Fabrication Of 3D Microstructures Research Articles

Ultrathin and Deformable Graphene Etch Mask for Fabrication of 3D Microstructures.

Three-dimensional (3D) microfabrication techniques play a crucial role across various research fields. These techniques enable the creation of functional 3D structures on the microscale, unlocking possibilities for diverse applications. However, conventional fabrication methods have limits in producing complex 3D structures, which require numerous fabrication steps that increase the costs. Graphene is an atomically thin material known for its deformability and impermeability to small gases and molecules, including reactive gases like XeF2. These features make graphene a potential candidate as an etch mask for 3D microfabrication. Here, we report the fabrication of various 3D microstructures using graphene etch masks directly grown and patterned on a Si substrate. The patterned graphene deforms and wraps the etched structures, allowing for the fabrication of complicated 3D microstructures, such as mushroom-like and step-like microstructures. As a practical demonstration of the graphene etch mask, we fabricate an omniphobic surface of reentrant 3D structures on a Si substrate. Our work provides a method for fabricating complex 3D microstructures using a graphene etch mask, contributing to advancements in etching and fabrication processes.

Fabrication of 3D microstructures in glass by direct writing electrochemical discharge machining

ABSTRACT The formation of 3D copper-filled microstructures in glass using direct writing electrochemical discharge machining (ECDM) and electrodeposition techniques is presented. Single-row stainless steel tool electrodes having tip sizes of 150 µm were made by wire electrodischarge machining (W-EDM). Tool wear mechanism and the tip size correction of the worn-out tools were investigated. Significant tool wear was observed after 5 ECDM repetitions of the tool electrodes involving drilling and milling operations. Due to the high temperature generated in the ECDM process, there is significant erosion in the tool electrodes, and the tip heights of the electrodes became non-uniform. Thus, the single-row tool electrode became non-reusable in the ECDM process. Therefore, the electrochemical dissolution (ECD) method was used to correct the tip dimension and make the tool reusable for the ECDM process. After the ECD correction, the obtained tip size was close to the original size of 150 µm with <5% inter-tip size variation. Up to two-cycle of ECDM and ECD size correction was performed; thus, enhanced reusability of the single-row tool electrodes was demonstrated. The 3D structures were metallized using the copper electroplating method. DC measurement of the microstructures showed good electrical connectivity with an ohmic nature.

Fabrication of 3D microstructures for flexible pressure sensors based on direct-writing printing

Microstructure plays an important role in improving the performance of flexible sensors. Changing the shape of the dielectric layer microstructure is an effective countermeasure to promote the sensitivity of capacitive sensors. Nevertheless, traditional microstructure fabrication methods have high manufacturing costs, cumbersome manufacturing processes, and single structure manufacturing, which restrict the development of flexible sensors. In this work, electro-hydro-dynamic (EHD) printing method and aerosol jet (AJ) printing method were applied to fabricate 3D microstructures, in a manner of printing the same pattern in multiple layers. The height and morphology of 3D microstructures, under different printing parameters, were compared by changing the number of printing layers and printing speed. Additionally, the printing effects of the two printing methods were compared. The results demonstrated that various shapes and highly controllable 3D microstructures could be fabricated by both methods. The EHD printing method had higher manufacturing precision, whereas the AJ printing method had higher stacking efficiency. The height and morphology of 3D microstructures could be effectively controlled by changing the number of printed layers and the printing speed of the microstructures. It is indicated that the EHD printing method and the AJ printing method both have great potential in the fabrication of 3D microstructures and that both methods had their own advantages.

Compatibility of Popular Three-Dimensional Printed Microfluidics Materials with In Vitro Enzymatic Reactions.

3D printed microfluidics offer several advantages over conventional planar microfabrication techniques including fabrication of 3D microstructures, rapid prototyping, and inertness. While 3D printed materials have been studied for their biocompatibility in cell and tissue culture applications, their compatibility for in vitro biochemistry and molecular biology has not been systematically investigated. Here, we evaluate the compatibility of several common enzymatic reactions in the context of 3D-printed microfluidics: (1) polymerase chain reaction (PCR), (2) T7 in vitro transcription, (3) mammalian in vitro translation, and (4) reverse transcription. Surprisingly, all the materials tested significantly inhibit one or more of these in vitro enzymatic reactions. Inclusion of BSA mitigates only some of these inhibitory effects. Overall, inhibition appears to be due to a combination of the surface properties of the resins as well as soluble components (leachate) originating in the matrix.

Collagen/Chitosan Functionalization of Complex 3D Structures Fabricated by Laser Direct Writing via Two-Photon Polymerization for Enhanced Osteogenesis.

The fabrication of 3D microstructures is under continuous development for engineering bone substitutes. Collagen/chitosan (Col/CT) blends emerge as biomaterials that meet the mechanical and biological requirements associated with bone tissue. In this work, we optimize the osteogenic effect of 3D microstructures by their functionalization with Col/CT blends with different blending ratios. The structures were fabricated by laser direct writing via two-photons polymerization of IP-L780 photopolymer. They comprised of hexagonal and ellipsoidal units 80 µm in length, 40 µm in width and 14 µm height, separated by 20 µm pillars. Structures’ functionalization was achieved via dip coating in Col/CT blends with specific blending ratios. The osteogenic role of Col/CT functionalization of the 3D structures was confirmed by biological assays concerning the expression of alkaline phosphatase (ALP) and osteocalcin secretion as osteogenic markers and Alizarin Red (AR) as dye for mineral deposits in osteoblast-like cells seeded on the structures. The structures having ellipsoidal units showed the best results, but the trends were similar for both ellipsoidal and hexagonal units. The strongest osteogenic effect was obtained for Col/CT blending ratio of 20/80, as demonstrated by the highest ALP activity, osteocalcin secretion and AR staining intensity in the seeded cells compared to all the other samples.

A compact LED-based projection microstereolithography for producing 3D microstructures

Projection microstereolithography (PµSL) is a promising additive manufacturing technique due to its low cost, accuracy, speed, and also the diversity of the materials that it can use. Recently it has shown great potentials in various applications such as microfluidics, tissue engineering, micro-optics, biomedical microdevices, and so on. However, studies on PµSL are still ongoing in terms of the quality and accuracy of the construction process, which particularly affect the fabrication of complex 3D microstructures and make it attractive enough to be considered for commercial applications. In this paper, a compact LED-based PµSL 3D printer for the fabrication of 3D microstructures was developed, and the effective parameters that influence the quality of construction were thoroughly investigated and optimized. Accordingly, a customized optical system, including illumination optics and projection optics, was designed using optical engineering principles. This custom 3D printer was proposed for the PµSL process, which besides improving the quality of construction, led to the reduction of the size of the device, its cost-effectiveness, and the repeatability of its performance. To demonstrate the performance of the fabricated device, a variety of complex 3D microstructures such as porous, hollow, helical, and self-support microstructures were constructed. In addition, the repeatability of the device was assessed by fabricating microstructure arrays. The device performance showed that the lateral accuracy of printing was better than 5 μm, and the smallest thickness of the printed layer was 1 μm. Moreover, the maximum printable size of the device was 6.4 mm × 4 mm × 40 mm.

Two in One: Light as a Tool for 3D Printing and Erasing at the Microscale.

The ability to selectively remove sections from 3D-printed structures with high resolution remains a current challenge in 3D laser lithography. A novel photoresist is introduced to enable the additive fabrication of 3D microstructures at one wavelength and subsequent spatially controlled cleavage of the printed resist at another wavelength. The photoresist is composed of a difunctional acrylate cross-linker containing a photolabile o-nitrobenzyl ether moiety. 3D microstructures are written by photoinduced radical polymerization of acrylates using Ivocerin as photoinitiator upon exposure to 900 nm laser light. Subsequent scanning using a laser at 700 nm wavelength allows for the selective removal of the resist by photocleaving the o-nitrobenzyl group. Both steps rely on two-photon absorption. The fabricated and erased features are imaged using scanning electron microscopy (SEM) and laser scanning microscopy (LSM). In addition, a single wire bond is successfully eliminated from an array, proving the possibility of complete or partial removal of structures on demand.

Fabrication of 3D microstructures using grayscale lithography

Abstract Following the demand for three-dimensional (3D) micromachined structures, additive and subtractive processes were developed for fabrication of real 3D shapes in metals, alloys and monocrystalline Si (c-Si). As a primary structuring step for well-defined 3D structuring of the photoresist, grayscale lithography by laser direct writing was used. For additive fabrication of 3D microstructures, structured photoresist was used as molds. They were sputtered and subsequently electroplated by a metal (Cu) and an alloy (NiCo). The derived electroplated structures were demolded from the photoresist using an organic stripper. These metal structures are satisfactory replicas of the photoresist pattern. For subtractive pattern transfer of 3D structures into c-Si, reactive ion etching (RIE) was used to transfer the 3D photoresist structure into c-Si with 1:1 pattern transferability. The process parameters of RIE were optimized to obtain a selectivity of 1 and an anisotropy factor close to 1. Whereas conventional X-ray lithography (LIGA) and nanoimprint lithography result in 2.5D patterns, these techniques allow the fabrication of almost any arbitrary 3D shapes with high accuracy. In many cases, 3D structures (‘free forms’) are required, e.g. for molding of optical components such as spheres (or aspheres), channels for lab-on-a-chip and pillars for biological applications. Moreover, 3D structures on Si could be used as optical gratings and sensors.

Micro-EDM by using laminated 3D microelectrodes with deionized water containing B4C powder

The applicability of micro-electrical discharge machining (micro-EDM) using laminated 3D microelectrodes to eliminate defects such as numerous micro-stripes that are prone to appear on the sidewalls of microstructures manufactured via micro-electrochemical machining (micro-ECM) was examined. The study proposes the fabrication of 3D microstructures with laminated 3D microelectrodes through micro-EDM with deionized water containing B4C powder having a particle size of 1 μm. First, the effect of different machining voltages, B4C concentrations, and microelectrode back-off distances on the unilateral gap was investigated. The results indicated that a machining voltage of 100 V, a B4C concentration of 3 g/L, and a microelectrode back-off distance of 200 μm resulted in a 69 μm unilateral gap of the 3D microstructures. Given the effect of micro-EDM and that B4C is a semiconductor, the plasma discharge channels were enlarged, and the material removal was uniform. This significantly improved the machining efficiency. Furthermore, the polishing of B4C on electrode surfaces and workpiece surfaces smoothly removed the processing attachments with dielectric and ensured efficient and stable machining. Based on the optimized process parameters and after 1.5 h, 3D microstructures with a depth of 800 μm with a square-shaped blind hole and with semicircular and rectangular islands were obtained, and the corresponding roughness (Ra) of the bottom surface was 0.389, 0.388, and 0.392 μm. However, the corresponding microelectrodes wear was low and approximately corresponded to 20, 15, and 15 μm.

Femtosecond Laser Direct Write Integration of Multi-Protein Patterns and 3D Microstructures into 3D Glass Microfluidic Devices

Microfluidic devices and biochips offer miniaturized laboratories for the separation, reaction, and analysis of biochemical materials with high sensitivity and low reagent consumption. The integration of functional or biomimetic elements further functionalizes microfluidic devices for more complex biological studies. The recently proposed ship-in-a-bottle integration based on laser direct writing allows the construction of microcomponents made of photosensitive polymer inside closed microfluidic structures. Here, we expand this technology to integrate proteinaceous two-dimensional (2D) and three-dimensional (3D) microstructures with the aid of photo-induced cross-linking into glass microchannels. The concept is demonstrated with bovine serum albumin and enhanced green fluorescent protein, each mixed with photoinitiator (Sodium 4-[2-(4-Morpholino) benzoyl-2-dimethylamino] butylbenzenesulfonate). Unlike the polymer integration, fabrication over the entire channel cross-section is challenging. Two proteins are integrated into the same channel to demonstrate multi-protein patterning. Using 50% w/w glycerol solvent instead of 100% water achieves almost the same fabrication resolution for in-channel fabrication as on-surface fabrication due to the improved refractive index matching, enabling the fabrication of 3D microstructures. A glycerol-water solvent also reduces the risk of drying samples. We believe this technology can integrate diverse proteins to contribute to the versatility of microfluidics.

3D magnetic microstructures

We demonstrate the fabrication of 3D microstructures which display motion under the influence of a magnetic field. This is achieved by forming a coating of iron, known for its ferromagnetic properties, on 3D microstructures fabricated by Multiphoton Lithography. Pulsed Laser Deposition is the technique used to produce the iron coating. It is a simple and fast method that can be employed using a variety of materials. Movement of magnetic microstructures inside a liquid in response to a magnetic field has been observed.

On‐chip laser processing for the development of multifunctional microfluidic chips

AbstractIn the development of microfluidic chips, conventional 2D processing technologies contribute to the manufacturing of basic microchannel networks. Nevertheless, in the pursuit of versatile microfluidic chips, flexible integration of multifunctional components within a tiny chip is still challenging because a chip containing micro‐channels is a non‐flat substrate. Recently, on‐chip laser processing (OCLP) technology has emerged as an appealing alternative to achieve chip functionalization through in situ fabrication of 3D microstructures. Here, the recent development of OCLP‐enabled multifunctional microfluidic chips, including several accessible photochemical/photophysical schemes, and photosensitive materials permiting OCLP, is reviewed. To demonstrate the capability of OCLP technology, a series of typical micro‐components fabricated using OCLP are introduced. The prospects and current challenges of this field are discussed. image

Rapid fabrication of three-dimensional structures for dielectrophoretic sorting of lipid-containing organisms

In this work, we demonstrate a microfluidic particle sorter consisting of three-dimensional, conducting microposts. Our sorter uses dielectrophoresis (DEP) to sort high- and low-lipid phenotypes of the yeast Yarrowia lipolytica. Y. lipolytica is one of the many microorganisms being explored as a hydrocarbon source for biodiesel, Omega-3 additives, and other products derived from fatty acids. A rapid, non-destructive, lipid-based sorting tool would accelerate the commercialization of these products. Our device consists of an array of 105, 25 μm wide gold microposts that span the height of a 15 μm channel. This array generates an electric field in a microfluidic device that is uniform through the channel height, but has a custom-shaped non-uniformity in the horizontal directions. This is crucial in order to achieve continuous sorting using DEP, as it ensures all cells are exposed to the same conditions throughout the channel height. By using very low currents (100 μA), we are able to electroplate these post arrays in fewer than 15 min. This is an order of magnitude improvement over previous reports of electroplated microstructures. With an applied signal of 250 MHz, 2.6 Vpp in our device, we separate a heterogeneous population with a purity of 97.8% in the low-lipid stream and 71.4% in the high-lipid stream. The high-lipid stream purity can be improved by adjusting the spacing of the array. This unique protocol for the rapid fabrication of 3D microstructures has enabled the creation of a non-invasive sorting tool for genetically engineered, lipid-producing organisms. The ability to screen organisms based on lipid content will alleviate one of the major bottlenecks in commercialization of microbial biofuels.

Using low-contrast negative-tone PMMA at cryogenic temperatures for 3D electron beam lithography

We report on a 3D electron beam lithography (EBL) technique using polymethyl methacrylate (PMMA) in the negative-tone regime as a resist. First, we briefly demonstrate 3D EBL at room temperature. Then we concentrate on cryogenic temperatures where PMMA exhibits a low contrast, which allows for straightforward patterning of 3D nano- and microstructures. However, conventional EBL patterning at cryogenic temperatures is found to cause severe damage to the microstructures. Through an extensive study of lithography parameters, exposure techniques, and processing steps we deduce a hypothesis for the cryogenic PMMA’s structural evolution under electron beam irradiation that explains the damage. In accordance with this hypothesis, a two step lithography technique involving a wide-area pre-exposure dose slightly smaller than the onset dose is applied. It enables us to demonstrate a >95% process yield for the low-temperature fabrication of 3D microstructures.

Fabrication of 3D Microstructure by Localized Electrochemical Deposition with Image Feedback Distance Control and Five-Axis Motion Platform

The localized electrochemical deposition (LECD) process has been used to fabricate 3D microproducts. We combine the LECD process with a real-time 3D image feedback distance control system to improve the quality and conformational design complexity of 3D microproducts. Analyses of microproducts show that the main factor for designing complex 3D microproducts is the deposition direction angle that can be controlled in a 2D fabrication method. The deposition direction angle was the angle between the normal direction of the substrate surface and deposition direction. The normal direction of the substrate surface was determined 0°.We investigate two methods to improve the deposition direction angle in this study. The first method makes use of a new type of micro anode with asymmetric tip. By using this asymmetric micro anode, the deposition direction angle is found to range between −12.0° and 107.9°. This range is only to display the performance of the anode that proposed in this study. The second method is to redesign the moving mechanism and increase actuators and axes. By employing these two methods, we demonstrate high quality fabrication of two types of microstructures: helical springs with low pitch angle and inverted tripods.

青色半導体レーザーを用いた内部硬化型マイクロ光造形法の開発とナノインプリントへの応用

In this study, a versatile microstereolithography system using a low-cost blue diode laser was developed. This system enables to generate pinpoint photopolymerization at a focused spot inside a liquid photopolymer like two-photon microfabrication using a femtosecond pulsed laser. It can provide multiscale fabrication owing to the unique property of single-photon polymerization. A microstereolithograpy system using a 405 nm diode laser and galvano-scanner set was constructed. After investigating a suitable photopolymer by absorbance measurement, the fabrication resolution of this system was examined in experiments. In addition, three-dimensional (3D) microstructures including micro lattice models and movable microparts were successfully fabricated. Moreover, additive fabrication of 3D microstructures on patterned films produced by nanoimprinting was demonstrated.

Microfabrication of 3D metallic interconnects via direct laser writing and chemical metallization

We present a developed method based on direct laser writing (DLW) and chemical metallization (CM) for microfabrication of three-dimensional (3D) metallic structures. Such approach enables manufacturing of free-form electro-conductive interconnects which can be used in integrated electric circuits such as micro-opto-electro-mechanical systems (MOEMS). The proposed technique employing ultrafast high repetition rate lasers enables efficient fabrication of 3D microstructures on dielectric as well as conductive substrates. The produced polymer links out of organic-inorganic composite matrix after CM serve as interconnects of separate metallic contacts; their dimensions are: height 15 μm, width 5 μm, length 35–45 μm, and they could provide 300 nΩm resistivity measured in a macroscopic way. This proves the techniques potential for creating integrated 3D electric circuits at microscale.

Optimized SU-8 Processing for Low-Cost Microstructures Fabrication without Cleanroom Facilities

The study and optimization of epoxy-based negative photoresist (SU-8) microstructures through a low-cost process and without the need for cleanroom facility is presented in this paper. It is demonstrated that the Ultraviolet Rays (UV) exposure equipment, commonly used in the Printed Circuit Board (PCB) industry, can replace the more expensive and less available equipment, as the Mask Aligner that has been used in the last 15 years for SU-8 patterning. Moreover, high transparency masks, printed in a photomask, are used, instead of expensive chromium masks. The fabrication of well-defined SU-8 microstructures with aspect ratios more than 20 is successfully demonstrated with those facilities. The viability of using the gray-scale technology in the photomasks for the fabrication of 3D microstructures is also reported. Moreover, SU-8 microstructures for different applications are shown throughout the paper.

Polydimethyl siloxane wet etching for three dimensional fabrication of microneedle array and high-aspect-ratio micropillars.

Among various transdermal drug delivery (TDD) approaches, utilizing the microneedles (MNs) not only can penetrate the skin but also deliver the drug with reduced tissue damage, reduced pain, and no bleeding. However, the MNs with larger height are required to overcome the skin barrier for effective TDD. Unlike 2D patterning, etching polydimethyl siloxane (PDMS) micropillars for fabrication of 3D microstructures is presented. The PDMS micropillars were first constructed by casting PDMS on the computer numerical control-machined cylindrical microwells, which then went through etching process to obtain the MNs for subsequent fabrication of polymer MNs or high aspect ratio micropillars.

Fabrication of 3D Micro Structure by Dual Diffuser Lithography

Recently, products that a have 3-dimensional(3D) micro structure have been in wide use. To fabricate these 3D micro structures, several methods, such as stereo lithography, reflow process, and diffuser lithography, have been used. However, these methods are either very complicated, have limitations in terms of patterns dimensions or need expensive components. To overcome these limitations, we fabricated various 3D micro structures in one step using a pair of diffusers that diffract the incident beam of UV light at wide angles. In the experiment, we used positive photoresist to coat the Si substrate. A pair of diffusers(ground glass diffuser, opal glass diffuser) with Gaussian and Lambertian scattering was placed above the photomask in the passage of UV light in the photolithography equipment. The incident rays of UV light diffracted twice at wider angles while passing through the diffusers. After exposure, the photoresist was developed fabricating the desired 3D micro structure. These micro structures were analyzed using FE-SEM and 3D-profiler data. As a result, this dual diffuser lithography(DDL) technique enabled us to fabricate various microstructures with different dimensions by just changing the combination of diffusers, making this technology an efficient alternative to other complex techniques.