We have developed a direct conductive patterning method with micro-scale line widths using the laser-induced-forward transfer (LIFT) and liquid metal. As this method does not need post-thermal processing, there is no thermal damage even on heat-sensitive polymer substrates by low-power laser irradiation on the dynamic release layer (DRL). Unlike other liquid metal patterning processes, this procedure can easily achieve fine line widths of a few tens of micrometers corresponding to laser spot size. The solid-state UV pulse laser with 266 nm wavelength and 20 ns pulse duration was used to transfer Eutectic Gallium Indium (EGaIn) liquid metal and the results for the single and multi-pulse laser irradiation were investigated to determine the effective process conditions. The applicability of flexible circuit fabrication and selective circuit repair was successfully tested on Polyimide (PI) substrate. After the LIFT process, the electrical properties of liquid metal on the pattern were measured to be approximately 5~8 x 10^-3 Ω/m of resistance.

In this study, a digital mask-based STED lithography technique was proposed, and the effective resolution of the proposed system was calculated analytically. The proposed STED lithography system uses two spatial light modulators to modulate the phase of an excitation beam and a depletion beam, respectively. The excitation spatial light modulator acts as a digital mask to form the patterning image, while the depletion spatial light modulator creates an image surrounding the projected excitation image. Thus, photopolymerization is suppressed by stimulated emission occurring in the depletion focus region surrounding the excitation focus, thereby improving lithographic resolution. Electromagnetic field and intensity distribution were calculated, and the resolution of the proposed STED lithography was simulated based on vectorial diffraction theory. An effective resolution of 72 nm was calculated under the condition of I_s 0.1, which is similar to the resolution of conventional STED lithography at 70 nm. These results analytically confirmed that the proposed STED lithography system could pattern a two-dimensional region simultaneously without the loss of resolution compared to conventional STED lithography.

With the progress of flexible devices, numerous researchers aim to manufacture the flexible battery with freefrom at various scales. Laser cutting is considered as one of the essential processes to achieve on-demand manufacturing but continuous wave or long-pulse laser beam may cause large heat affect zone (HAZ) in cutting edge and may even result in failure of battery function. Herein, it was demonstrated that the sophisticated cutting process using ultra-short pulse laser is applicable for tailoring of flexible battery with multilayered structure. Based on the comparison of cutting results using nanosecond laser and femtosecond laser, we confirmed that laser cutting by femtosecond laser induces much less thermal damage on thin foil electrodes, separator, and electrolyte. Furthermore, we investigated the interaction of femtosecond laser with the materials composed of a flexible battery and implemented a process for cutting each material without causing any critical damage. To prevent a short circuit between the anode and cathode, which usually occurs during laser cutting of the actual battery, the double-side cutting process was done by adjusting the focal points of the laser beam. We assume that the proposed approach can be applied in a roll-to-roll based cutting process for the mass-production of flexible devices.

Chemical vapor deposition (CVD) is one of the various synthesis methods that have been employed for carbon nanotube (CNT) growth. In particular, Ren et al reported that large areas of vertically aligned multi-wall carbon nanotubes could be grown using plasma-enhanced chemical vapor deposition (PECVD). In this study, we synthesized aligned CNT arrays using a direct current (dc) PECVD system. The synthesis of CNT requires a metal catalyst layer, etchant gas, and a carbon source. In this work, the substrates consisted of Si wafers with Ni-deposited film. Ammonia (NH3) and acetylene (C2H2) were used as the etch ant gases and carbon source, respectively. Pretreated conditions had an influence on vertical growth and density of CNTs. And patterned growth of CNTs could be achieved by lithographical defining the Ni catalyst prior to growth. The length of single CNT was increased as nickel dot size increased, but the growth rate was reduced when nikel dot size was more than 200 nm due to the synthesis of several CNTs on single Ni dot. The morphology of the carbon nanotubes by TEM showed that vertical CNTs were multi-wall and tip-type growth mode structure in which a Ni cap was at the end of the CNT.

Photochemical patterning of self-assembled mono layers (SAMs) has been performed by diode pumped solid state (DPSS) 3rd harmonic Nd:YV04 laser with wavelength of 355 nm. SAMs patternings of parallel lines have subsequently been used either to generate compositional chemical patterns or fabricate microstructures by a wet etching. This paper describes a selective etching process with patterned SAMs of alkanetiolate molecules on the surface of gold. SAMs formed by the adsorption ofalkanethiols onto gold substrate employs as very thin photoresists. In this paper, the influence of the interaction between the functional group of SAMs and the etching solution is studied with optimal laser irradiation conditions. The results show that hydrophobic functional groups of SAMs are more effective for selective chemical etching than the hydrophilic ones.

Transparent materials are widely used in the fields of optic parts and bio industry. We have experiment to find out the characteristics of the micro machining inside transparent materials using femtosecond laser pulses. With its non-linear effects by very high peak intensity, filament (plasma channel) was formed by the cause of the self-focusing and the self-defocusing. Physical damage could be found when the intensity is high enough to give rise to the thermal stress or evaporation. At the vicinity of the power which makes the visible damage or modification, the structural modification occurs with the slow scanning speed. According to the polarization direction to the scanning direction, the filament quality is quite different. There is a good quality when the polarization direction is parallel to the scanning direction. For fine filament, we could suggest the conditions of the high numerical aperture lens, the short shift of focusing point, the low scanning speed and the low power below 20 ㎽. As the examples of optics parts, we fabricated the fresnel zone plate with the 225 ㎛ diameter and Y-bend optical wave guide with the 5㎛ width.

An experimental study of the femtosecond laser machining of Si materials was carried out. Direct laser machining of the materials for the feature size of a few micron scale has the advantage of low cost and simple process comparing to the semiconductor process, E-beam lithography, ECM and other machining process. Further, the femtosecond laser is the better tool to machine the micro parts due to its characteristics of minimizing the heat affected zone(HAZ). As a result of line cutting of Si, the optimal condition had the region of the effective energy of 2mJ/㎜-2.5mJ/㎜ with the power of 0.5㎽-1.5㎽. The polarization effects of the incident beam existed in the machining qualities, therefore the sample motion should be perpendicular to the projection of the electric vector. We also observed the periodic ripple patterns which come out in condition of the pulse overlap with the threshold energy. Finally, we could machined the groove with the linewidth of below 2 ㎛ for the application of MEMS device repairing, scribing and arbitrary patterning.