AC-pulse modulated electrohydrodynamic jet printing and electroless copper deposition for conductive microscale patterning on flexible insulating substrates

This paper presents a novel micro-manufacturing method for fabrication of electrical features and patterns on highly insulating substrates and flexible substrates based on high-resolution AC-pulse modulated electrohydrodynamic jet (e-jet) printing of silver nanoink as seed layer followed by electroless copper deposition. Traditional ink jet printing method is limited in printing resolution which is determined by dimension of printing nozzle and dimension of droplets. Traditional e-jet printing has the disadvantage of residual charge problem especially for highly insulating substrates which cannot dredge remained charge of printed droplets, resulting in distorted electrostatic field and low printing controllability. Meanwhile, for printing of liquid phase ink, feature resolution contradicts with the required thickness, which is a key factor of conductivity of printed patterns. In this paper, a novel AC-modulated e-jet printing technique is applied to neutralize charges on substrates by switching polarity of consequent droplets for direct printing of high-resolution conductive silver patterns on insulating substrates. Electroless copper deposition is introduced in the fabrication process to solve the thickness problem of the resulting features. Variables of fabrication process, including amplitude and frequency of AC-pulsed voltage, plotting speed, curing temperature, number of layers, concentration of solution for copper growth, were identified to achieve reliable and conductive printed patterns. Sub-20 µm silver tracks with resistivity about 3.16 times of bulk silver were successfully fabricated. We demonstrated that ac-pulse modulated e-jet printing followed by electroless copper deposition can produce high resolution conductive patterns with improved thickness on insulating substrates and flexible substrates, which can be applied to direct printing and micro scale patterning for flexible electronics and wearable devices applications.     

A computer-controlled near-field electrospinning setup and its graphic user interface for precision patterning of functional nanofibers on 2D and 3D substrates

Electrospinning is a versatile technique for production of nanofibers. However, it lacks the precision and control necessary for fabrication of nanofiber-based devices. The positional control of the nanofiber placement can be dramatically improved using low-voltage near-field electrospinning (LV-NFES). LV-NFES allows nanofibers to be patterned on 2D and 3D substrates. However, use of NFES requires low working distance between the electrospinning nozzle and substrate, manual jet initiation, and precise substrate movement to control fiber deposition. Environmental factors such as humidity also need to be controlled. We developed a computer-controlled automation strategy for LV-NFES to improve performance and reliability. With this setup, the user is able to control the relevant sensor and actuator parameters through a custom graphic user interface application programmed on the C#.NET platform. The stage movement can be programmed as to achieve any desired nanofiber pattern and thickness. The nanofiber generation step is initiated through a software-controlled linear actuator. Parameter setting files can be saved into an Excel sheet and can be used subsequently in running multiple experiments. Each experiment is automatically video recorded and stamped with the pertinent real-time parameters. Humidity is controlled with ±3% accuracy through a feedback loop. Further improvements, such as real-time droplet size control for feed rate regulation are in progress.     

An additive micromolding approach for the development of micromachined ceramic substrates for RF applications

The selective removal of the substrate from under devices can help improve Q-factors, reduce losses and parasitics and can be applied to microwave components (transmission lines, spiral inductors, and capacitors) critical to high-frequency communications systems. A novel molding process has been developed to produce cavities in ceramic substrates over which gold transmission lines can be suspended. The "additive" method of fabricating cavities in ceramics was primarily based on the production of a substrate with preexisting cavities, as opposed to generation of cavities by the removal or the "subtraction" of material. The preexisting cavities were generated using a transfer mold technique based on photolithography, anisotropic silicon etching and nickel electroplating. The approach was demonstrated successfully using a commercial glass ceramic material (DuPont 951 Green Tape) to yield 100-/spl mu/m-deep cavities that showed shape retention and dimensional stability.     

A practical method for patterning lumens through ECM hydrogels via viscous finger patterning

Extracellular matrix (ECM) hydrogels with patterned lumens have been used as a framework to generate more physiologically relevant models of tissues, such as vessels and mammary ducts, for biological investigations. However, these models have not found widespread use in research labs or in high-throughput screening applications in large part because the basic methods for generating the lumen structures are generally cumbersome and slow. Here we present viscous finger patterning, a technique to generate lumens through ECM hydrogels in microchannels that can be accomplished using manual or automated pipetting. Passive pumping is used to flow culture media through an unpolymerized hydrogel, creating a lumen through the hydrogel that is subsequently polymerized. Viscous finger patterning takes advantage of viscous fingering, the fluid dynamics phenomenon where a less viscous fluid will flow through and displace a more viscous fluid. We have characterized the technique and used it to create a variety of channel geometries and ECM hydrogel compositions, as well as for the generation of lumens surrounded by multiple hydrogel layers. Because viscous finger patterning can be performed with automated liquid handling systems, high-throughput generation of ECM hydrogels with patterned lumen is enabled. The ability to rapidly and cost-effectively create large numbers of lumens in natural polymers overcomes a critical barrier to the use of more physiologically relevant tissue models in a variety of biological studies and drug screening applications.     

Design and numerical analysis of interdigitated radiating-strips electrode for uniform 3D dielectrophoretic patterning of liver cells

Microsystem Technologies - This paper presents the design and numerical analysis of a new three-dimensional (3D) electrode having a non-uniform electric field gradient for dielectrophoretic...     

Multilayer patterning technique for micro- and nanofluidic chip fabrication

Polymer micro- and nanofluidic chips become increasingly significant for medical and biological applications. However, it is difficult to fabricate micro- and nanochannels integrately into a polymer substrate due to the reflow and insufficient flow of the polymer. In the present paper, micro- and nanochannels were hot embossed into a multilayer substrate by micromold and nanomold, respectively. To replicate high replication precision nanochannels without damaging the fabricated microchannels, the embossing parameters were optimized by Taguchi and analytic hierarchy process methods. The fabricated micro- and nanochannels were fully sealed at bonding parameters optimized according to the bonding rate of the chip. The fluorescence image indicates that there is no blocking or leakage over the entire micro- and nanochannels. With presented fabrication method, low-cost polymer micro- and nanostructures can be fabricated, which allows for commercial manufacturing of micro- and nanofluidic chips.     

Screen-pad printing for electrode patterning on curvy surfaces

Microsystem Technologies - Pad printing is a simple but effective method for fabricating electrodes onto complex curved surfaces. In this method, ink is picked up from the gravure plate by the soft...     

A method for precision patterning of silicone elastomer and its applications

This paper presents a general microfabrication method for precision patterning of thin-film poly(dimethylsiloxane) (PDMS). The method enables PDMS microstructures with controlled lateral dimensions and thickness on a silicon or glass substrate. Two applications based on this new method are discussed. First, a scanning probe microscopy (SPM) probe with PDMS tip is developed and used for scanning probe contact printing (SPCP). Second, this paper demonstrates surface micromachined membranes with integrated silicone gaskets.     

变量泵控制变量马达系统建模及控制

变量泵控制变量马达系统是一个双输入单输出耦合本质非线性系统, 常规控制方法很难取得满意的控制效果. 针对变量泵控制变量马达系统非线性和不可解耦的特点, 提出基于线性化理论的变量泵变量马达Bang-Bang控制算法. 首先建立变量泵控制变量马达系统数学模型, 模型存在包括输出变量在内的相乘非线性, 然后运用反馈线性化理论将非线性数学模型线性化, 最后提出新的Bang-Bang控制算法实现变量马达的快速控制.仿真研究表明该算法可以实现系统快速控制, 效果优于目前常规控制方法, 而且算法对马达转速和负载变化都具有较强的鲁棒性.     

Ultraviolet embossing for patterning high aspect ratio polymeric microstructures

In ultraviolet (UV) embossing, a substrate with a coating of liquid or semi-solid UV curable resin mix is pressed against a patterned embossing mold. The resin mix is irradiated with UV before demolding of the hardened microstructures. UV embossing can be done at room temperature and low pressure. However, demolding of UV embossed high aspect ratio microstructures from a metallic mold is typically difficult since there is no differential thermal contraction between the mold and the embossing. Several factors have been identified to influence demolding of UV embossed microstructures: (1) Roughness of mold, (2) Taper angle of microstructures of mold, (3) Chemical interaction between mold and embossing, (4) Tensile and crosslinking shrinkage properties of the irradiated resin and (5) Uniformity of crosslinking process through the thickness of the molded microstructures. By controlling these five parameters, a microarray with an aspect ratio of 5 was demonstrated using a Formulation containing epoxy acrylate, Irgacure® 651, silicone acrylate and other acrylates. The embossed microstructures replicated the features of the mold very well. It was also shown that by controlling the amount of irradiation, the tensile modulus of the UV formulation increased whilst the elongation decreased. An optimum irradiation is needed for clean demolding from the mold without microcracking.This research was supported by a Strategic Development Scheme fund (SDS 15/2001) from the Nanyang Technological University. The authors also acknowledge the kind contributions of chemicals by UCB Chemicals, Sartomer, Henkel (Singapore), Dupont (Singapore) and Ciba Chemicals and a microstructured mold by Dr R. C. Liang of SiPix Imaging (CA, USA). The second author acknowledges the financial support of Nanyang Technological University through a Research Scholarship.