Master Fabrication Research Articles

Development platform for UV-NIL processes using polymer masters produced by laser ablation and photolithography

Ultraviolet nanoimprint lithography (UV-NIL) is a versatile and cost-effective technique for the fabrication of micro- and nanostructures by copying master patterns in a planar or a roll-to-roll process through curing of a liquid UV-sensitive precursor. For applications with a high pattern complexity, new UV-NIL process chains must be specified. Master fabrication is a challenging part of the development and often cannot be accomplished using a single master fabrication technique. Therefore, an approach combining different patterning fabrication techniques is developed here for polymer masters using laser direct writing and photolithography. The polymer masters produced in this way are molded into inverse silicone stamps that are used for roll-to-roll replication into an acrylate formulation. To fit the required roller size for large-area UV-NIL, several submasters with micrometer-sized dot and line gratings and prism arrays, which have been patterned by these different techniques, are assembled to final size of ∼200 × 600 mm2 with an absolute precision of better than 50 µm. The size of the submasters allows the use of standard laboratory equipment for patterning and direct writing, thus enabling the fabrication of micro- and even nanostructures when electron-beam writing is utilized. In this way, the effort, time, and costs for the fabrication of masters for UV-NIL processes are reduced, enabling further development for particular structures and applications. Using this approach, patterns fabricated with different laboratory tools are finally replicated by UV-NIL in an acrylate formulation, demonstrating the high quality of the whole process chain.

Self-assessment skills of undergraduate dental students in the preclinical course of complete removable prosthodontics at Tehran University of Medical Sciences.

This study evaluated the self-assessment skills of third-year dental students regarding their performance in complete removable prosthodontics (CRP) preclinical course. This cross-sectional study was conducted on all third-year dental students attending the International Dental College of Tehran University of Medical Sciences. The students were requested to self-assess their performance in primary impression making, custom tray fabrication, border moulding, final impression making, master cast fabrication, record-base fabrication and tooth arrangement in CRP preclinical course. The performance of dental students in each step was scored by themselves and their mentors. Data were analysed by the Mann-Whitney U, Pearson's correlation and t-tests (α = 0.05). Totally 25 male (55.6%) and 20 female (44.4%) dental students were evaluated. Significant differences were noted between male and female dental students in self-assessment scores regarding adequate extension of the custom tray (p = .027), the correct position of tray handle (p = .020), visibility of vestibular width and depth on the cast (p = .011), the coincidence of upper and lower midlines (p = .005) and correct orientation of maxillary and mandibular planes in the articulator (p = .036). The mean self-assessment score of female students was significantly higher than that of male students (p = .01). The scores given by the mentors were not significantly different for male and female students (p = .975). The difference between the self-assessment score of students and the mentor score was not significant (p = .067) either in males or in females (p > .05). Undergraduate dental students favourably self-assessed their performance in all steps of the preclinical course of CRP, comparable with their mentor assessment.

Robust fabrication of double-ring mushroom structure for reliable omniphobic surfaces

This paper presents a novel fabrication method for an unusual cylindrical double-ring mushroom structure (DMS). By using a conventional lithography process, a stable microstructure with omniphobic properties was constructed without additional chemical surface treatment with superior structural characteristics. The novelty of this DMS fabrication is demonstrated through footing effect errors that could occur during the silicon master fabrication process and demolding errors that could occur during the polymer replica process. The excellent omniphobic property of DMS is also demonstrated through a wettability test with comparisons of structures of similar dimension, and it exhibited strong resistance to contamination through comparative experiments of transmittance. As a result, thanks to low-cost fabrication method which does not require additional chemical treatment, our outstanding results with polymeric DMS surfaces are expected to affect various application fields.

Rapid Manufacturing of Multilayered Microfluidic Devices for Organ on a Chip Applications.

Microfabrication and Polydimethylsiloxane (PDMS) soft-lithography techniques became popular for microfluidic prototyping at the lab, but even after protocol optimization, fabrication is yet a long, laborious process and partly user-dependent. Furthermore, the time and money required for the master fabrication process, necessary at any design upgrade, is still elevated. Digital Manufacturing (DM) and Rapid-Prototyping (RP) for microfluidics applications arise as a solution to this and other limitations of photo and soft-lithography fabrication techniques. Particularly for this paper, we will focus on the use of subtractive DM techniques for Organ-on-a-Chip (OoC) applications. Main available thermoplastics for microfluidics are suggested as material choices for device fabrication. The aim of this review is to explore DM and RP technologies for fabrication of an OoC with an embedded membrane after the evaluation of the main limitations of PDMS soft-lithography strategy. Different material options are also reviewed, as well as various bonding strategies. Finally, a new functional OoC device is showed, defining protocols for its fabrication in Cyclic Olefin Polymer (COP) using two different RP technologies. Different cells are seeded in both sides of the membrane as a proof of concept to test the optical and fluidic properties of the device.

Versatile fabrication method for multiscale hierarchical structured polymer masters using a combination of photo- and nanoimprint lithography

We present a versatile and scalable method for the preparation of microfluidic channels with incorporated nano patterns. Since our approach is highly industrial driven, all used methods and materials are available in common micro-fabrication environment and are available in large quantities, respectively. In comparison to other fabrication methods capable of realizing multi-level patterns, we combine nanoimprint lithography with standard photolithography, and thereby overcome the problems of limited pattern dimensions as well as fabrication time, pathing the way for a new class of microfluidic devices. • High aspect ratio (AR = 11) fabrication of polymer masters using negative photoresists • Combinatorial approach for the fabrication of 2.5D scaffolds with micron and nano pattern • Combination of nanoimprint lithography and photolithography for fast prototyping • Optimized replication via soft-UV NIL using highly compatible resists and stamp materials

Design and Fabrication of Low-cost Microfluidic Channel for Biomedical Application

This paper presents the design, simulation and low-cost fabrication of microfluidic channel for biomedical application. Channel is fabricated using soft lithography technique. Printed Circuit Board (PCB) is used to make the master for the channel. Channel pattern is transferred on PCB plate using toner transfer technique followed by ferric chloride etching. Paper also discusses, the issues involved in PCB based master fabrication and their viable solutions. Glass is used as substrate material and the channel is made of Sylgard 184 Polydimethylsiloxane (PDMS). Channel is interfaced with a syringe pump to observe the fluid flow. To predict the behavior of the channel, FEM simulation is performed using COMSOL Multiphysics 5.2a. There is a good match between the theoretical, simulation and test results. Finally, to test the biocompatibility of the channel, genomic DNA is passed through the channel and gel electrophoresis analysis is performed.

Soft x-ray nanobeam formed by an ellipsoidal mirror

Ellipsoidal mirrors are promising optical devices for soft x-ray focusing. A fabrication process consisting of master fabrication and replication has been developed to produce ellipsoidal mirrors with wide apertures of approximately 10 mm. In the present study, the focusing performance of an ellipsoidal mirror was evaluated using soft x-rays in the soft x-ray beamline BL25SU-a of SPring-8. The focus sizes were measured at photon energies of 300, 400, and 500 eV. A quantitative figure error of the ellipsoidal mirror was also evaluated by analyzing the wavefield of the focused beam retrieved using ptychography. The figure error distributions measured at different photon energies agreed with each other at a root mean square level of 1 nm. The developed focusing system can be used for various types of microscopy, allowing the use of a wide range of x-ray energies.

Shear force measurement of actuated, gecko-inspired adhesion elements with hierarchical polydimethylsiloxane pattern

The transfer of systems from nature to technical schemes is still a challenge as the fabrication of such complex systems in a cost efficient way while keeping the intended technical functionality requires appropriate materials and fabrication techniques. Here the multi-scale hierarchy of the gecko foot was transferred into membrane-actuated gecko-inspired adhesion elements (AE) to study the adhesion to surfaces. Therefore, a three level hierarchical polydimethylsiloxane (PDMS) structure comprising a membrane for actuating and the micron-patterned AE were mould from a microtechnical fabricated master into PDMS by thermal and UV curing. The micron-patterned AE consist of dot or line micron patterns on top of cuboid posts with 15 µm height that representing the second hierarchical level. For master fabrication lithographic masking, wet and dry etching as well as SU8 3D lithography was applied.The adhesion of such AE on smooth, rough and chemically modified glass surfaces was measured by determining the shear force for several different AE designs and PDMS materials. A slip of the micron sized PDMS AEs at the adhesion test sample surface was measured. This slip of the PDMS elements being in contact to the surface can enhance the accepted shear force and the measured anisotropy of the shear force for linear AEs. The results found can contribute to the optimization of PDMS AE for technical surfaces with chemically and topographically inhomogeneous properties.

The fabrication of patterned metallic master by photolithography and electroplating technique for making PDMS-stamp as a tool for drug delivery system preparation

In this work, the micropatterned (Ni micropillars) masters were fabricated by combination of photolithography and electroplating technique. The polydimethylsiloxane (PDMS) stamps were successfully made by casting technique on micropatterned masters and used for further preparation of polymeric microchamber arrays film considered to be a drug delivery system. Micropatterned master fabrication is more precise technique, which is necessary for defects elimination.

Rapid Prototyping of Soft Lithography Masters for Microfluidic Devices Using Dry Film Photoresist in a Non-Cleanroom Setting.

Fabrication of microfluidic devices by soft lithography is by far the most popular approach due to simplicity and low cost. In this approach PDMS (polydimethylsiloxane) is cast on a photoresist master to generate replicas that are then sealed against glass slides using oxygen plasma. In this work, we demonstrated fabrication of soft photolithography masters using lamination of ADEX dry film as an alternative to the now classic SU-8 resist masters formed by spin coating. Advantages of using ADEX dry film include the easily-achievable uniform thickness without edge bead; simplicity of the process with significant time savings due to non-sticky nature of the film; and fewer health concerns due to less toxic developing solution and antimony-free composition. As we demonstrate, the process can be performed in a low-cost improvised fabrication room in ambient light, in place of a conventional yellow-light cleanroom environment. We believe this approach holds the promise of delivering state-of-the-art microfluidic techniques to the broad field of biomedical and pharmaceutical research.

Rapid fabrication and characterization of PDMS microfluidics device using printed conductive silver ink

Abstract Currently, new fabrication methods for rapid prototyping of microfluidic devices has bring attention among researchers from various fields. The main reason is the use of lithographic equipment in standard fabrication method for master fabrication require trained personnel and high cost disposable materials. In this paper, a new fabrication method via printed conductive silver ink is introduced in order to minimize the current fabrication process through elimination of the photolithography process. As a result, a usable, faster and cost effective prototyping process of a microfluidic based biosensor devices able to be produced. In this method, the conductive silver ink was used to create a master template contains microchannel onto glass-reinforced epoxy laminate sheets (FR-4). Then, Polydimethylsiloxane (PDMS) were used to replicate the structure. Next, the digital microscope was used to obtain images to demonstrate geometry fluidics structure with channel dimension up to 200 µm width. Moreover, a 3D profilometer was used to evaluate their thickness and roughness of the microfluidics structure. The stability test demonstrates the consistency of flow sequence inside the serpentine and separation channel.

Three-Dimensional Nanomolds Fabrication for Nanoimprint Lithography

Abstract Nanoimprint lithography is a fabrication method by applying nanomolds on resists to form inversed patterns. It can be utilized to fabricate high-resolution nanopatterns in a low cost and rapid fashion on both flat and curved surfaces. The fidelity of fabricated master nanopatterns and elastomer nanomolds are essential to the quality of the nanoimprinted features. Although two-dimensional nanoimprint lithography has been widely investigated, there are limited researches about three-dimensional master nanopatterns and nanomolds. Even less of them discussed the fidelity of entire procedures throughout the initial master fabrication to the final nanoimprinting. In this paper, we demonstrated the effectiveness of our approach, atomic force microscope (AFM) based ultrasonic vibration assisted nanomachining, in fabricating three-dimensional master nanopatterns with complex contours and continuously height changes. Nanomolds for nanoimprint lithography were fabricated subsequently based on the master nanopatterns with a positive draft, which is naturally generated from the AFM tip. We investigated the fidelity of the nanomachining results and the residual effect of reusing mater patterns. Besides, we demonstrated the 3D nanoimprinting capability of the solvent-assisted microcontact molding process, discovering the possibility of tuning the layer-thickness of imprinted 3D nanopatterns.

Fabrication of low-cost polydimethylsiloxane master from laminating foil for isotachophoresis separation on a chip

ABSTRACTThis article introduces use of laminating foils as the base for rapid polydimethylsiloxane master fabrication. The designs are punched directly to the foil structure with fabricated knife; therefore, the preparation time requires only a few minutes. This approach offers low-cost and variable possibility of master fabrication to produce microfluidic devices the size of dozens of microns. The resulting structures enable precise control of various device geometries, such as variable channel diameters and shapes in a single device. We describe the fabrication of microfluidic channels using these masters with polydimethylsiloxane polymer. The usability is demonstrated for the isotachophoretic separation of organic anionic dyes.

Multi-step Variable Height Photolithography for Valved Multilayer Microfluidic Devices.

Microfluidic systems have enabled powerful new approaches to high-throughput biochemical and biological analysis. However, there remains a barrier to entry for non-specialists who would benefit greatly from the ability to develop their own microfluidic devices to address research questions. Particularly lacking has been the open dissemination of protocols related to photolithography, a key step in the development of a replica mold for the manufacture of polydimethylsiloxane (PDMS) devices. While the fabrication of single height silicon masters has been explored extensively in literature, fabrication steps for more complicated photolithography features necessary for many interesting device functionalities (such as feature rounding to make valve structures, multi-height single-mold patterning, or high aspect ratio definition) are often not explicitly outlined. Here, we provide a complete protocol for making multilayer microfluidic devices with valves and complex multi-height geometries, tunable for any application. These fabrication procedures are presented in the context of a microfluidic hydrogel bead synthesizer and demonstrate the production of droplets containing polyethylene glycol (PEG diacrylate) and a photoinitiator that can be polymerized into solid beads. This protocol and accompanying discussion provide a foundation of design principles and fabrication methods that enables development of a wide variety of microfluidic devices. The details included here should allow non-specialists to design and fabricate novel devices, thereby bringing a host of recently developed technologies to their most exciting applications in biological laboratories.

A Rapid Prototyping Technique for Microfluidics with High Robustness and Flexibility.

In microfluidic device prototyping, master fabrication by traditional photolithography is expensive and time-consuming, especially when the design requires being repeatedly modified to achieve a satisfactory performance. By introducing a high-performance/cost-ratio laser to the traditional soft lithography, this paper describes a flexible and rapid prototyping technique for microfluidics. An ultraviolet (UV) laser directly writes on the photoresist without a photomask, which is suitable for master fabrication. By eliminating the constraints of fixed patterns in the traditional photomask when the masters are made, this prototyping technique gives designers/researchers the convenience to revise or modify their designs iteratively. A device fabricated by this method is tested for particle separation and demonstrates good properties. This technique provides a flexible and rapid solution to fabricating microfluidic devices for non-professionals at relatively low cost.

Plasmonic Colors: Toward Mass Production of Metasurfaces

Plasmonic metasurface coloration has attracted considerable attention in recent years due to its industrial potential. So far, demonstrations have been limited to small patterned areas fabricated using expensive techniques with limited scalability. This study elevates the technology beyond the common size and volume limitations of nanofabrication and demonstrates aluminum‐coated polymer‐based colored metasurfaces of square‐centimeter size by embossing, injection molding, roll‐to‐roll printing, and film insert molding. Different techniques are compared and the requirements and bottlenecks in terms of master fabrication, replication, metallization, and protection coating for large‐scale production of sub‐wavelength metasurfaces are discussed. Most notably, it is demonstrated that plasmonic metasurface colors are compatible with film insert molding. The results indicate a promising future for plasmonic colors as a viable alternative for decorating mass‐produced polymer parts.

Thermoplastic building blocks for the fabrication of microfluidic masters

This manuscript reports a building-block-based approach for the design and fabrication of masters that enables “ultra-rapid” prototyping of functional microfluidic systems.

Fabrication of nanometer electrodes by electro migration on an embedded metal pattern.

Electrodes with several tens nanometer gap are very important parts in the nano devices such as SETs (Single Electron Transistor), and quantum dots. However, fabricating nanometer electrode with the EBL (Electron Beam Lithography) process is too costly and time consuming to be commercially feasible. To overcome these disadvantages and to enable mass production, nano imprint lithography is applied to a master fabrication technique via EBL. In this paper, several tens nanometer gap electrodes are fabricated by EBL in order to characterize SET. The embedded metal pattern is made by the NIL (Nanoimprint Lithography) process, which is suggested for mass production. In order to fabricate without chemical process, the embedded metal process was executed with nanoimprint lithography. And the nanometer gap was made by electro migration process on flexible film substrate. That is, the electro migration process was executed on the embedded metal pattern to fabricate the nano gapped electrodes.

Fabrication and application of stainless steel stamps for the preparation of microfluidic devices

The use of an electrochemical polishing process to manufacture stainless steel stamps often gives rise to problems: there is a significant release of gas bubbles that can cause the photoresist mask to peel off. In this paper, a new procedure for the manufacture of stainless steel stamps is presented based on a combination of UV-lithography, gold electroplating, and electropolishing techniques. First, the pattern of the stamp is transferred to a photoresist layer by UV-lithography. The pattern in the photoresist is then filled in with a thin layer of gold formed by electroplating. The photoresist is then removed and the substrate etched in an electropolishing bath, with the gold layer serving as an etching mask. The steel stamps were repeatedly tested for the hot embossing of the polymethylmethacrylate substrate. The imprints were used for the preparation of functional microchips to test their functionality, the chips consisting of two polymethylmethacrylate plates: a plate with microchannels was embossed with a steel stamp, and a plate with inlet/outlet holes. The plates were joined by the thermal bonding method and the microchannels of the chip were then filled with a fluorescein solution to test whether the plates were properly bonded. The results indicate that this new procedure is suitable for the fabrication of flexible and durable masters for a roll-to-roll imprinting process.

Multi-Height Precision Alignment With Selectively Developed Alignment Marks

The alignment step in fabricating multi-height photoresist masters is a critical and time-consuming process. SU8 masters that combine very thin and thick layers can be difficult to align because of low contrast visibility. We increase visual contrast by selectively developing alignment marks to ease fabrication of masters with thick resist layers deposited on much thinner ones. In addition, we use a vernier calliper based alignment mark to achieve high precision alignment.