Application of photo-etching of polytetrafluoroethylene induced by high energy synchrotron radiation to LIGA

Polytetrafluoroethylene (PTFE) microstructures’ processing characteristics using X-ray photo decomposition and desorption are studied in the highest energy region (2–12 keV). While the exposed surface states are seen melting and boiling from the remaining bubble structure of the irradiated surface, basic photochemistry of PTFE is also same as previous reports. Surface modification of PTFE from hydrophobic to hydrophilic was investigated in order to bond PTFE sheets to a brass substrate. Then, we have a successfully fabricated Ni microstructure by LIGA process using PTFE photo-etching using high energy X-ray. Proposed LIGA using SR-photo-etching of PTFE can simplify the total process, and it can ensure that dimensional errors remain small due to swelling in developer and electroplating bath.     

Direct bonding of PFTF sheets assisted by shynchrotron radiation induced surface modification

Characteristics of the microfabrication and modification of polytetrafluoroethylene (PTFE) using X-ray photo decomposition desorption and ablation are studied in the highest energy region (2 keV to over 12 keV). We have discussed that the PTFE polymer takes liquid state due to irradiation of high-energy photons with high-penetration depth, and this leads to the dominant decomposition, photo-induced ablation of PTFE and following generation of the volatile fragments including PTFE polymer itself. Furthermore, we found that melting point of the surface bulk layer of PTFE drastically decreased due to the irradiation of SR. The result of the differential thermal analysis of the SR-irradiated PTFE sheet shows the decay of the weight of PTFE sheet induced by thermal desorption starts at 155°C. This suggests that the apparent melting point of PTFE of which surface is modified by SR irradiation decreases drastically from original melting point. We finally successfully demonstrated that the two PTFE sheets could be bonded directly at low temperature less than 200°C without bonding reagent.     

Application of the inclined exposure and molding process to fabricate a micro beam-splitter with nanometer roughness

This paper successfully used inclined exposure technology to fabricate a wafer-level 3D micro cube beam splitter with a 45° optical grade surface (~1.4 mm thick). This research also tests the effect of solvent loss percentage of the SU-8 3035 polymer material (85.45 % solvent removal) to optimum surface roughness on the surface roughness of inclined surfaces. The smallest surface roughness achieved in the experiments using SU-8 3035 material with a thickness of 1.4 mm was less than 34 nm (400 × 400 μm area). And the reflective surface roughness of the molding cube beam-splitter is below 2 nm. The optical power of the fabricated cube beam splitter is about 60.55 and 39.44 % for transmission and reflection, respectively. This type of micro cube beam-splitter can be used as a key component in Pico-projectors, Interferometers, bio detection systems, data storage systems, and linear encoder optic systems. And this novel technology also has the characteristics of high throughput and wafer-level assembly.     

Immunoassay using poly-tetrafluoroethylene microstructure in organic solvent

This paper reports the first application of poly-tetrafluoroethylene (PTFE) microstructure, which fabricated by synchrotron radiation induced photo-evaporation process, to enzyme-linked immunosorbent assay. The advantages of PTFE microstructure for the development of lab-on-a-chip due to the extremely high-aspect ratio microstructure and chemical stability of PTFE is discussed. The results of immunoassay shows the successful detection of analyte (mouse IgG) with detection range with 0–100 ng/ml. This result suggests the successful immobilization of antibody (anti-mouse IgG goat antibody) onto the X-ray exposed surface of PTFE microstructure and successful demonstration of antigen–antibody reaction in the PTFE microstructure. We also demonstrated the detection of polychlorinated biphenyl (PCB). As the result of demonstration, we successfully detected PCB with ranging analyte concentration of 0.1–10 ng/ml.     

Resin micromachining by roller hot embossing

The roller hot embossing is an efficient process of manufacture in which patterns are continuously transcribed on film, etc. Recently, the application of the embossing roll to the manufacturing processes of micro parts is paid attention. In this paper, we examined the development of the embossing roll with patterns of micron level and we tried to make the embossing roll mold by using the LIGA process. In this study, instead of producing embossing patterns directly on the roll surface, we fabricated a flexible thin mold with micro-patterns, which was then wrapped onto a cylinder to form an embossing roll, and tested the soft-mold roller hot embossing method. First, by optimizing UV exposure conditions of UV lithography, we prepared a resist pattern of numerous dots with a diameter of 10 μm, a sag height of 8 μm and a pitch of 20 μm. By Ni-electroforming this pattern, a 50 μm-thick thin mold was successfully fabricated. The 50 μm-thick mold was then wrapped onto a cylinder to form an embossing roll. In the roller hot embossing process, the 10 μm-diameter dot shape was successfully replicated on PET sheets.     

Surface microfluidics fabricated by photopatternable superhydrophobic nanocomposite

Surface microfluidics can be of potential use in a variety of emerging applications, including biological and chemical analysis, cellular detection and manipulation, high-throughput pharmaceutical screening, and etc. In comparison with the conventional closed-channel microfluidic system, surface microfluidics shows the distinct advantages of simple construction, direct surface access, no cavitation or interphase obstruction, clear optical path, easy fluidic packaging, and device reusability. In this article, we first present surface microfluidic networks microfabricated by a single-step lithographic process using a novel superhydrophobic photosensitive nanocomposite formula. The photopatternable superhydrophobic nanocomposite (PSN) incorporates PTFE nanoparticles into a SU-8 matrix, in which superhydrophobicity (contact angle of above 160°) is primarily contributed by the extremely low chemical energy and nano-topology of PTFE nanoparticles, while the SU-8 polymer matrix offers photopatternability (lithographic resolution of 10 μm) and substrate adhesion. Moreover, an additive intermediate layer with hydrophilic sidewall considerably reduces flow resistance while improving the substrate adhesion, as a crucial improvement from the previous surface flow configuration. Furthermore, self-propelled microfluidic networks driven by surface tension-induced pressure gradient have been fabricated and characterized to demonstrate the applicability of the novel nanocomposite fabrication approach.     

A polymer-metal hybrid flexible mould and application for large area hot roller embossing

In this paper, we report a novel approach to fabricate a low cost, large area and flexible mould and its applications in large area roller embossing. A liquid crystal polymer (LCP) film, which had a high glass transition temperature of 280°C, was clad with copper foils on both sides, was used as a starting material for mould fabrication. The LCP film and the copper foils were 50 and 36 μm thick, respectively. The LCP-Cu flexible mould was obtained through photolithographic patterning and wet etching of the copper foil on top surface of the LCP film. Using this proposed method, a polymer-metal hybrid flexible mould with an area of 150 mm × 150 mm was fabricated. The fabricated mould has a minimum feature size of 25 μm, and has been successfully used to demonstrate large area micro roller embossing. Micro channels, micro dots and micro mixers were embossed on polymeric as well as ceramic green substrates.     

Laser polishing and 2PP structuring of inside microfluidic channels in fused silica

This study presents the development of post-processing steps for microfluidics fabricated with selective laser etching (SLE) in fused silica. In a first step, the SLE surface—even inner walls of microfluidic channels—can be smoothed by laser polishing. In addition, two-photon polymerization (2PP) can be used to manufacture polymer microstructures and microcomponents inside the microfluidic channels. The reduction in the surface roughness by laser polishing is a remelting process. While heating the glass surface above softening temperature, laser radiation relocates material thanks to the surface tension. With laser polishing, the RMS roughness of SLE surfaces can be reduced from 12 µm down to 3 nm for spatial wavelength λ < 400 µm. Thanks to the laser polishing, fluidic processes as well as particles in microchannels can be observed with microscopy. A manufactured microfluidic demonstrates that SLE and laser polishing can be combined successfully. By developing two-photon polymerization (2PP) processing in microchannels we aim to enable new applications with sophisticated 3D structures inside the microchannel. With 2PP, lenses with a diameter of 50 µm are processed with a form accuracy rms of 70 nm. In addition, this study demonstrates that 3D structures can be fabricated inside the microchannels manufactured with SLE. Thanks to the combination of SLE, laser polishing and 2PP, research is pioneering new applications for microfluidics made of fused silica.     

Application of micro structured photosensitive glass for the gravure printing process

Photosensitive glasses are well known as materials which are micro structurable with a high aspect ratio of 20:1. Typical applications are micro mechanical, fluidic and optical components due to the very good chemical, thermal and mechanical stability of this material. Currently the aim of the work is the development of micro structured clichés made from photosensitive glass for the gravure printing of electrically functionalised inks on flexible substrates. Glass clichés with a geometrical variation of recessed cells were fabricated and tested regarding the chemical and mechanical stability using process comparable conditions. Printing tests using particle less and particle loaded electrically functionalised inks were carried out to investigate the influence of cell geometry on printed ink layers. It was found that precise dot structures will be printable if cell openings are <80 μm and cell depths are <30 μm. Resulting from this ITO was printed on flexible glass substrates with a thickness of 30 μm for high temperature treatments.     

A printed circuit board capacitive sensor for air bubble inside fluidic flow detection

This paper presents a three-electrode capacitive fluidic sensor for detecting an air bubble inside a fluidic channel such as blood vessels, oil or medical liquid channels. The capacitor is designed and fabricated based on a printed circuit board (PCB). The electrodes are fabricated by using copper via structure through top to bottom surface of the PCB. A plastic pipe is layout through the capacitive sensor and perpendicular to the PCB surface. Capacitance of sensor changes when an air bubble inside fluidic flow cross the sensor. The capacitance change can be monitored by using a differential capacitive amplifier, a lock-in amplifier, filter and an NI acquisition card. Signal is processed and calculated on a computer. Air bubble inside the liquid flow are detected by monitor the unbalance signal between the three electrode potential voltages. Output voltage depends on the volume of the air bubble due to dielectric change between capacitor’s electrodes. Output voltage is up to 53 mV when an 2.28 mm³ air bubble crosses the sensing channel. Air bubble velocity can be estimated based on the output pulse signal. This proposed fluidic sensor can be used for void fraction detection in medical devices and systems; fluidic characterization; and water–gas, oil–water and oil–water–gas multiphase flows in petroleum technology. That structure also can apply to the micro-size for detecting in microfluidic to monitor and control changes in microfluidic channels.     

Microfluidic chips for cells capture using 3-D hydrodynamic structure array

Microfluidic chips were designed and fabricated to capture cells in a relative small volume to generate the desired concentration needed for analysis. The microfluidic chips comprise three-dimensional (3-D) cell capture structures array fabricated in PDMS. The capture structure includes two layers. The first layer consists of spacers to create small gap between the upper layer and glass. The second layer is a sharp corner U-shaped compartment with sharp corners at the fore-end. And another type capture structure with Y-shaped fluidic guide has been designed. It was demonstrated that the structures can capture cells in theory, using Darcy–Weisbach equation and COMSOL Multiphysics. Then yeast cell was chosen to test the performance of the chips. The chip without fluid guides captured ~1.44 × 10⁵ cells and the capture efficiency was up to 71 %. And the chip with fluid guides captured ~5.0 × 10⁴ cells and the capture efficiency was ~25 %. The chip without fluid guides can capture more cells because the yeast cells in the chip without fluid guides are subject to larger hydrodynamic drag force.     

A novel bending microactuator with integrated flexible electro-rheological microvalves using an alternating pressure source for multi-actuator systems

This paper presents a novel bending microactuator with integrated flexible electro-rheological microvalves (FERVs) using an alternating pressure source for multi-actuator systems. The proposed bending microactuator is a fluidic elastomer actuator that has two fluidic chambers inside and can bend with the chamber pressures controlled by the integrated FERVs, each of which has a flexible structure and changes a flow of electro-rheological fluid (ERF) through its viscosity change due to an applied electric field. The utilization of the FERVs in the actuator reduces the overall size, while the benefits of the alternating pressure source are reduction of the number of pipes in a multi-actuator system and removal of the fluid reservoir tank. The mathematical models were demonstrated and utilized for optimizing and designing the dimensions of the actuator to obtain the maximum bending angle, the fast response, and the highest output force. The designed actuator was successfully fabricated using MEMS technologies and experiments were conducted to investigate the bending angle and the response time of the successfully fabricated actuator. The results showed good agreement between the experimental results and the simulation results, which proved the validity of the proposed models. Comparing with the previously proposed microactuator with an FERV, the proposed actuator had 4.5 times larger bending angle. From the results, the optimized actuator showed the feasibility for use in e.g. micro gripper application.

     

Effect of micro tensile sample’s cross section shape on the strength of weld line in micro injection molding process

As a suitable mass and cost efficiency fabrication method, micro injection molding is doing a very good performance in micro plastic parts production. The mold design is an important part affecting micro parts properties. In this study, a micro injection mold with multi cavities of micro tensile bar is used. These micro cavities are fabricated by a micro milling process in different cross section shapes (semicircle R = 0.5 mm, equilateral triangle D = 0.3 mm, and trapezoid D = 0.336 mm t = 0.2 mm bottom angle = 95°). With an Arburg^® 320C injection molding machine, micro tensile test sample are prepared in different processing parameters so that a correlation between the cross section shapes with micro weld line strength in different conditions could be investigated by tensile test. Final results show that when the cross section shape is different, their corresponding weld line strength is also different. Equilateral triangle cross section is leading to strongest weld line, and then followed by trapezoid, semi-circle is the last. By analysis of these tensile test results, the quantitative factor a is defined as the ratio of perimeter to area of cross section shape, and higher a value is corresponding stronger weld line. After weld line strength comparison in different processing conditions, the results show that higher injection pressure induced to lower weld line strength whatever the cross section shape is. By higher mold and melt temperature, equilateral triangle cross section gives improved weld line strength. But mold and melt temperature affect weld line strength negative for other cross section shapes.     

SU8-micromechanical structures with in situ fabricated movable parts

 We report on the versatile application potential of SU8 photoepoxy for movable micromechanical components. Its outstanding resolution, aspect ratio, and attainable film thicknesses enable the design of structures that allow lateral mechanical interaction of voluminous micro parts. We additionally developed a sacrificial layer process enabling the release of in situ fabricated micro parts as well as large area parts used for capping and packaging. The applicability of this technology is demonstrated on gearwheels in a turbine configuration, a micro fluidic channel with integrated check valve, and an advanced multilayer capping technology with precise feather key fit. Received: 10 August 2000/Accepted: 24 September 2001     

Fabrication of micro-capacitive inclination sensor by resin molding

Capacitive inclination sensors have the advantage that they can easily provide a linear analog output with respect to inclination. Although inclination sensors featuring this advantages are already commercially available, they are generally too large. We fabricated a micro-capacitive inclination sensor by a combination of a resin forming method and a mold. Electrodes of the sensor are 40 μm in a gap and 12 mm² in area. The sensor detects difference of capacitance, which varies with movement of silicone oil accompanying with inclination of the sensor. Since the dimensions of the sensing region are 5 × 5 × 3 mm³ this inclination sensor is expected to be widely used in fields where efficient and reliable position control is a primary factor to be considered. The use of resins is also expected to contribute to a reduction in the costs of materials. We successfully fabricated a micro inclination sensor as a molded product. In future, we will wire up the device to complete this inclination sensor, and will then conduct performance evaluations. If techniques using resin-molded parts are introduced to the low-cost mass-production of Micro Electro Mechanical Systems devices, the range of applications will further expand to new areas of technology and industry.     

Micro-ball lens array fabrication in photoresist using PTFE hydrophobic effect

This paper presents a simple method for fabricating a micro-ball lens and its array. The core technology involves the hydrophobic characteristics of polyterafluoroethylene (PTFE) substrate. High contact angle between the melted photoresist pattern and PTFE generates the micro-ball lens and array. The PTFE thin film is spun onto a silicon wafer and oven dried. Photoresist AZ4620 is used to pattern micro-columns with various diameters; 60, 70 and 80 μm. A thermal reflow process is then applied to melt these micro-column patterns into a micro-ball lens array. The achieved micro-ball lens array has a diameter of 98 μm fabricated using 80 μm diameter patterns. This method provides a simple fabrication process and low material cost.     

MEMS-based combustor with hairpin-shape design of gas recirculation channel

This paper describes the design, fabrication and test of a silicon-based micro combustor, which is a part of a micro power generation system under development. Based on the three-dimensional computational fluid dynamics (CFD) simulation and analysis of different micro combustor design, a hairpin-shape design for air/fuel recirculation channel is adopted. The combustor is fabricated from seven single crystal silicon wafers using deep reactive ion etching (DRIE) process. It has been assembled successfully with gas tubing and thermal couplers for monitoring the exit gas temperature. The effect of mass flow rate on the combustion characteristics is studied experimentally and numerically under several operating conditions. The exhaust gas temperature can reach the range from 870 to 1,100 K. The results indicate that with the increases of the mass flow rate, the combustor exhaust gas temperature increase as well in both experimental and the simulated results. This is due to the heat released in the combustor increases with the fuel/air mass flow rate.

     

Microphotometric characterization of fluid segment populations generated in different simple microfluidic networks

The stability of fluid segments is limited by deformation stress and by coalescence events. Both factors are typical for the passage of fluid segments through microfluidic networks. Therefore, the coalescence behaviour of micro fluid segments in simple network structures in dependence of flow rate ratios was investigated and characterized by the composition of obtained segment populations. Series of segments of different size and distance were generated either in a double T- or in a triple T-arrangement. PTFE elements were used for the micro fluid network. Nearly pulsation-free fluid actuation was realized by syringe pumps. The flow conditions in the input streams of carrier liquid and injected solutions remained constant during the experiments. Segment sequences become divers by different injection, stacking and coalescence events. The resulting segment sequences were characterized by on-line micro photometry. The populations of obtained micro fluid segments during each experiment were characterized by the distribution of segment size and segment distance or segment period, respectively. Microfluidic experiments as well as the numerical simulations support the assumption that the character of segment populations is mainly determined by the flow rate ratios and by the coalescence sensitivity beside the topology of the fluidic network.     

Micro injection molding for mass production using LIGA mold inserts

Micro molding is one of key technologies for mass production of polymer micro parts and structures with high aspect ratios. The authors developed a commercially available micro injection molding technology for high aspect ratio microstructures (HARMs) with LIGA-made mold inserts and pressurized CO₂ gasses. The test inserts made of nickel with the smallest surface details of 5 μm with structural height of 15 μm were fabricated by using LIGA technology. High surface quality in terms of low surface roughness of the mold inserts allowed using for injection molding. Compared to standard inserts no draft, which is required to provide a proper demolding, was formed in the inserts. To meet higher economic efficiency and cost reduction, a fully electrical injection molding machine of higher accuracy has been applied with dissolving CO₂ gasses into molten resin. The gasses acts as plasticizer and improves the flowability of the resin. Simultaneously, pressurizing the cavity with the gasses allows high replication to be obtained. Micro injection molding, using polycarbonate as polymer resins, with the aspect ratio of two was achieved in the area of 28 × 55 mm² at the cycle time of 40 s with CO₂ gasses, in contrast to the case of the aspect ratio of 0.1 without the gasses.     

MEMS-based combustor with hairpin-shape design of gas recirculation channel

This paper describes the design, fabrication and test of a silicon-based micro combustor, which is a part of a micro power generation system under development. Based on the three-dimensional computational fluid dynamics (CFD) simulation and analysis of different micro combustor design, a hairpin-shape design for air/fuel recirculation channel is adopted. The combustor is fabricated from seven single crystal silicon wafers using deep reactive ion etching (DRIE) process. It has been assembled successfully with gas tubing and thermal couplers for monitoring the exit gas temperature. The effect of mass flow rate on the combustion characteristics is studied experimentally and numerically under several operating conditions. The exhaust gas temperature can reach the range from 870 to 1,100 K. The results indicate that with the increases of the mass flow rate, the combustor exhaust gas temperature increase as well in both experimental and the simulated results. This is due to the heat released in the combustor increases with the fuel/air mass flow rate.