer-level bonding that is applicable for the MEMS and NEMS packaging and fabrication processes, but does not require an applied voltage, high pressure or vacuum. By applying a layer of elastomer between the wafer and gold overlayer, we successfully bonded two silicon wafers under limited load (/spl sim/3 KPa) at room temperature (25/spl deg/C). One of the important potential applications of this technique is to create a temporary cap wafer that would protect already released, bulk or surface-micromachined structures during the dicing process. The initial results of experiments on the detachment of the temporary cap wafers bonded using this method are presented.
  • Unconventional nanofabrication, B.D. Gates et al. (2004)
    TitleUnconventional nanofabrication
    AuthorsB.D. Gates, Q.B. Xu, J.C. Love, D.B. Wolfe, G.M. Whitesides
    PublicationAnnual review of materials research
    AbstractNanostructures are fabricated using either conventional or unconventional tools-that is, by techniques that are highly developed and widely used or by techniques that are relatively new and still being developed. This chapter reviews techniques of unconventional nanofabrication, and focuses on experimentally simple and inexpensive approaches to pattern features with dimensions < 100 nm. The techniques discussed include soft lithography, scanning probe lithography, and edge lithography. The chapter includes recent advances in fabricating nanostructures using each set of techniques, together with demonstrated advantages, limitations, and applications for each.
  • Solvent Compatibility of Poly(dimethylsiloxane)-Based Microfluidic Devices, J.N. Lee et al. (2003)
    TitleSolvent Compatibility of Poly(dimethylsiloxane)-Based Microfluidic Devices
    AuthorsJ.N. Lee, C. Park, G.M. Whitesides
    PublicationAnalytical Chemistry
    DateDecember 1, 2003
    AbstractThis paper describes the compatibility of poly(dimethylsiloxane) (PDMS) with organic solvents; this compatibility is important in considering the potential of PDMS-based microfluidic devices in a number of applications, including that of microreactors for organic reactions. We considered three aspects of compatibility: the swelling of PDMS in a solvent, the partitioning of solutes between a solvent and PDMS, and the dissolution of PDMS oligomers in a solvent. Of these three parameters that determine the compatibility of PDMS with a solvent, the swelling of PDMS had the greatest influence. Experimental measurements of swelling were correlated with the solubility parameter, (cal1/2 cm-3/2), which is based on the cohesive energy densities, c (cal/cm3), of the materials. Solvents that swelled PDMS the least included water, nitromethane, dimethyl sulfoxide, ethylene glycol, perfluorotributylamine, perfluorodecalin, acetonitrile, and propylene carbonate; solvents that swelled PDMS the most were diisopropylamine, triethylamine, pentane, and xylenes. Highly swelling solvents were useful for extracting contaminants from bulk PDMS and for changing the surface properties of PDMS. The feasibility of performing organic reactions in PDMS was demonstrated by performing a Diels-Alder reaction in a microchannel.
  • A Photocurable Poly(dimethylsiloxane) Chemistry Designed for Soft Lithographic Molding and Printing in the Nanometer Regime, K.M. Choi et al. (2003)
    TitleA Photocurable Poly(dimethylsiloxane) Chemistry Designed for Soft Lithographic Molding and Printing in the Nanometer Regime
    AuthorsK.M. Choi, J.A. Rogers
    PublicationJournal of the American Chemical Society
    DateApril 9, 2003
    AbstractPatterning techniques that rely on high-resolution elastomeric elements such as stamps, molds, and conformable photomasks are operationally simple methods for nanofabrication that may find applications in areas such as molecular and organic electronics. The resolution of these "soft" lithographic procedures is often limited by the mechanical properties of the elastomers. We introduce here a chemically modified poly(dimethylsiloxane) material that is designed and optimized specifically for soft lithography, particularly in the nanometer regime. We demonstrate its use for nanopatterning tasks that are challenging with the commercially available elastomers that have been used in the past.
  • Rapid replication of polymeric and metallic high aspect ratio microstructures using PDMS and LIGA technology, K. Kim et al. (2002)
    TitleRapid replication of polymeric and metallic high aspect ratio microstructures using PDMS and LIGA technology
    AuthorsK. Kim, S. Park, J.-B. Lee, H. Manohara, Y. Desta, M. Murphy, C. H. Ahn
    PublicationMicrosystem Technologies
    DateNovember 04, 2002
    Abstract This paper present a method of rapid replication of polymeric high aspect ratio microstructures (HARMs) and a method of rapid reproduction of metallic micromold inserts for HARMs using polydimethylsiloxane (PDMS) casting and standard LIGA processes. A high aspect ratio (HAR) metallic micromold insert, featuring a variety of test microstructures made of electroplated nickel with 15:1 height-to-width ratio for 300 μm microstructures, was fabricated by the standard LIGA process using deep X-ray lithography (DXRL). A 10:1 mixture of pre-polymer PDMS and a curing agent were cast onto the HAR metallic micromold insert, cured and peeled off to create reverse images of the HAR metallic micromold insert in PDMS. In addition to the replication of polymeric HARMs, replicated PDMS HARMS were coated with a metallic sacrificial layer and electroplated in nickel to reproduce another metallic micromold insert. This method can be used to rapidly and massively reproduce HAR metallic micromold inserts in low cost mass production manner without further using DXRL.
  • High-frequency ultrasound array element using thermoelastic expansion in an elastomeric film, T. Buma et al. (2001)
    TitleHigh-frequency ultrasound array element using thermoelastic expansion in an elastomeric film
    AuthorsT. Buma, M. Spisar, M. O'Donnell
    PublicationApplied Physics Letters
    DateJuly 23, 2001
    AbstractThe thermoelastic effect was used to produce high-frequency, broadband ultrasound in water. A pulsed diode laser, followed by an erbium-doped fiber amplifier, was focused onto a light-absorbing film deposited on a glass substrate. Conversion efficiency was improved by over 20 dB using an elastomeric film instead of a more commonly used metallic one. Radiation pattern measurements show that considerable energy is radiated at +/–45° for frequencies beyond 50 MHz. These results show that the thermoelastic effect can be used to produce phased arrays for high-frequency ultrasound imaging.
  • Spin Coater Theory, Cost Effective Equipment (2000)
    TitleSpin Coater Theory
    AuthorCost Effective Equipment
    Date17 Oct 2000
    PublisherBrewer Science
    AbstractSpin coating has been used for several decades for the application of thin films. A typical process involves depositing a small puddle of a fluid resin onto the center of a substrate and then spinning the substrate at high speed (typically around 3000 rpm). Centripetal acceleration will cause most of the resin to spread to, and eventually off, the edge of the substrate, leaving a thin film of resin on the surface. Final film thickness and other properties will depend on the nature of the resin (viscosity, drying rate, percent solids, surface tension, etc.) and the parameters chosen for the spin process. Factors such as final rotational speed, acceleration, and fume exhaust contribute to how the properties of coated films are defined. One of the most important factors in spin coating is repeatability. Subtle variations in the parameters that define the spin process can result in drastic variations in the coated film. The following is an explanation of some of the effects of these variations.
  • Siloxane Polymers for High-Resolution, High-Accuracy Soft Lithography, H. Schmid et al. (2000)
    TitleSiloxane Polymers for High-Resolution, High-Accuracy Soft Lithography
    AuthorsH. Schmid, B. Michel
    DateApril 18, 2000
    AbstractWe report the formulation of siloxane polymers for high-resolution, high-accuracy stamps for soft lithography. With this technique, a molecular, polymeric, or liquid ink is applied to the surface of a stamp and then transferred by conformal contact to a substrate. Stamps for this technique are usually made of a commercial siloxane elastomer with appropriate mechanical properties to achieve conformal contact but are incapable of printing accurate, submicrometer patterns. To formulate better stamp polymers, we used models of rubber-like elasticity as guidelines. Poly(dimethylsiloxane) networks were prepared from vinyl and hydrosilane end-linked polymers and vinyl and hydrosilane copolymers, with varying mass between cross-links and junction functionality. The polymer formulations were characterized by strain at break as well as compression modulus and surface hardness measurements. This resulted in the identification of bimodal polymer networks having mechanical properties that allow the replication of high-density patterns at the 100 nm scale and that withstand the mechanical constraints during use as a stamp material. We also demonstrate advantageous implementations of the formulated polymers in hybrid stamps that achieve submicrometer-dimensional accuracy over large areas.
  • Fabrication of microfluidic systems in poly(dimethylsiloxane), J. Cooper McDonald et al. (2000)
    TitleFabrication of microfluidic systems in poly(dimethylsiloxane)
    AuthorsJ. Cooper McDonald, David C. Duffy, Janelle R. Anderson, Daniel T. Chiu, Hongkai Wu, Olivier J. A. Schueller, George M. Whitesides
    AbstractMicrofluidic devices are finding increasing application as analytical systems, biomedical devices, tools for chemistry and biochemistry, and systems for fundamental research. Conventional methods of fabricating microfluidic devices have centered on etching in glass and silicon. Fabrication of microfluidic devices in poly(dimethylsiloxane) (PDMS) by soft lithography provides faster, less expensive routes than these conventional methods to devices that handle aqueous solutions. These soft-lithographic methods are based on rapid prototyping and replica molding and are more accessible to chemists and biologists working under benchtop conditions than are the microelectronics-derived methods because, in soft lithography, devices do not need to be fabricated in a cleanroom. This paper describes devices fabricated in PDMS for separations, patterning of biological and nonbiological material, and components for integrated systems.
  • Replication and Compression of Surface Structures with Polydimethylsiloxane Elastomer, D. Campbell et al. (1999)
    TitleReplication and Compression of Surface Structures with Polydimethylsiloxane Elastomer
    AuthorsD. Campbell, K.J. Beckman, C.E. Calderon, P.W. Doolan, R.H. Moore, A.B. Ellis, G.C. Lisensky
    PublicationJournal of Chemical Education
    DateApril, 1999
    AbstractThis paper describes simple classroom demonstrations and laboratory experiments based on properties of polydimethylsiloxane (PDMS). PDMS is a colorless, transparent elastomer. Spheres cast from PDMS can be cross-linked to varying extents to affect their rigidity, as seen in their ability to bounce when dropped. PDMS recently has been used by Whitesides et al. to replicate submicron-scale patterns by casting a negative relief image from a master template, and to progressively reduce the dimensions of these patterns through cycles based on mechanical compression. Curing PDMS in contact with features pressed into aluminum foil transfers the foil features to the elastomer. The raised surface features of the resulting cured PDMS block can transfer ink images to paper in a fashion that is similar to microcontact printing processes. Stretching or compressing the block will alter the dimensions of the transferred image. Curing PDMS in contact with the microscopic features on optical transform slides can transfer the slide features to the elastomer. The feature spacings, altered by stretching or compressing the elastomer, can be determined through the optical transform experiment. Moreover, when the elastomer is suitably compressed, the features, now with reduced dimensions, can be transferred first to an epoxy resin and then to a new sample of PDMS, representing a cycle that can lead to progressively reduced feature spacings.
  • Aldrich Polymer Products Applicaton & Reference Information: Free Radical Initiators, Aldrich Chemical Co., Inc. (1999)
    TitleAldrich Polymer Products Applicaton & Reference Information: Free Radical Initiators
    Author Aldrich Chemical Co., Inc.
  • Re-configurable fluid circuits by PDMS elastomer micromachining, D. Armani et al. (1999)
    TitleRe-configurable fluid circuits by PDMS elastomer micromachining
    AuthorsD. Armani, C. Liu, N. Aluru
    Conference NameTwelfth IEEE International Conference on Micro Electro Mechanical Systems, 1999
    PlaceOrlando, FL, USA
    AbstractWe report on a microfabrication technique for realizing re-configurable micro fluidics devices using polymethylsiloxane material (PDMS). The mechanical characteristics of the material, including the Young's modulus and the adhesion energy have been determined experimentally. The magnitude of Young's modulus ranges from 8.7×105 Pa to 3.6×105 Pa. The adhesion energy is a function of the PDMS composition as well as chemical treatment. A method for efficiently developing flow interconnects has been demonstrated
  • Rapid Prototyping of Microfluidic Systems in Poly(dimethylsiloxane), D.C. Duffy et al. (1998)
    TitleRapid Prototyping of Microfluidic Systems in Poly(dimethylsiloxane)
    AuthorsD.C. Duffy, J.C. McDonald, O.J.A. Schueller, G.M. Whitesides
    PublicationAnalytical Chemistry
    DateDecember 1, 1998
    AbstractThis paper describes a procedure that makes it possible to design and fabricate (including sealing) microfluidic systems in an elastomeric material-poly(dimethylsiloxane) (PDMS)-in less than 24 h. A network of microfluidic channels (with width >20 m) is designed in a CAD program. This design is converted into a transparency by a high-resolution printer; this transparency is used as a mask in photolithography to create a master in positive relief photoresist. PDMS cast against the master yields a polymeric replica containing a network of channels. The surface of this replica, and that of a flat slab of PDMS, are oxidized in an oxygen plasma. These oxidized surfaces seal tightly and irreversibly when brought into conformal contact. Oxidized PDMS also seals irreversibly to other materials used in microfluidic systems, such as glass, silicon, silicon oxide, and oxidized polystyrene; a number of substrates for devices are, therefore, practical options. Oxidation of the PDMS has the additional advantage that it yields channels whose walls are negatively charged when in contact with neutral and basic aqueous solutions; these channels support electroosmotic pumping and can be filled easily with liquids with high surface energies (especially water). The performance of microfluidic systems prepared using this rapid prototyping technique has been evaluated by fabricating a miniaturized capillary electrophoresis system. Amino acids, charge ladders of positively and negatively charged proteins, and DNA fragments were separated in aqueous solutions with this system with resolution comparable to that obtained using fused silica capillaries.
  • The mechanical properties of the rubber elastic polymer polydimethylsiloxane for sensor applications, J. C. Lötters et al. (1997)
    TitleThe mechanical properties of the rubber elastic polymer polydimethylsiloxane for sensor applications
    AuthorsJ. C. Lötters, W. Olthuis, P. H. Veltink, P. Bergveld
    PublicationJournal of Micromechanics and Microengineering
    DateSept 1997
    AbstractPolydimethylsiloxane (PDMS) is a commercially available physically and chemically stable silicone rubber. It has a unique flexibility with a shear elastic modulus due to one of the lowest glass transition temperatures of any polymer . Further properties of PDMS are a low change in the shear elastic modulus versus temperature , virtually no change in G versus frequency and a high compressibility. Because of its clean room processability, its low curing temperature, its high flexibility, the possibility to change its functional groups and the very low drift of its properties with time and temperature, PDMS is very well suited for micromachined mechanical and chemical sensors, such as accelerometers (as the spring material) and ISFETs (as the ion selective membrane). It can also be used as an adhesive in wafer bonding, as a cover material in tactile sensors and as the mechanical decoupling zone in sensor packagings.
  • A Highly Symmetrical Capacitive Triaxial Accelerometer, Joost Conrad Lötters (1997)
    TitleA Highly Symmetrical Capacitive Triaxial Accelerometer
    AuthorJoost Conrad Lötters
    DateAug 1997
  • Polydimethylsiloxane, a photocurable rubberelastic polymer used as spring material in micromechanical sensors, Joost Conrad Lötters et al. (1997)
    TitlePolydimethylsiloxane, a photocurable rubberelastic polymer used as spring material in micromechanical sensors
    AuthorsJoost Conrad Lötters, Wouter Olthuis, Peter H. Veltink, Piet Bergveld
    PublicationMicrosystem Technologies
    DateFebruary 22, 1997
    AbstractPolydimethylsiloxane (PDMS) is a commercially available physically and chemically stable photocurable silicone rubber which has a unique flexibility (G곚rkPa) at room temperature. Further properties of PDMS are a low elasticity change versus temperature (1.1 kPa/°C), no elasticity change versus frequency and a high compressibility. PDMS is an interesting polymer to be used as spring material in micromechanical sensors such as accelerometers. The spring constant of the PDMS structures was theoretically calculated and measurements were done on accelerometers with PDMS springs to validate the theory. The measured and calculated spring constants showed a good correspondence, so the measurement results showed that the PDMS structures can successfully be used as mechanical springs.
  • Fundamentals of microfabrication, M. Madou (1997)
    TitleFundamentals of microfabrication
    AuthorM. Madou
    PublisherCRC Press
    AbstractMEMS technology and applications have grown at a tremendous pace, while structural dimensions have grown smaller and smaller, reaching down even to the molecular level. With this movement have come new types of applications and rapid advances in the technologies and techniques needed to fabricate the increasingly miniature devices that are literally changing our world. A bestseller in its first edition, Fundamentals of Microfabrication, Second Edition reflects the many developments in methods, materials, and applications that have emerged recently. Renowned author Marc Madou has added exercise sets to each chapter, thus answering the need for a textbook in this field. Fundamentals of Microfabrication, Second Edition offers unique, in-depth coverage of the science of miniaturization, its methods, and materials. From the fundamentals of lithography through bonding and packaging to quantum structures and molecular engineering, it provides the background, tools, and directions you need to confidently choose fabrication methods and materials for a particular miniaturization problem.
  • Polydimethylsiloxane as an elastic material applied in a capacitive accelerometer, Joost Conrad Lötters et al. (1996)
    TitlePolydimethylsiloxane as an elastic material applied in a capacitive accelerometer
    AuthorsJoost Conrad Lötters, Wouter Olthuis, Peter H. Veltink, Piet Bergveld
    PublicationJournal of Micromechanics and Microengineering
    DateMarch 1996
    AbstractPolydimethylsiloxane is a silicone rubber. It has a unique flexibility, resulting in one of the lowest glass-transition temperatures of any polymer. Furthermore, it shows a low elasticity change versus temperature, a high thermal stability, chemical inertness, dielectric stability, shear stability and high compressibility. Because of its high flexibility and the very low drift of its properties with time and temperature, polydimethylsiloxane could be well suited for mechanical sensors, such as accelerometers. A novel capacitive accelerometer with polydimethylsiloxane layers as springs has been realized. The obtained measurement results are promising and show a good correspondence with the theoretical values.
  • Series of AZ-compatible negative photoresists, Anya Voigt et al. (1995)
    TitleSeries of AZ-compatible negative photoresists
    AuthorsAnya Voigt, Gabi Gruetzner, E. Sauer, S. Helm, T. Harder, Simone Fehlberg, Juergen Bendig
    DateJune 09, 1995
    Conference NameAdvances in Resist Technology and Processing XII
    PlaceSanta Clara, CA, USA
  • Information About High Technology Silicone Materials, Dow Corning Corporation (1991)
    TitleInformation About High Technology Silicone Materials
    AuthorDow Corning Corporation