Fabrication of complex multilevel microchannels in PDMS by using three-dimensional photoresist masters

This 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.     

Applying magnetic soft mold imprint technology with ultraviolet light‐emitting‐diode array on the fabrication of microlens arrays

This study proposed a novel technology, which uses exposed technology with ultraviolet light‐emitting‐diode (UV‐LED) arrays and the polydimethylsiloxane (PDMS) magnetic flexible soft mold imprint technology, to develop exposed equipments with UV‐LED arrays. This study used magnetic soft mold imprint technology to replicate the structure of microlens, providing a more effective alternative for imprint technology and application. The measurement results showed that PDMS with magnetic iron powder can precisely cast mold to replicate the structures of microlens. Electromagnetic plates were used to control even imprinting with magnetic force, in order to fill the mold of micro‐structure of the photo‐resist. Magnetic iron powder was added to PDMS to produce composite material, which can effectively avoid the transformation of pure PDMS during soft mold imprinting, and increase mechanical strength. Magnetic PDMS soft mold is easy to make, and the casting time is short, so that costs can be effectively reduced. Also with advantages of less free energy on its surface, and unlikely to adhere to the photo‐resist during imprinting, it can be combined with electromagnetic plates evenly to control the magnetic soft mold. This imprinting technology is a big advantage to the production process of micro‐structures during imprinting. Copyright © 2009 John Wiley & Sons, Ltd.     

Fabrication of buried waveguide microstructure using gas‐assisted micro/nanoimprinting with soft mold

Due to the limitations on the choice of wavelengths available for light source, nanograde structures are facing technological bottlenecks and their method of preparation using current lithography and imaging technology is extremely costly. The idea is thus born to develop a nanopressuring and manufacturing technology, in order to further develop a low‐cost and more reliable technology to manufacture nanodevices in full scale. This study combines the characteristics of soft lithography, photo‐resist, and gas‐assisted pressuring, as well as studies the use of gas‐assisted pressuring and soft mold to emboss photo‐resist to manufacture optical waveguide devices, such that the nanopressuring technology may be more mature. Study results show that polydimethylsiloxane (PDMS) is able to accurately emboss and replicate nanograde buried waveguide structures, by using even pressure gas to achieve full contact with the surface of the substrate thus greatly increasing the effective pressuring area. Also, PDMS soft molds are easier to make with short embossing time to effectively reduce cost. Another advantage of combining gas‐assisted pressuring with PDMS soft molds in the manufacturing process is that PDMS soft molds possess low free energy on the surface and are difficult for resist to adhere. Copyright © 2007 John Wiley & Sons, Ltd.     

A novel electromagnetism‐assisted imprinting technology to replicate microstructures onto a large‐area curved surface using a flexible magnetic mold

Replication of microstructures from a mold onto a curved surface is difficult. The conformal contact between the mold and the substrate has to be ensured. The present study proposes an innovative mechanism, which employs an electromagnetic disk to provide magnetic force and a PDMS flexible mold with a layer compounded magnetic powder. This mechanism provides not only the gradual contact from center to edge to avoid air entrapment but also conformal contact between the mold and the substrate during the imprinting operation. A system based on this electromagnetic soft imprinting technology has been implemented, and imprinting to replicate microstructures from the mold onto a curved surface has been carried out. The results reveal that the PDMS magnetic mold and the electromagnetic disk‐controlled magnetic force can successfully perform the imprinting and accurately replicate the microstructures onto the large‐area, curved surface glass. The PDMS flexible magnetic mold incorporated with the magnetic disk can be employed to achieve the conformal contact between the mold and the substrate. In addition, due to the low surface free energy of the PDMS, the de‐molding without sticking can be easily accomplished. Copyright © 2008 John Wiley & Sons, Ltd.     

A facile approach to fabricate hierarchically structured poly(3‐hexylthiophene‐2,5‐diyl) films

Microstructured surfaces have great potentials to improve the performances and efficiency of optoelectronic devices. In this work, a simple robust approach based on surface instabilities was presented to fabricate poly(3‐hexylthiophene‐2,5‐diyl) (P3HT) films with ridge‐like/wrinkled composite microstructures. Namely, the hierarchically patterned films were prepared by spin coating the P3HT/tetrahydrofuran (THF) solution on a polydimethylsiloxane (PDMS) substrate to form stable ridge‐like structures, followed by solvent vapor swelling to create surface wrinkles with the orientation guided by the ridge‐like structures. During spin coating of the P3HT/THF solution, the ridge‐like structures were generated by the in‐situ template of the THF swelling‐induced creasing structures on the PDMS substrate. To our knowledge, it is the first report that the creasing structures are used as a recoverable template for patterning films. The crease‐templated ridge‐like structures were well modulated by the THF swelling time, the modulus of the PDMS substrate, the P3HT/THF solution concentration and the selective/blanket exposure of the PDMS substrate to O₂ plasma. UV–vis and fluorescence spectrometry measurements indicated that the light absorption and fluorescent emission were improved on the hierarchically patterned P3HT films, which can be utilized to enhance the efficiencies of organic solar cells. Furthermore, this simple versatile method based on the solvent swelling‐induced crease as the in‐situ recoverable template has been extended to pattern other spin‐coated films with different compositions. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 928–939     

Development and research for applying innovative magnetic soft mold imprinting techniques in microstructure component manufacturing

The present study employs an innovative technique, which uses PDMS soft mold, blended with magnetic powder as the transmission and imprinting methods, and integrates features from soft micromolding PMMA, an electro‐magnetically controlled, well‐proportioned, pressing technique in order to study how to create microlens arrays through a magnetic soft mold imprinting resist technique. Thus, it renders nanometer imprinting applications, and its technology, more developed and mature. The research findings revealed that, PDMS, blended with magnetic powder, can accurately recast and duplicate nanometer microstructures. Under well‐proportioned magnetic pressing, controlled by an electro‐magnetic disk, it can effectively fill and shape resist microstructures. The composite material of PDMS, with added magnetic iron powder, can effectively improve mechanical strength properties of pure PDMS soft mold, which is easily transformed for imprinting. Meanwhile, owing to the unique features of PDMS soft mold, conformal contact with the base material is possible; therefore, the effective imprinting area and the duplicated representation are significantly improved. In addition, as magnetic PDMS soft mold is easily produced and fast in recasting, the costs can be effectively reduced. In addition, due to features such as low surface free energy and a tendency not to stick to resist in imprinting, the soft mold is evenly controlled by the electro‐magnetic disk for imprinting duplication, highlighting the advantages of microstructure imprinting procedures. Copyright © 2008 John Wiley & Sons, Ltd.     

The application of elastic auxiliary air bag imprinting technology to the development of linear gradient micro‐structure replication processes

This study proposed an innovative imprinting process technology using an elastic auxiliary air bag imprinting mechanism, combined with poly(dimethylsiloxane) (PDMS) soft mold and UV–LED array photocuring equipment, to evenly imprint and reproduce a micro‐lens mold into a gradient micro‐lens structure in order to achieve linear gradient in micro‐structures. The structure defined by the proposed process technology is more continuous and smoother than that of the current semi‐conductor gray scale photomasking process technology. The process is simpler, faster, and less expensive and is a more effective option for satisfying the formation requirements of different structural heights. This study used pressure‐sensitive film to test and discuss gradient imprint force distribution. The test results suggested that different spring constants led to tilt impressions, which caused the PDMS soft mold to contact with the substrate surface at different pressures. The color depth distribution of the pressure‐sensitive film testing results indicated that the spring constant and pressure distribution were somewhat correlated. Hence, the height of structural formation can be controlled by different spring constants. Finally, SEM and surface profiler measurements suggested that different spring constants can result in different tilt degrees of the imprinting platform of air bag imprinting applications for the imprinting and reproduction of smooth, continuous micro‐lens array structures of different heights. Copyright © 2012 John Wiley & Sons, Ltd.     

A study on the innovative microlens projection lithography applied to the production of microstructures

Microlens projection lithography is a kind of non‐contact projection lithography that uses microlens array components as the projection lenses to produce a large area of microstructural array patterns on photoresisting film. This technology requires partial masking of light on the non‐lens portion of the microlens array, and the conventional approach is through an aligned exposure followed by the plating process that would require accurate positioning equipment, so it is naturally time‐consuming as well as costly in terms of the entire production process. This study applies an innovative technology in the production process that uses a microcircular‐hole array to penetrate a stainless‐steel substrate as the mold, and in collaboration with gas‐assisted thermal pressuring production process that utilizes surface tension of the plastic film to fabricate the hemisphere‐shaped plastic microlens array that is capable of masking light as the projection lens. With such a lens, in collaboration with optic expansion film, Fresnel lens, and millimeter‐grade single‐pattern photomasks, the microlens array projection lithographical optical system is constructed. Using regular millimeter‐grade photomasks, a micrometer‐grade array pattern is successfully fabricated on the photoresist layer through the process of projection exposure and development using such a microlens array projection lithographical optical system. Copyright © 2007 John Wiley & Sons, Ltd.     

Hydrophobic‐hydrophilic monolithic dual‐phase layer for two‐dimensional thin‐layer chromatography coupled with surface‐enhanced Raman spectroscopy detection

Hydrophobic‐hydrophilic monolithic dual‐phase plates have been prepared by a two‐step polymerization method for two‐dimensional thin‐layer chromatography of low‐molecular‐weight compounds, namely, several dyes. The thin 200 μm poly(glycidyl methacrylate‐co‐ethylene dimethacrylate) layers attached to microscope glass plates were prepared using a UV‐initiated polymerization method within a simple glass mold. After cutting and cleaning the specific area of the layer, the reassembled mold was filled with a polymerization mixture of butyl methacrylate and ethylene dimethacrylate and subsequently irradiated with UV light. During the second polymerization process, the former layer was protected from the UV light with a UV mask. After extracting the porogens and hydrolyzing the poly(glycidyl methacrylate‐co‐ethylene dimethacrylate) area, these two‐dimensional layers were used to separate a mixture of dyes with great difference in their polarity using reversed‐phase chromatography mode within the hydrophobic layer and then hydrophilic interaction chromatography mode along the hydrophilic area. In the latter dimension only the specific spot was developed further. Detection of the separated dyes could be achieved with surface‐enhanced Raman spectroscopy.     

A Simple Method for Fabricating Patterned Curvilinear Microstructures in Poly(dimethylsiloxane) by Selective Wetting

The fabrication of patterned microstructures in poly(dimethylsiloxane) (PDMS) is a prerequisite for soft lithography. Herein, curvilinear surface relief microstructures in PDMS are fabricated through a simple three‐stage approach combining microcontact printing (μCP), selective surface wetting/dewetting and replica molding (REM). First, using an original PDMS stamp (first‐generation stamp) with linear relief features, a chemical pattern on gold substrate is generated by μCP using hexadecanethiol (HDT) as an ink. Then, by a dip‐coating process, an ordered polyethylene glycol (PEG) polymer‐dot array forms on the HDT‐patterned gold substrate. Finally, based on a REM process, the PEG‐dot array on gold substrate is used to fabricate a second‐generation PDMS stamp with microcavity array, and the second‐generation PDMS stamp is used to generate third‐generation PDMS stamp with microbump array. These fabricated new‐generation stamps are utilized in μCP and in micromolding in capillaries (MIMIC), allowing the generation of surface micropatterns which cannot be obtained using the original PDMS stamp. The method will be useful in producing new‐generation PDMS stamps, especially for those who want to use soft lithography in their studies but have no access to the microfabrication facilities.     

Rapid fabrication of microchannels using microscale plasma activated templating (microPLAT) generated water molds

Poly(dimethylsiloxane) (PDMS) is a common material used in fabricating microfluidic devices. The predominant PDMS fabrication method, soft lithography, relies on photolithography for fabrication of micropatterned molds. In this technical note, we report an alternative molding technique using microscale PLasma Activated Templating (microPLAT). The use of photoresist in soft lithography is replaced by patterned water droplets created using microPLAT. When liquid PDMS encapsulates patterned water and then solidifies, the cavities occupied by water become structures such as microchannels. Using this method, device fabrication is less time consuming, more cost efficient and flexible, and ideal for rapid prototyping. An additional important feature of the water-molding process is that it yields structural profiles that are difficult to achieve using photolithography.     

Masterless soft lithography: patterning UV/ozone-induced adhesion on poly(dimethylsiloxane) surfaces

A novel microreactor-based photomask capable of effecting high resolution, large area patterning of UV/ozone (UVO) treatments of poly(dimethylsiloxane) (PDMS) surfaces is described. This tool forms the basis of two new soft lithographic patterning techniques that significantly extend the design rules of decal transfer lithography (DTL). The first technique, photodefined cohesive mechanical failure, fuses the design rules of photolithography with the contact-based adhesive transfer of PDMS in DTL. In a second powerful variation, the UVO masks described in this work enable a masterless soft lithographic patterning process. This latter method, UVO-patterned adhesive transfer, allows the direct transfer of PDMS-based polymer microstructures from a slab of polymer to silicon and other material surfaces. Both methods exploit the improved process qualities that result from the use of a deuterium discharge lamp to affect the UVO treatment to pattern complex, large area PDMS patterns with limiting feature sizes extending well below 1 microm (> or = 0.3 microm). The use of these structures as resists is demonstrated for the patterning of metal thin films. A time-of-flight secondary ion mass spectroscopy study of the process provides new insights into the mechanisms that contribute to the chemistry responsible for the interfacial adhesion of DTL transfers.     

High intensity light emitting diode array as an alternative exposure source for the fabrication of electrophoretic microfluidic devices

A commercially available array of light emitting diodes (LEDs), namely a UV Shark series LED high flux array, was evaluated as a light source for photolithographic patterning of SU-8 photoresist for the fabrication of templates suitable to make poly(dimethylsiloxane) (PDMS) microchips for electrophoresis. At a distance of 15 cm from the substrate, a relatively even intensity of 0.76+/-0.05 mW/cm(2) was obtained over an area sufficient for patterning a 10 cm (4 in.) silicon wafer. The exposure source was evaluated using a spiral mask design covering a 10 cm wafer. PDMS replicates of this template made in a 25 microm thick layer of SU-8 3025 showed little variation in width over the surface of the substrate, with a variation of 3.2% RSD (n=36) and a maximum range in widths of 7.8% of the mean channel width. The use of the optional metal reflector available with the LED array provided partial collimation of the light allowing near vertical structures to be produced across the entire wafer, something which was not possible without the reflector. SU-8 masters prepared using the LED array were compared to masters made using an alternative cheap lithographic source, namely a gel crosslinker. The SU-8 features were much narrower with the LED array than the crosslinker due to the multiple light sources in the crosslinker. A PDMS microchip made using a SU-8 template created using the Shark UV LED array was used for the electrophoretic separation of three anionic fluorescent dyes, with efficiencies up to 32,000 plates. Given that the LED array can be purchased and assembled for less than US$ 500, the Shark UV LED array is a promising alternative to more expensive lithographic light sources and will have significant appeal to many researchers wishing to undertake research in microfluidics around the world.     

Microfluidic chip fabrication using hot embossing and thermal bonding of COP

The application of silicon mold inserts by micro‐hot embossing molding has been explored in microfluidic chip fabrication. For the mold insert, this study employed an SU‐8 photoresist to coat the silicon wafer. Ultraviolet light was then used to expose the pattern on the SU‐8 photoresist surface. This study replicates the microstructure of the silicon mold insert by micro‐hot embossing molding. Different processing parameters (embossing temperature, embossing pressure, embossing time, and de‐molding temperature) for the cycle‐olefin polymer (COP) film of microfluidic chips are evaluated. The results showed that the most important parameter for replication of molded microfluidic chip is embossing temperature. De‐molding temperature is the most important parameter for surface roughness of the molded microfluidic chip. The microchannel is bonded with a cover by thermal bonding processing to form the sealed microfluidic chip. The bonding temperature is the most important factor in the bonding strength of the sealed microfluidic chip. Copyright © 2009 John Wiley & Sons, Ltd.     

Facile synthesis and responsive behavior of PDMS‐b‐PEG diblock copolymer brushes via photoinitiated “thiol‐ene” click reaction

We present herein a mild and rapid method to create diblock copolymer brushes on a silicon surface via photoinitiated “thiol‐ene” click reaction. The silicon surface was modified with 3‐mercaptopropyltrimethoxysilane (MPTMS) self‐assembled monolayer. Then, a mixture of divinyl‐terminated polydimethylsiloxane (PDMS) and photoinitiator was spin‐coated on the MPTMS surface and exposed to UV‐light. Thereafter, a mixture of thiol‐terminated polyethylene glycol (PEG) and photoinitiator were spin‐coated on the vinyl‐terminated PDMS‐treated surface, and the sequent photopolymerization was carried out under UV‐irradiation. The MPTMS, PDMS, and PEG layers were carefully identified by X‐ray photoelectron spectroscopy, atomic force microscopy, ellipsometry, and water contact angle measurements. The thickness of the polydimethylsiloxane‐block‐poly(ethylene glycol) (PDMS‐b‐PEG) diblock copolymer brush could be controlled by the irradiation time. The responsive behavior of diblock copolymer brushes treated in different solvents was also discussed. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Rapid prototyping of microstructures in polydimethylsiloxane (PDMS) by direct UV-lithography

Microstructuring of polydimethylsiloxane (PDMS) is a key step for many lab-on-a-chip (LOC) applications. In general, the structure is generated by casting the liquid prepolymer against a master. The production of the master in turn calls for special equipment and know how. Furthermore, a given master only allows the reproduction of the defined structure. We report on a simple, cheap and practical method to produce microstructures in already cured PDMS by direct UV-lithography followed by chemical development. Due to the available options during the lithographic process like multiple exposures, the method offers a high design flexibility granting easy access to complex and stepped structures. Furthermore, no master is needed and the use of pre-cured PDMS allows processing at ambient (light) conditions. Features down to approximately 5 μm and a depth of 10 μm can be realised. As a proof of principle, we demonstrate the feasibility of the process by applying the structures to various established soft lithography techniques.     

Synthesis and properties of UV curable polyvinylsilazane as a precursor for micro‐structuring

Photosensitive acrylated polyvinylsilazanes were prepared by reacting a diacrylate containing compound, 1,1‐bis (acryloyloxyethyl) ethyl isocyanate (BAEI), with polyvinylsilazane (PVSZ) and utilized as an inorganic photoresist for generating SiCN‐based ceramic microstructures. The acrylate‐modified polymers (m‐PVSZ) were characterized by ¹H‐NMR, ¹³C‐NMR and FT‐IR methods to determine the chemical reaction mechanism. Differential photo‐calorimeter and FT‐IR analysis were employed to examine its photosensitive properties. Line patterns were fabricated by a UV nano‐imprinting method; multi‐layered octagon structures were fabricated by a two‐photon absorption stereolithography process. The results indicate that m‐PVSZ is quite a novel inorganic photoresist for the fabrication of micro ceramic structures. Copyright © 2015 John Wiley & Sons, Ltd.     

Analysis of Dynamic and Thermodynamic Adsorption of Nanoparticles on Solid Surfaces by Dark‐Field Light Scattering Measurements

We have constructed a dark‐field light scattering microscope using a very low‐cost digital camera to investigate the adsorption of gold nanoparticles (AuNPs) on four different substrates at various pH values. The substrates used are glass, polycarbonate (PC), poly(dimethylsiloxane) (PDMS), and poly(methyl methacrylate) (PMMA). The coverage of AuNPs on hydrophobic substrates such as PDMS is greater than that on hydrophilic substrates like glass. The adsorption and aggregation of AuNPs on a particular substrate increased upon decreasing the pH (from 9.0 to 4.0). A greater coverage percentage of AuNPs, but less aggregation, occurs on glass treated with poly(diallyldimethylammonium) (PDDA) than on bare glass. The scattering intensity increases upon increasing the number of layers of adsorbed AuNPs on glass that was treated sequentially with AuNPs and PDDA. When compared to UV‐Vis absorption, dark‐field microscope provides greater sensitivity and qualitative surface information.     

Regular arrays of triangular‐microstructure formed on silicon (111) surface via ultrafast laser irradiation in KOH solution

The regular micrometer‐scale triangular arrays were formed using ultrafast femtosecond laser irradiation on (111) surface of silicon wafer immersed in KOH solution (0.1 g/ml). At low laser fluence, the resulting surface is covered by triangular pits microstructures, whereas at high laser fluence, the structures are transformed to multilayer‐triangular stacks‐microstructures. The number of triangular stacks layer increased as the laser fluence increased. The formation of triangle microstructure arrays depends on both silicon surface crystallographic orientation and the concentration of KOH solution. Either for lower KOH solution concentration (0.02 g/ml) or other silicon crystallographic orientation, triangle arrays cannot be obtained. We attribute the formation of triangular microstructure arrays to the laser‐assisted chemical etching process. Copyright © 2013 John Wiley & Sons, Ltd.     

可紫外光固化的聚乙烯基硅氮烷合成与表征

采用带丙烯酸酯基团的烯丙基溴化合物(4-溴丁烯酸乙酯)和聚乙烯基硅氮烷发生取代反应,实现了丙烯酸酯基团在聚乙烯基硅氮烷主链上的链接.采用质子核磁共振谱(1H-NMR)和二维质子核磁共振谱(2D-1H-1H-NMR)对分子结构进行了表征,采用光学差热分析仪(Photo-DSC)和傅立叶转换红外光谱仪(FT-IR)测试了改性高分子的光敏性能,用热重分析仪(TGA)分析了产物在高纯氮气氛围下的陶瓷收率.结果表明,通过分子改性,交联固化时间从改性前的20min减少到1min之内,功能化的聚乙烯基硅氮烷可以在光刻蚀工艺中作为负性光刻胶使用.