Papers by Keyword: Micro-Fabrication

Abstract: In this paper, we propose a new approach for fabrication processes of microstructures composed of diffractive optical elements (DOE) and security elements. The holographic lithography is combined with laser lithography to obtain highly secured holographic labels for products protection. The secret key is an untraceable and hardly reproducible geometry and can be embedded in the labels or stickers to increase the level of security and diminish the possibility of products counterfeiting. In our process, the holographic structure composed of DOEs, and the key are designed separately by two authorized designers and recombined using double exposure followed by a single development step. The layout of microstructures that composes the security key are known only by the designer.

Abstract: The microfluidic has been applied to the field of bio-medicine, micro fluidic electronic in recent years. In this paper we reported a simple methodology to fabricate PDMS microfluidic channels. The method consists of three main fabrication steps: (1) Direct write the micrometric PCL 2D or 3D pattern by the near-field melt-electrospinning. (2) Cast the PDMS on the printed PCL pattern. (3) Completely remove the embedded sacrificial PCL layer by soaking and flushing with acetone. Uniformity of the morphology of the micro channels and well-alignment could be easily achieved due to include the dimensions achievable using this method. We have also designed and fabricated a few micro fluidic channels. SEM and white-light interferometer images were taken to illustrate the characters of essential parts. This work demonstrated the potential utilization of this technique.

Abstract: Research on Micro air vehicle (MAV) has been carried out by many researchers to gather information in environmental monitoring, security and so on. When the earthquake, fire, smoke take place, it is difficult for human beings to investigate the detail because of dangerous condition. However, MAV has possibility to investigate the detail because MAV can fly freely around. Recently, dragonfly is highly focused by many researchers because dragonfly has high flight performances those are high efficiency flight, unintended acceleration, rapid turn and hovering. In general, these characteristics have root that wing is corrugation shape. We focus on microstructures on wing and its aerodynamic characteristics because there are many unique microstructures. We focused on micro spikes on dragonfly wing. Over three thousands of spikes exist on two sides of wing. The length and shape of spikes are 10 to 100 micron meters and oblique circular cone. It is important to clear the aerodynamic effect of the oblique circular cone. Artificial wing was fabricated by following processes. We fabricated micro spikes utilizing electro polishing. Fabricated micro spikes were set on plate utilizing micro spot bonding. We investigated the flow around the artificial wing and found that the flow around wing was controlled by micro spikes on wing. In this paper, we focused on comb shape of leading edge of wing. Comb shape is fabricated utilizing micro-EDM. We investigate flow characteristics of comb shape.

Abstract: Electroforming technology is an important part of micro fabrication andfine parts and composite materials prepared by the electroforming technology has broad application prospects. This paper describes the principle and method of electroforming, introduces the development and the basic elements of electroforming, then concludes the research status and main research direction and trend of this technology.

Abstract: The aim of this scientific work is to present different piezoresistive materials suitable to be integrated into micromechanical force sensors. As material for the mechanical structure of the sensors SU-8 has been chosen because it features favorable characteristics, such as flexible and simple fabrication of micro components through the use of standard UV lithography for forming three dimensional geometries such as cantilevers and membranes. In addition, on the basis of a significantly lower Young’s modulus compared to silicon, great opportunities to improve the force sensitivity of such sensors are offered by SU-8.However, SU-8 photoresist does not have piezoresistive properties, and therefore it has to be combined with an additional, beneficial piezoresistive material. A well-controlled and frequently used material for piezoresistive elements is doped silicon. This paper provides an overview of characteristics such as gauge factor and temperature coefficient of resistance (TCR) for a variety of commonly used piezoresistive materials, namely metals, silicon, conductive composite materials and diamond-like carbon. As a characteristic factor for the estimated sensitivity of the force sensor, the ratio of the gauge factor k to the Young´s modulus E of the structural material is presented for the different material combinations. A classification of conventional silicon based tactile force sensors is made to build a basis for comparison. Furthermore the suitability of different piezoresistive materials for the integration into an SU 8-based sensor is investigated.

Abstract: Monitoring body fluids such as sweat composition can provide useful information about the physiological status. Physiological monitoring of body fluids such as sweat with a textile-based system has the advantage of being non-invasive and easily accessible and such monitoring is beneficial to indicate information about body's physiological status. In the present study, it is aimed to design a textile-based system with non-invasive methods which can be used to monitor a sportsman's performance. A novel, disposable and wearable biochemical analytical device was designed and fabricated by patterning micro channels and reservoirs using SU-8 photoresist through photolithography technique on an absorbant bicomponent Evolon® nonwoven substrate. It was obtained that hydrophilic reservoirs were well defined and demarcated by hydrophobic barriers. Therefore, no liquid leakage was observed around the reservoirs which was crucial for achieving a proper enzyme immobilization and the successful detection of the color change after the simulated sweat was deposited on the hydrophilic reservoir areas. Analyte optimization studies revealed that color change became more evident with the increasing analyte concentration until 20 mM and started to decrease with further increase due to analyte inhibition. Also, on textile fabrics, color densities started to decrease after 40 mM analyte concentration.

Abstract: In this study, capabilities of zinc oxide (ZnO) thin films in sensing and actuating were investigated using micromachined micro-cantilevers. A heterogeneous piezoelectric cantilever was modeled to study its response under voltage and/or external mechanical loading. A ZnO thin-film micro-cantilever was designed based on the developed theoretical model. Simulated tip deflections of the micro-cantilever were on the nanometer level under typical electrical and mechanical input. A prototype was fabricated with microfabrication techniques. The ZnO thin film was sputtered at room temperature and demonstrated good compatibility with common chemicals and processes in micromachining. The fabricated micro-cantilever was experimentally characterized for its actuating and sensing performance. For actuator characterization tip deflection of the micro-cantilever was detected by a laser Doppler vibrometer, while for sensor characterization the micro-cantilever was calibrated as an acceleration sensor using a reference accelerometer. The experimental resonant frequency, actuating and sensing sensitivities agreed well the design specifications.

Abstract: A fatigue testing setup based on electromagnetic excitation was built to apply cyclic stresses to the specimens near their resonance frequency. A test near the resonance frequency has the advantage that higher stresses can be applied to test specimens at a reduced input power. Stress amplitude up to 1000 MPa can be applied to the test specimens and up to four specimens can be tested simultaneously. The setup can test specimens at high fatigue cycle regime i.e. 100 million stress cycles can be achieved in 48 hours.The setup has been used to study the effects of internal and external microstructure on the fatigue strength of materials. Specimens especially stainless steel-304 was prepared by different techniques i.e. electric discharge machining EDM, etching and laser cutting. Specimens prepared by these techniques were tested and their fatigue strengths were compared. To probe the material endurance limit, tests were also performed on the above mentioned steel specimens in very high stress cycle regime i.e. > 10⁹ cycles. In order to investigate the effect of internal microstructure on fatigue strength of material, CuZn37 fabricated by etching was tested and the effect of different grain size on fatigue strength was compared. SN curves have been plotted for materials with no prior fatigue strength data. Stainless steel-1.4404 specimens prepared by Rapid Prototyping (RP) has been tested for fatigue analysis. The test results showed higher degree of scattering when compared to the traditionally manufactured steel. Fractography revealed the existence of inherent material flaws which was the main reason of higher degree of test point scattering. In addition to these data, the SN curve was plotted for Innolot which is an important soldering alloy and prompts to fatigue failure in electronic assemblies.

Abstract: Microcolumn, a miniaturized electron optical system, is a powerful tool in manipulating electron beam for maskless direct e-beam lithography and miniaturized low voltage SEM for surface inspection, testing, and metrology. The basic parts of microcolumn are electron emitter, source lens, deflector, and Einzel lens. There are still several challenges in optimization of each component for better performance of microcolumn for aberration-free high quality imaging and large field of view. For the improvement of microcolumn, we developed a fabrication technique of making thin electrostatic lens using micro-electromechanical systems (MEMS) processes. Two types of microcolumns have been assembled by varying the spaces between Einzel lens-electrodes, and their performance have been evaluated for the comparison. The scan range is found to be increased with reducing the gap between the lenses and increasing working distance. The effect of the spatial gap on the scan range and image is analyzed through simulation study on the electric potential and field strength.

Abstract: The fabrication of polymer based microfluidic devices using the hot embossing technique and their surface modification for easy fluid flow through the devices has been a growing field of research. During hot embossing, the replication fidelity on polymer substrate not only depends on the processing parameters such as temperature, pressure and time but also on their chemical structure which affects their thermo-dependent viscoelastic properties. For copolymers such as cyclic olefin copolymer (COC) which comprises ethylene and norbornene units, such properties depend on their relative ethylene and norbornene content. We report in this paper, a systematic study of replication fidelity and surface modification on COC polymer with varying norbornene content from 65 to 82 wt%. Replication fidelity which includes the surface morphology and cross-section profiles of the microchannel were characterized using SEM and Confocal microscope respectively. The modified surface was evaluated using Fourier transform infrared spectroscopy (FTIR spectroscopy) and water contact angle measurement. It was observed that in hot embossing, higher norbornene content contributed to good replication fidelity at identical experimental conditions. Furthermore, it was observed that with increase in norbornene content, the grafting efficiency decreases resulting in poor surface modification.