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ABSTRACT: Electrohydrodynamic patterning of polymer is a unique technique for micro- and nano-structuring, where an electric voltage is applied to an electrode pair consisting of a patterned template and a polymer-coated substrate either in contact or separated by an air gap, to actuate deformation of the rheological polymer. Depending on the template composition, three processes were proposed for implementing the EHDP technique and have received a wide attention, i.e., electrostatic force-assisted nanoimprint, dielectrophoresis-electrocapillary force driven imprint and electrically induced structure formation. A numerical approach, which is versatile for visualizing the full evolution of micro- or nano-structures in these patterning processes or their variants, can be desirable as a critical tool for optimizing the process variables in industrial applications of this structuring technique. Considering the fact that all these processes use a dielectric and viscous polymer (behaving mechanically as a liquid) and are carried out in ambient air, this paper presents a generalized formulation for numerical characterization of the EHDP processes, by coupling liquid dielectrophoresis (L-DEP) and phase field of air-liquid dual phase. More importantly, some major scale effects, such as surface tension, contact angle, liquid-solid interface slip, non-Newtonian viscosity law, are introduced, which can impact on the accuracy of numerical results tremendously, as shown experimentally by our electrical actuation of a dielectric micro-droplet as a test problem. The numerical results have well agreed with or well explained experimental observations so far published for the three EHDP processes.
Langmuir 03/2013; · 4.19 Impact Factor
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ABSTRACT: The ability to generate a large area micropillar array with spatially varying heights allows for exploring numerous new interesting applications in biotechnology, surface engineering, microfluidics, etc. This letter presents a clever and straightforward method, called electrically modulated microtransfer molding (EM3), for generating such unique micro-structures from a silicon mold arrayed with microholes. The key to the process is an application of electrically tunable wettability caused by a spatially modulated voltage, which electrohydrodynamically drives a photo-curable and dielectric prepolymer to fill the microholes onto a depth depending on the voltage amplitude. Using EM3, micropillar arrays with step-wise or continuously varying heights are successfully fabricated, with the diameter scalable to 1.5 µm and with the maximum height being equal to the depth of the high-aspect-ratio (more than 10:1) microholes.
Langmuir 01/2013; · 4.19 Impact Factor
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ABSTRACT: Y. C. Ding, J. Y. Shao, and co-workers demonstrate a creative and economic method for manufacturing large-area microlens arrays (MLAs) with controllable curvature and supersmooth surfaces. On page OP 165, the production of a concave MLA is achieved by electrohydrodynamically deforming the surface of a photocurable prepolymer trapped in microhole array which has been etched onto a doped silicon wafer. The concave MLA is then used as a master to generate the convex MLA via vacuum micromoulding.
Advanced Materials 06/2012; 24(23):OP90. · 13.88 Impact Factor
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ABSTRACT: UV-nanoimprint lithography (UV-NIL) using a soft mold is a promising technique with low cost and high throughput for producing
the submicron scale large-area patterns. However, the deformations of the soft mold during imprinting process which can cause
serious consequences have to be understood for the practical application of the process. This paper investigated the deformation
of the soft mold by theoretical analyses, numerical simulations, and experimental studies. We simulated the mold deformation
using a simplified model and finite element method. The simulation and the related experimental results agree well with each
other. Through the investigation, the mechanism and affected factors of the mold deformation are revealed, and some useful
conclusions have been achieved. These results will be valuable in optimizing the imprinting process conditions and mold design
for improving the quality of transferred patterns.
Science in China Series E Technological Sciences 04/2012; 52(2):294-302. · 1.02 Impact Factor
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ABSTRACT: The microlens array (MLA) or micromirror array (MMA) is one of the most important units in many optical devices and photoelectronic systems. The paper presents a process for fabricating an MLA with well-controlled curvature by liquid trapping and electrohydrodynamic deformation in microholes. The approach has been shown capable of generating large-area and high-quality MLAs or MMAs economically.
Advanced Materials 03/2012; 24(23):OP165-9, OP90. · 13.88 Impact Factor
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ABSTRACT: A barrel-shaped metal/insulator/metal (MIM) field-emission cathode, also referred to as a field-emission cannon, is constructed using conventional SU-8 UV lithography combined with sputtering and lift-off processes. An array of these field-emission cannons has demonstrated uniform field emission in a luminescent pixel array. The field-emission test proves that the unique geometry of the field-emission cannon significantly improves field-emission efficiency and electron beam focus. Detailed data analysis has revealed that both conventional sharp edge field emission and MIM field emission contribute to the total emission current. The field emission starts from an edge emission at gate voltages (Vg) below 8 V. When Vg increases above 8 V, electrons tunnel into the cannon through the thin SiO2 layer and inner metal layer (i.e., the gate electrode). Thus, the MIM field emission starts to dominate.
Nanotechnology 11/2011; 22(45):455302. · 3.98 Impact Factor
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ABSTRACT: This Letter presents a method for fabricating concave microlens arrays of UV-curable polymer by using the dielectrophoresis (DEP) force. The DEP force, generated by a voltage between the patterned conductive template and substrate, acting on the polymer-air interface, can drive the dielectric liquid polymer into the template holes and change the shape of the polymer-air interface. The upper polymer surface of fabricated microlens is super smooth, which can reduce optical noise. The upper surface geometry is measured approximately as parabolic in general, which can lead to a negligible spherical aberration, compared to spherical surfaces.
Optics Letters 10/2011; 36(20):4083-5. · 3.40 Impact Factor
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ABSTRACT: Electrohydrodynamic (EHD) patterning is a process for electrically transferring the micro- or nano-structures on a template onto a thin polymer film. The process involves applying an electric field to the patterned template and the substrate, which results in the template and substrate behaving like an electrode pair. The height of replication for EHD patterning has been limited at the nano-scale in previously proposed techniques because the electric field is sensitive to the spacer height of the template. In this paper, we investigate the influence of the template-modulated electric field on the formation of replication. We show that templates with conductive patterns allow for large field changes and enlarge the spacer height. Replication heights ranging from 1.5 to 8 µm can be achieved using templates with conductive patterns.
Journal of Micromechanics and Microengineering 10/2011; 21(11):115004. · 2.11 Impact Factor
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ABSTRACT: Electrically induced patterning process, as a novel micro- or nano-structuring approach for fabrication of various micro- or nano-systems, is usually implemented by applying a voltage to an electrode pair consisting of a patterned or non-patterned template and a polymer-coated substrate separated in parallel by an air gap, followed by photo- or thermo-curing of the fluidic and dielectric polymer. The analyses performed so far to characterize this patterning process have been based on linear thermodynamics for a thermally instable thin film perturbed by an electrostatically induced hydraulic pressure. For mathematical simplicity, these analyses were formulated only for a flat template and a flat film surface with infinite planar area, demonstrating the tendency of initial pattern growth on the polymer film, but being unable to visualize the dynamic evolution of micro- or nano-structure growth throughout the patterning process for a real-life template in practical applications. This paper attempts to provide another insight into this patterning process from a viewpoint of liquid dielectrophoresis (L-DEP), by presenting an approach for numerical simulation of the patterning process based on a coupling of L-DEP and two-phase flow theories. First, a numerical analysis has been made for the electrocoalescence of a water droplet with bottom water in silicone oil to benchmark effectiveness of the proposed numerical approach against published experimental observations. More numerical results have then been provided to show effects of some process variables on the evolution of the polymer micro- or nano-structures for this patterning process.
Electrophoresis 07/2011; · 3.30 Impact Factor
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ABSTRACT: We propose a novel method for fabricating high-aspect-ratio micro-/nano-structures by dielectrophoresis-electrocapillary force (DEP-ECF)-driven UV-imprinting. The force of DEP-ECF, acting on an air–liquid interface and an air–liquid–solid three-phase contact line, is generated by applying voltage between an electrically conductive mold and a substrate, and tends to pull the dielectric liquid (a UV-curable pre-polymer) into the mold micro-cavities. The existence of DEP-ECF is explained theoretically and demonstrated experimentally by the electrically induced reduction of the contact angle. Furthermore, DEP-ECF is proven to play a critical role in forcing the polymer to fill into the mold cavities by the real-time observation of the dynamic filling process. Using the DEP-ECF-driven UV-imprinting process, high-aspect-ratio polymer micro-/nano-structures (more than 10:1) are fabricated with high consistency. This patterning method can overcome the drawbacks of the mechanically induced mold deformation and position shift in conventional imprinting lithography and maximize the pattern uniformity which is usually poor in capillary force lithography.
Journal of Micromechanics and Microengineering 05/2011; 21(6):065010. · 2.11 Impact Factor
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ABSTRACT: In this paper, we present a new method to realize anisotropy by restricting a droplet on an unstructured Si hydrophobic domain between two superhydrophobic strips fabricated by femtosecond laser. The water contact angles and corresponding water baseline length were investigated. The results showed that anisotropy would vary with the volume-induced pinning-depinning-repinning behavior of the droplet. Furthermore, through the observation of water response on small Si domain, the adhesive force of the structure is proven to be the key factor giving rise to the anisotropy wetting. This phenomenon could potentially be used as a model for fundamental research, and such structures could be utilized to control large volume in microfluidic devices, lab-on-chip system, microreactors, and self-cleaning surfaces.
Langmuir 01/2011; 27(1):359-65. · 4.19 Impact Factor
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ABSTRACT: This work was partly supported by the 973 Basics Science Research Program of China (Grant No. 2009CB 724202), National Science Foundation of China (Grant No. 50775176) and National Science Foundation of Shandong Province (Grant No.Y2007F49).
02/2010; , ISBN: 978-953-307-064-3
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ABSTRACT: Roller imprint is considered as one of the processes suitable for patterning on a large-area flexible substrate, which is critical for macroelectronics manufacturing. In contrast to other published roller imprint processes (such as hot-embossing roller imprint or ultraviolet roller imprint), the roller-reversal imprint (RRI) process investigated in this paper starts with pattern coating of an ink (mostly a liquefied electronics material, such as a semiconductor polymer) on a mould roller and ends with transferring the ink already patterned on the roller to the substrate, so it can obtain micropatterns with a precise profile yet leave no residual film on the substrate. One of the critical issues in obtaining patterned ink on the substrate with the required profile by the RRI process is to ensure a complete ink transfer from the microcavities on the mould roller onto the substrate. In this paper, a mathematical model is proposed to analyze the mechanics of the ink transfer, and a criterion for a complete ink transfer is derived. Furthermore, the effects of imprint force on the ink transfer are also demonstrated by an analysis of the elastic deformation of the substrate. The simulations and corresponding experiments show that the ink transfer in the RRI process is strongly dependent on the ratio of work of adhesion at the ink–mould and ink–substrate interfaces, and the critical ratio for a complete ink transfer is determined mainly by the profile of microcavities on the mould featured by the aspect ratio and the sidewall angle. The ink transfer model can be used to select proper materials (including the ink, surface energies of the mould roller and substrate) in the RRI process, and can also be regarded as a guideline for profile designing of the microcavities on the mould roller used in the RRI process.
Journal of Micromechanics and Microengineering 12/2008; 19(1):015033. · 2.11 Impact Factor
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ABSTRACT: This paper presents a novel reverse engineering digitizing system for full part geometry, which is based on a cross-sectional
imaging device built in a NC milling machine. The system successively captures a picture for each planar cross-section contour
of the part by end-milling and CCD imaging, and builds the geometry for both external and internal surfaces of the complex
3D part based on a set of the vectored cross-sectional contours. The system mainly consists of three components: a NC milling
machine, a cross-sectional imaging device and a computer control unit. Some issues involving the principle and process flow
of the system, encasing materials, cross-sectional imaging and NC code generation, etc. are described in detail. Built on
an existing NC milling machine, a portable device for capturing the cross-sectional images is designed, which includes an
isolated light source, a digital camera, a protective case, a rigid arm and a robust tripod. The device, connected to a computer
control unit, serves as a highly flexible accessory for the NC milling machine, constructing the cross-sectional imaging system
for reverse engineering. Furthermore, the error analysis and accuracy assessment of the system are also addressed. A typical
case is discussed in detail to illustrate the applications of the system. Such a re-configurable digitizing system for reverse
engineering offers a number of advantages, such as the functional extension of an existing NC milling machine, low costs,
and rapid construction. As a result, this system provides a feasible and useful scheme for many enterprises to construct their
own reverse measuring system based on existing equipment to aid in rapid product development and extend the function of existing
equipment.
International Journal of Advanced Manufacturing Technology 01/2008; 37(3):341-353. · 1.10 Impact Factor
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Computers in Industry. 01/2008; 59:777-785.
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ABSTRACT: A nano-imprint lithography (NIL) technology is approached to fabricate the organic hetereo-structure of the photovoltaic (PV) device. Experimental results reveal that fabrication of PV devices can improve its power conversion.
Nano-Optoelectronics Workshop, 2007. i-NOW '07. International; 09/2007
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ABSTRACT: This paper proposes a UV imprint lithography process which uses a soft PDMS mold to transfer high resolution patterns at room temperature and low pressures conditions, and emphasizes reporting the development of the step micro-imprint lithography (SIL) tool for sub-micrometer patterning. The overall design of the machine and implementation of key units are described in detail. To eliminate the distortion of the soft mold in the loading process, distortion reduction by a load release process was proposed and applied in the SIL machine. By optimizing the loading process curve, an imprinting process curve was established. Furthermore, an overlay process using the load release and alignment error pre-compensation method was proposed to achieve high precision overlay for the SIL tool. Finally, various experiments were conducted to test the performance of the SIL apparatus. The experimental results show that the step micro-imprint lithography tool together with the proposed processes can replicate the sub-micrometer patterns with different feature sizes, different structures and different pattern sizes.
Journal of Micromechanics and Microengineering 09/2007; 17(10):2039. · 2.11 Impact Factor
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ABSTRACT: Imprint lithography has been gaining popularity as a new method to fabricate microelectro mechanical systems. The main advantages of the IL are its extremely low set-up cost, high replicating accuracy and extended fabricating critical dimension. Compare to traditional optical lithography, IL has the advantages of being able to fabricate complex pattern structure with high-aspect ratio. However, the thermal and loading errors can reduce pattern transferring fidelity. In this paper, UV curing method is used in IL process which can avoid the heat distortion of tools. Additionally, a six-step loading process for template pressing into resist film is developed. The performance of this process include: the loading locus is continuous with very high accuracy (10nm), the press releaseing control (accuracy up to 1 psi) can reduce and avoid the distortion of template structure and stage supports. This process can achieve a residual layer with thickness of 20nm and avoid the elastic stamp distorted (under 20nm) at the same time. The press force can reach up to 300 psi for 6 cm2 pattern size but the friction force during demould process can be reduced to 30 psi. Experimental results reveal that it is a novel and robust process with high fidelity in micro/nano structures manufacturing.
Journal of Physics Conference Series 04/2006; 34(1):506.
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ABSTRACT: This paper presents a simple and reliable imprint template fabrication process for MEMS based on glass wet etching using a single-layer photoresist as the etching mask. In this work a novel vapour deposition process is adopted to cover a thin layer of silane coupler on the glass surface to improve the adhesion strength of the resist and hence attenuate the undercutting phenomenon, which reduces the extra undercut ratio to 0.6 and improves the sharpness of the etched pattern edges. Since the air bubbles in the photoresist and the particle contamination on the glass surface will cause some defects on the etched surface, the authors adopted a thick layer of resist to eliminate defects and reduce the stringent requirement for clean-room conditions. A smooth template surface is obtained by using hydrochloric acid as an etching agent additive, which can facilitate the template separation in the imprint lithography process. Imprint templates with a pattern feature size of 100 µm have been fabricated using the developed process and the imprint results are demonstrated.
Journal of Micromechanics and Microengineering 02/2006; 16(3):564. · 2.11 Impact Factor
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ABSTRACT: This paper presents the design of an ultra precision positioning system, which consists of a coarse stage and a fine stage. Two servo motors moving on recirculating ball screw are used to drive the coarse stage and three piezo actuators are used to provide the nanoscale positioning. The static and dynamic performances of the positioning system are formulated for designing the micro stage. Based on an evaluation of the system's natural frequency, a dual sever loop approach is used as the control mechanism. The main noise caused by the ambient environment is reduced by a vibration-suppressing table, and in the system control software, a digital Chebyshev filter is used to remove the noise caused by the magnetic chuck on the table. To correct the hysteresis and nonlinearity of PZT, Exact Model Matching (EMM) control law has been used, and therefore repeatability of the fine stage's motion can be improved considerably, the positive and negative movement can follow exactly the same path. A positioning accuracy of 8 nm is achieved over a traveling range of 200 mm with this system.
Journal of Micromechanics and Microengineering 01/2003; 13(2):295. · 2.11 Impact Factor
