Surface Microfabrication Research Articles

Surface Microfabrication of Lactic Acid–Glycolic Acid Copolymers Using a Gas-Permeable Porous Mold

We attempted to perform surface microfabrication of the bioabsorbable material lactic acid–glycolic acid copolymer (LG-80) using a micro-imprint lithography technique with a gas-permeable porous mold at less than 5 °C. As a result, high-resolution surface micromachining with a height of 1.26 μm and a pitch of 2.97 μm was achieved using a convex sapphire mold with a height of 1.3 μm and a pitch of 3 μm. After processing, the LG-80 exhibited high water repellency, and FT-IR analysis of the surface showed no significant change in its chemical structure, confirming that the surface microfabrication was successful, while retaining the properties of the material. This demonstrated new possibilities for surface microfabrication technology for bioabsorbable materials, which are expected to be applied in the medical and life science fields in products such as surgical implants, tissue regeneration materials, and cell culture scaffold materials. In particular, the use of micro-imprint lithography enables low-cost and high-precision processing, which will be a major step toward the practical application of bioabsorbable materials.

Fiber laser irradiation in chemical solution for micro fabrication: Mechanisms and applications

The laser and electrochemical hybrid machining (LECM) could realize high-efficient and quality processing of difficult-to-cut materials and has become a research topic in microfabrication. However, it was difficult to ensure the stability and efficiency of laser transmission in chemical solutions, and an external voltage and auxiliary cathode should be added. In the present study, a novel fiber laser irradiation in chemical solution (LICS) has been proposed to process microstructures. The surface microstructures and chemical composition of the surfaces processed by LICS, laser irradiation in the ultrapure water, and electrochemical machining were compared. In LICS the materials were removed by laser processing and the following high-temperature gradient induced electrochemical dissolution. The high temperature gradient induced electrochemical dissolution could enhance the MRR and improve the surface quality. LICS can be regarded as a novel LECM process. The machining efficiency of LICS had been improved by 46.2 % compared with that laser irradiation in the ultrapure water, and the proportion of laser-induced electrochemical dissolution was 31.6 % in the LICS process. Further, the effects of laser power, chemical solution concentration, and optical fiber end movement control on the processing of micro grooves were explored, considering the dimension, MRR, and surface roughness. A front gap of smaller than 0.8 mm between the optical fiber end and workpiece was recommended during LICS. The repeated feeding of optical fiber was proposed to improve the depth-to-width ratio of the micro grooves fabricated by LICS. Finally, LICS was used to process microstructures with the controlled profiles on the nickel-based superalloy and titanium alloy workpieces without a recast layer, which holds great potential in surface microfabrication and texturing.

Experimental Research on the Aerodynamic Control by Microfabrication Surface Texture

Experimental Research on the Aerodynamic Control by Microfabrication Surface Texture

Micro-fabrication of textured surfaces using wire-mesh electrode in reverse µEDM

Micro-fabrication of textured surfaces using wire-mesh electrode in reverse µEDM

3D microfabrication by applying the laser-induced bubble method to the thermoset polymer PDMS using a conventional nanosecond laser.

We recently developed a microfabrication technique [microfabrication using laser-induced bubble (microFLIB)] and applied it to polydimethylsiloxane (PDMS), a thermoset polymer. The technique enabled the rapid fabrication of a microchannel on a PDMS substrate and selective metallization of the channel via subsequent plating; however, the technique was limited to surface microfabrication. Therefore, we explored the feasibility of three-dimensional (3D) microFLIB of PDMS using a nanosecond laser. In the experiment, a laser beam was focused inside pre-curing liquid PDMS and was scanned both perpendicular and parallel to the laser-beam axis to generate a 3D line of laser-induced bubbles. In the microFLIB processing, the shape of the created bubbles was retained in the pre-curing PDMS for more than 24 h; thus, the line of bubbles generated by the perpendicular laser scanning successfully produced a 3D hollow transverse microchannel inside the PDMS substrate after subsequent thermal curing. In addition, a through-hole with an aspect ratio greater than ∼200 was easily fabricated in the PDMS substrate by parallel laser scanning. The fabrication of a 3D microfluidic device comprising two open reservoirs in a PDMS substrate was also demonstrated for biochip applications.

Multi-Ion-Based Modelling and Experimental Investigations on Consistent and High-Throughput Generation of a Micro Cavity Array by Mask Electrolyte Jet Machining.

The controllability and consistency in the fabrication of micro-textures on large-scale remains a challenge for existing production processes. Mask electrolyte jet machining (MEJM) is an alternative to Jet-ECM for controllable and high-throughput surface microfabrication with more consistency of dimensional tolerances. This hybrid configuration combines the high-throughput of masked-ECM and the adjustable flow-field of jet-ECM. In this work, a duckbill jet nozzle was introduced to make MEJM more capable of batch micro-structuring. A multiphysics model was built to simulate the distribution of electrochemical reaction ions, the current density distribution, and the evolution of the shape of the machined cavity. Experimental investigations are presented showing the influence of the machining voltage and nozzle moving speed on the micro cavity. Several 35×35 micro cavity arrays with a diameter of 11.73-24.92 μm and depth of 7.24-15.86 μm are generated on 304 stainless steel.

Curvature-controlled delamination patterns of thin films on spherical substrates

SummaryPeriodic delamination patterns in multilayer structures have exhibited extensive applications in microelectronics and optics devices. However, delamination behaviors of a closed thin shell on spherical substrates are still elusive. Herein, a unique instability mechanism of buckle delamination in a closed thin film weakly bonded to spherical substrates is studied by experiments, simulations, and theoretical analyses. The system of an Al film depositing on polystyrene spheres subjected to thermal mismatch strain is used for demonstration. Unlike traditional phenomena of wrinkling and wrinkle-induced delamination under increasing misfit strain, the weak adhesion between the core and shell results in a periodic pattern of delaminated hexagonal dimples that emerges directly from the smooth sphere configuration, before which no wrinkling occurs. Both substrate curvature and interfacial adhesion are revealed to control the dimple size and delamination width. These findings open a new venue for manifesting new controllable features for surface microfabrication.

Microfabrication of re-entrant surface with hydrophobicity/oleophobicity for liquid foods

Re-entrant texturing may potentially improve the hydrophobicity and oleophobicity of a surface. The food industry requires a microfabrication method to keep surfaces clean without leaving a packaging residue for applications such as food bottles, food containers, and preservation bags. The goal of this study is thus to establish a microfabrication method for re-entrant texturing with spherical curvature to produce hydrophobic/oleophobic surfaces for liquid foods, such as soy sauce and canola oil. Samples with a spherical curvature are created from an ultra-violet-cure (UV-cure) resin and poly (tetrafluoroethylene) (PTFE) microbeads with diameters between 2.26 to 1,353 microns by spin coating on a glass substrate. The resin thickness, the mass and diameter of the microbeads, and the spin coater rotation speed are used as the microfabrication parameters. A side view of samples showing the spherical curvature reveals that a re-entrant texture indeed forms. Distilled water, soy sauce, and canola oil are dropped softly onto the re-entrant surface, however, the droplets cannot be placed stably. For appropriate microbead diameters, the apparent contact angles of soy sauce and canola oil showed 130.2 and 119.4 degrees, respectively. This facile fabrication method for re-entrant surfaces could prove useful for generating hydrophobic/oleophobic surfaces for Newtonian liquid foods.

Microfabrication of UV-transparent fluoropolymer using high-repetition femtosecond oscillator

Surface microfabrication of a UV-transparent fluoropolymer (CYTOP) was achieved using direct laser ablation with a femtosecond (fs) oscillator. The commercially available CYTOP is highly transparent and has a low refractive index comparable to that of water. Therefore, this polymer is a candidate biochip material for application in the field of tissue engineering. We have previously developed techniques for microfabrication of CYTOP using nanosecond and amplified fs laser ablation, both followed by wet etching and annealing. However, these techniques were not suitable for some industrial applications due to the generation of debris and cracks around the ablated areas, which called for prolonged etching during the fabrication process. To overcome these problems, we have attempted to directly ablate the surface of a CYTOP substrate using a high-repetition fs oscillator and compared the results with fabrication using an amplified fs laser at a low repetition rate. Consequently, ablation with the fs oscillator resulted in high-quality surface microfabrication of the CYTOP substrate. The fundamental characteristics of CYTOP microfabrication using the fs oscillator were investigated. We also demonstrate the fabrication of a transmission diffraction grating on CYTOP using the fs oscillator, and measure the diffraction efficiency of the grating using a 632 nm He–Ne laser.

Microfabrication of re-entrant surface with oleophobicity

Microfabrication of re-entrant surface with oleophobicity

Microfabrication of Re-entrant Surface with Hydrophobicity

Microfabrication of Re-entrant Surface with Hydrophobicity

Realization of Superhydrophobic Surfaces Based on Three-Dimensional Printing Technology

A superhydrophobic surface was successfully realized using fused deposition modeling-type three-dimensional (3D) printing technology. The low printing resolution (400 μm) and various printing angles from 0° to 90° were employed to print the mold for casting of polymer surfaces. The polymer surface cast from the mold exhibited waveform microstructures that had a tilting angle almost identical to the printing angle. The maximum average water contact angle (WCA) of fabricated polymer surfaces was 160°, which is much higher than that of flat (bare) polymer surfaces (up to 52.3% increase in the WCA). In particular, water droplets immediately rolled off along 8°-tilted surfaces, cast from the mold printed with printing angle of 70°. This demonstrated the superhydrophobic property. The result of this study shows the feasibility of a facile, rapid, inexpensive, and effective microfabrication of superhydrophobic surfaces using the current 3D printing technology.

Microfabrication of Low Cost Frequency Selective Surface for Terahertz Wave by Laser Ablation

A method of fabricating and characterizing terahertz frequency selective surface filters from a low-cost silver adhesive tape has been reported in this paper. The proposed filter was initially evaluated numerically using the method of moment’s simulation and verified experimentally by terahertz time-domain spectroscopy technique. The numerical results show that the cross aperture frequency selective surface has angle-resolved and polarization independent operation. The proposed silver adhesive tape and conventional copper-based frequency selective surface have been fabricated using a laser micromachining process. A 20 ns-pulsed laser operating at 1064 nm wavelength was used to create the desired structure by ablation mechanism in the copper film. The pattern ablated by the laser is a cross-shaped slit on copper and silver adhesive tape. The patterned structure was designed to resonate at 0.25 THz by the cross-arm structure. The fabricated structure shows the peak transmittance of 90% with a full-width half maximum of 48% with respect to the resonance. The adhesive tape based frequency selective surface provides similar transmission characteristics compared to a conventional frequency selective surface.

Etching-Assisted Ablation of the UV-Transparent Fluoropolymer CYTOP Using Various Laser Pulse Widths and Subsequent Microfluidic Applications.

This work demonstrated the surface microfabrication of the UV-transparent fluoropolymer CYTOP (perfluoro 1-butenyl vinyl ether), by etching-assisted ablation using lasers with different pulse widths. In previous studies, we developed a technique for CYTOP microfluidic fabrication using laser ablation followed by etching and annealing. However, this technique was not suitable for some industrial applications due to the requirement for prolonged etching of the irradiated areas. The present work developed a faster etching-assisted ablation method in which the laser ablation of CYTOP took place in fluorinated etching solvent and investigated into the fabrication mechanism of ablated craters obtained from various pulse width lasers. The mechanism study revealed that the efficient CYTOP microfabrication can be achieved with a longer pulse width laser using this technique. Therefore, the rapid, high-quality surface microfabrication of CYTOP was demonstrated using a conventional nanosecond laser. Additionally, Microfluidic systems were produced on a CYTOP substrate via the new etching-assisted laser ablation process followed by annealing within 1 h, which is faster than the prior work of the microfluidic chip fabrication. Subsequently, CYTOP and polydimethylsiloxane substrates were bonded to create a 3D microfluidic chip that allowed for a clear microscopic image of the fluid boundary.

Microfabrication of terahertz frequency-selective surface by short- and ultrashort laser ablation

This paper presents the method of fabricating a frequency-selective surface (FSS) filter for terahertz frequency by short- and ultrashort laser ablation process. The FSS consists of a capacitive screen made up of the copper metallic structure supported by a Teflon dielectric substrate. The dielectric properties of the Teflon substrate at terahertz frequencies were evaluated using THz-time-domain spectroscopy technique. The numerical simulation of the designed structure was performed using Computer Simulation Technology microwave studio software with unit cell configurations and the resonance was observed at 0.135 THz. The desired metallic microstructure was created in copper using an 8-ns solid-state Nd: YAG and 150 fs Ti:sapphire laser operating at the second harmonic wavelength of 532 and 800 nm, respectively. The proposed structure provides polarization-independent operation. The experimental verification of the fabricated FSS using femtosecond ablation process was done using THz-TDS technique, and it is observed that the measured data well match with the simulated result.

Surface Microfabrication of Conventional Glass Using Femtosecond Laser for Microfluidic Applications

Recently, a lot of attention has been paid to a single-cell analysis using microfluidic chips, since each cell is known to have several different characteristics. The microfluidic chip manipulates cells and performs high-speed and high-resolution analysis. In the meanwhile, femtosecond (fs) laser has become a versatile tool for the fabrication of microfluidic chips because the laser can modify internal volume solely at the focal area, resulting in three-dimensional (3D) microfabrication of glass materials. However, little research on surface microfabrication of materials using an fs laser has been conducted. Therefore, in this study, we demonstrate the surface microfabrication of a conventional glass slide using fs laser direct-writing for microfluidic applications. The fs laser modification, with successive wet etching using a diluted hydrofluoric (HF) acid solution, followed by annealing, results in rapid prototyping of microfluidics on a conventional glass slide for fluorescent microscopic cell analysis. Fundamental characteristics of the laser-irradiated regions in each experimental procedure were investigated. In addition, we developed a novel technique combining the fs laser direct-writing and the HF etching for high-speed and high-resolution microfabrication of the glass. After establishing the fs laser surface microfabrication technique, a 3D microfluidic chip was made by bonding the fabricated glass microfluidic chip with a polydimethylsiloxane (PDMS) polymer substrate for clear fluorescent microscopic observation in the microfluidics.

A novel multi-level IC-compatible surface microfabrication technology for MEMS with independently controlled lateral and vertical submicron transduction gaps

An above-IC compatible multi-level MEMS surface microfabrication technology based on a silicon carbide structural layer is presented. The fabrication process flow provides optimal electrostatic transduction by allowing the creation of independently controlled submicron vertical and lateral gaps without the need for high resolution lithography. Adopting silicon carbide as the structural material, the technology ensures material, chemical and thermal compatibility with modern semiconductor nodes, reporting the lowest peak processing temperature (i.e. 200 °C) of all comparable works. This makes this process ideally suited for integrating capacitive-based MEMS directly above standard CMOS substrates. Process flow design and optimization are presented in the context of bulk-mode disk resonators, devices that are shown to exhibit improved performance with respect to previous generation flexural beam resonators, and that represent relatively complex MEMS structures. The impact of impending improvements to the fabrication technology is discussed.

Stereolithography of perfluoropolyethers for the microfabrication of robust omniphobic surfaces

In this work, we provide a simple and straightforward method for the fabrication of stable highly hydrophobic and oleophobic surfaces by applying stereolithography (SL) to perfluoropolyethers (PFPEs). Inspired by the liquid repellency widely shown in nature, our approach enables to easily mimic the interplay between the chemistry and physics by microtexturing low surface tension PFPEs. To this end, UV-curable resins suitable for SL-processing were formulated by blending multifunctional (meth-)acrylates PFPEs oligomers with photoinitiator and visible dyes whose content was tuned to tailor resin SL sensitivities. Photocalorimetric studies were also performed to investigate the curing behavior of the different formulations upon SL light exposure. Being the first example of stereolithography applied to PFPEs, stereolithographic processability of new developed PFPEs photopolymer was compared with a standard photoresist taken as benchmark (DL260®). Optimized formulations were characterized by reduced laser penetration depth (<75μm) and small critical energies thus enabling for fast printing of micrometric structures. Arrays of cylindrical pillars (85μm diameter, 400μm height) characterized by varied pillars spacing (200÷350μm) were rapidly printed with high fidelity as attested by SEM examination. Contact angle measurements in static and dynamic conditions were performed to investigate the surface properties of textured samples using water and oil as the probing liquids. PFPEs liquid repellent performances were compared with those from DL260® textured surfaces arrayed by SL. High water contact angles coupled with low hysteresis asserted that high hydrophobic surfaces were successfully obtained and best-performing textured surfaces were also characterized by high oil repellency. Finally, this study demonstrated that omniphobic surfaces can be easily realized via a single-step, cost-effective, and time-saving process.

Biochip for Single Cell Analysis Using Laser Microfabrication1

We demonstrate laser microfabrication of transparent fluoric polymer using a conventional green laser. Fluoric polymers have unique characteristics such as high transparency, chemical resistance, and low refractive index and are expected to overcome many problems which conventional polymers have for biochip applications. We developed crack-free surface microfabrication of commercially available fluoric polymer commercially available fluoric polymer CYTOP (Asahi Glass Co., Ltd., Tokyo) using a conventional green laser. The laser ablation with successive wet etching by fluorine solution and annealing achieves high-quality microfluidics on the surface of the polymer substrate. In addition, we demonstrate the fabrication of a biochip with a three-dimensional fluid structure by bonding two pieces of CYTOP substrates for clear microscopic observation of swimming aquatic microorganism at the sidewall of the fluidics.

Microfabrication of the UV transparent polymer CYTOP using a conventional pulsed green laser

We report the surface microfabrication of CYTOP, an amorphous UV transparent fluoric polymer, using a conventional pulsed green laser. Fluorine-based polymers have unique characteristics, including high transparency from the deep-UV to the IR wavelengths, chemical stability and low refractive indices, and thus are expected to have a number of industrial applications. However, CYTOP and other fluoric polymers are generally very difficult to microfabricate. Therefore, we have developed a technique for the crack-free surface microfabrication of a CYTOP substrate based on ablation with a pulsed green laser followed by successive wet etching and annealing. In this work, the fundamental surface characteristics of the fabricated area were investigated. Following the surface microfabrication of CYTOP, a three-dimensional biochip was fabricated using a conventional bonding technique to demonstrate that a CYTOP biochip is superior to conventional transparent biochips with regard to the microscopic observation of cell motion.