UV nano embossing for polymer nano structures with non-transparent mold insert

In recent years, UV nano embossing (or imprinting) process has been widely used for mass replication of nano structures. Most of the UV embossing machines use a UV transparent mold insert (e.g. quartz or glass). However, when a master of nano structures of interest could be realized only in a UV non-transparent mold material, it would be desirable to have a UV embossing machine which could be operated with such a UV non-transparent mold insert. In this regard, we have designed and manufactured a new UV embossing system in such a way that UV non-transparent (e.g., metal or ceramic) mold inserts can also be used as the master for the mass replication of nano structures. For the new UV embossing system, we fabricate several metal mold inserts: a nickel electroformed mold insert having grating nano structures and two AAO (anodic aluminum oxide) mold inserts having dimple nano structures and high-aspect-ratio nanopores. Finally, corresponding nano structures are successfully replicated via the UV nano embossing machine developed in this study.     

SOI wafer mold with high-aspect-ratio microstructures for hot embossing process

This paper reports using a Silicon oil insulator (SOI) wafer as a mold insert for the hot embossing process on high-aspect-ratio microstructures to overcome two drawbacks of Inductive Coupled Etching (ICP) process, the area dependent etching and the micrograss. A thin sacrificial wall to eliminate the undercut in the big open area during ICP etching is also described. A good result of final embossed structure on PMMA with aspect ratio of 12 : 1, uniform thickness, and smooth surface is presented.This work is partially supported by grants NSF/LEQSF (2001-04)-RII-02, DARPA DAAD19-02-1-0338, and NASA (2002)-Stennis-22.     

Nickel stamp fabrication and hot embossing for mass-production of micro/nano combined structures using anodic aluminum oxide

Recently, “micro/nano combined structure” has attracted many researchers’ attentions due to its high potential in various research fields and applications such as biomimetics, tissue engineering, micro systems for biochemical analysis and so forth. The present paper proposes a simple and promising method for mass-production of the micro/nano combined structure, in particular, nano dimple array with micro structures with cost-effective procedures. Three major procedures of (a) master template fabrication; (b) nickel electroforming onto the master template; (c) replication by hot embossing process, are employed: the master template is fabricated by utilizing an anodic aluminium oxide (AAO) process and UV lithography technique; nickel stamp is then obtained by means of electroforming onto the master template; finally, micro/nano combined structures are moulded on a polymethyl methacrylate (PMMA) substrate using the nickel stamp via hot embossing. So replicated micro/nano combined structures turns out to be quite successful according to experimental observation via scanning electron microscope (SEM) and atomic force microscope (AFM).     

Replication of nanostructures on microstructures by intermediate film mold inserted hot embossing process

The present study proposes a simple method to replicate nano/micro combined multiscale structures using an intermediate film mold and anodic aluminum oxide (AAO) nanomold in hot embossing process. The proposed method is simply to add an intermediate film mold with microscale thru-hole patterns to the ordinary mold system, on which nanostructures are patterned, in the hot embossing process. The intermediate film mold is inserted between polymer substrate and AAO nanomold. During the hot embossing process, the polymer first fills microscale thru-hole patterns in the intermediate film mold and subsequently fills nanopores in AAO nanomold, resulting in the nano/micro combined structures. The intermediate film molds, which have microscale thru-hole patterns were fabricated by micro-milling, laser ablation, etching methods and/or LIGA process. The nano/micro combined structures were successfully replicated by the proposed method.     

Fabrication of high-aspect-ratio electrode array by combining UV-LIGA with micro electro-discharge machining

In this paper, the combination of UV-LIGA with the Micro electro-discharge machining (Micro-EDM) process was investigated to fabricate high-aspect-ratio electrode array, and an easy and rapid process for fabricating ultra-thick SU-8 microstructures up to millimeter depth was described. First, the modified UV-LIGA process was used to fabricate the copper hole array, and then the hole array electrode was employed as a tool in the Micro-EDM process to fabricate the multiple-tipped electrodes. Electrode array of various shapes have been fabricated by this technique. The aspect ratio is up to 17.65.     

Large area micro hot embossing of Pyrex glass with GC mold machined by dicing

Micro/Nano imprinting or hot embossing is currently a target of interest for industrial production of micro and Nano devices for the low cost aspect. In Fluidic MEMS (Micro Electromechanical Systems) applications, polymer materials have been widely employed for their low cost to fabricate the economical products (Becker and Heim in Sens Acuators A 83:120–135, 2000; Becker and Gaertner in Mol Biotechnol 82:89–99, 2001). However glasses are much more suitable for the higher temperature applications or under the stronger chemical environments. Moreover UV absorption of glass materials is much less than that of polymers, which is the advantage for bio-analysis. In Optical MEMS as well, glasses are good candidate materials for the better optical properties, such as high refractive index, low UV absorption and others. Although wet etching of glasses is widely employed for fabrication of fluidic MEMS devices, the wet etching is not satisfactory for the low machining resolution, the isotropic etched profile and poor roughness of the fabricated structures. Dry etching of glasses is then an alternative for Micro/Nano structuring, but the etching rate is extremely low (order of 0.1 μm/min) and the cost is too high because of the expensive RIE (Reactive Ion Etching) facility. Above mentioned is the reason why we are interested in hot embossing or imprinting of glasses of Micro/Nano scale. In our previous study, Micro/Nano imprinting was developed for Pyrex glasses using GC (Glassy Carbon) mold prepared by FIB machining (Takahashi et al. in Symposium on DTIP 2004 pp 441–446, 2004). The disadvantage of FIB machining is limited area of etching. The typical area of FIB is less than several hundreds micrometer square. This is the reason why we tried the large area of embossing using GC mold fabricated by dicing machine. Micro hot embossed test structures were successfully demonstrated with good fidelity. Fabricated micro structures can be applied for fabrication of microchamber array for PCR (Akagi et al. in Sci Techol Adv Mater 5:343–349, 2004; Nagai et al. in Anal Chem 73:1043–1047, 2001).     

On characteristics of pore size distribution in hybrid pulse anodized high-aspect-ratio aluminum oxide with Taguchi method

Many anodic aluminum oxide (AAO) templates were traditionally performed by potentiostatic anodization at 0–10 °C to inhibit the Joule’s heat enhanced dissolution in aluminum oxide for ordered AAO configuration. In this article, the hybrid pulse anodization has been performed for offering the effective suppression of Joule’s heat generation in high-aspect-ratio AAO formation at room temperature. The effect of pulse period, duty ratio, potential and electrolytic concentration on the evolution of pore characteristics was investigated using Taguchi method. The AAO morphology was captured by scanning electron microscope, and analyzed by gray-scale imaging in order to identify the pore size distribution and AAO thickness for Taguchi analysis. Short pulse-off period and low current density improved the uniformity of pore distribution. Moreover, high current density and intermediate pulse period/duty ratio can enhance the reaction rate and resulted in thick AAO. The evolution of AAO configuration and thickness were further correlated and discussed with pulse modulations and electrolytic concentrations.     

Fabrication of porous anodic aluminum oxide by hybrid pulse anodization at relatively high potential

Anodic aluminum oxide (AAO) containing high-aspect ratio pore channels has been widely used as a template for fabricating nanowires or other 1D nanostructures. For AAO prepared in oxalic acid, the anodizing potential is set as 40 V in order to balance the oxidation and dissolution rates. In practice, a higher potential is beneficial in increasing the pore size. However, a higher potential increases the local electrolyte temperature and therefore damages the pore structure. In this article, this problem is resolved by means of a high-potential hybrid pulse anodization (HPA) technique, in which a period of small negative potential is applied to suppress the Joule heating effect during the AAO preparation process. The scanning electron microscope results showed that HPA with an anodizing potential of 60 V resulted in an intact pore structure on the AAO surface. By contrast, the AAO formed using conventional direct current anodization with the same anodizing potential contained many small irregular pores around each original pore. The present results suggest that HPA has significant potential for the fabrication of high-quality nanowires with various diameters for such applications as magnetic recording, super capacitors or field emission devices.     

Development of an UV rolling system for fabrication of micro/nano structure on polymeric films using a gas-roller-sustained seamless PDMS mold

Microsystem Technologies - Roller imprinting is one of the most effective methods to fabricate polymeric plate components with nanostructures on the surface. In this study, a gas-bag roller is...     

Replication of large scale micro pillar array with different diameters by micro injection molding

The capillary force is always used as the driving force of microfluidic chips. In this study, the capillary force of blood smart diagnostic microfluidic chip which fabricated by micro-injection molding (μ-IM) is offered by the structure of micro pillar array. And the detection effect of blood smart diagnostic microfluidic chips is affected by the replication and height distribution of large scale micro pillar array. So the effect of process parameters on the micro-structure and the height distribution of micro pillar is studied. The mold design is also an important factor affecting micro parts properties. In this study, a steel mold insert with almost 15,500 micro blind cavities was fabricated by milling, electrical discharge machine and Femtosecond Laser process. Polymethyl methacrylate -Polystyrene copolymer (SMMA NAS 30) was used as the molding material. The single factor trail and orthogonal experiment approach were adopted to investigate the effect of several process parameters and the significant effect factors affecting the replication of micro pillar. And the height distribution of micro pillar array was investigated by scanning electron microscope (SEM) and universal tool-measuring microscope to measure the replication quality. The results reveal that the replication of micro pillar is sensitive to the flow direction of the polymer melt. The height of micro pillar increases with the increase of mold temperature and injection speed. Moreover, the height distribution of micro pillar along and against flow direction was tightly related to the thermomechanical history of material during the molding process.