Cheng-Kuo Sung

Fabrication of carbon nanotube field emission cathodes in patterns by a laser transfer method

This study reports a novel approach, based on the method of laser induced pattern transfer, that can deposit patterned carbon nanotube (CNT) field emission cathodes on a variety of substrates at room temperature and in an ambient environment. Tests of emission characteristics of the fabricated cathodes present favourable emission current flux, low threshold electrical field, 1?mA?cm?2 current density at 3.3?V??m?1 for the 8??m thick film and good emission focusing. Well-defined CNT patterns with a feature size down to 10??m were produced using a mask. Compared with CNT film produced by printing based methods, higher density and better adhesion were achieved, without any post-treatment. Control of the film thickness can plainly be accomplished by adjusting the coated CNT film thickness on the support and the number of laser pulses. The fast deposition rate and high degree of feasibility of using the substrate, as well as the fabrication environment, render the proposed approach a potential method for low cost fabrication of precision patterns for CNT.

Sub-15 nm linewidth gratings using roll-to-roll nanoimprinting and plasma trimming to fabricate flexible wire-grid polarizers with low colour shift

Sub-15 nm-wide gratings with a high aspect ratio of up to 16:1 were fabricated using roll-to-roll nanoimprinting and plasma trimming to achieve high optical performance (up to 12 000:1 extinction ratio with an average transmittance of 82%) and low colour shift (transmittance variation less than 3%) flexible wire-grid polarizers for display applications. We applied two imprint platforms onto glass and plastic substrates to identify the optical properties and characteristics of each fabrication process. To enhance the tolerance, reproducibility, and optical performance of the process, the grating profile symmetry and varying residual layer thicknesses were precisely simulated and controlled to achieve the design targets.

Integrating anti-reflection and superhydrophobicity of moth-eye-like surface morphology on a large-area flexible substrate

This paper proposes an ultraviolet nanoimprint lithography (UV-NIL) roll-to-roll (R2R) process with argon and oxygen (Ar–O2) plasma ashing and coating of a dilute perfluorodecyltrichlorosilane (FDTS) layer to fabricate the large-area moth-eye-like surface morphology on a polyethylene terephthalate substrate. By using Maxwell-Garnetts effective medium theory, the optimal dimensions of the moth-eye-like surface morphology was designed and fabricated with UV-NIL R2R process to obtain maximum transmittance ratio. In addition, the base angle (θ = 30.1°) of the moth-eye-like surface morphology was modified with Ar–O2 plasma ashing and coated with a dilute FDTS layer to possess both superhydrophobic and air-retention properties. This increases both the transmittance ratio of 4% and contact angle to 153°.

Fabrication of subwavelength metallic structures by using a metal direct imprinting process

This work employs a metal direct imprinting process, which possesses the characteristics of simplicity, low-cost and high resolution, for the fabrication of subwavelength structures on a metallic thin film. Herein, the mould featuring periodic line structures is manufactured by using E-beam lithography and followed by a dry etching process; meanwhile, the thin film is fabricated by sputtering Al on a silicon substrate. AFM section analyses are employed to measure imprinting depths of the subwavelength metallic structures and it is found that the uniformity of the imprinting depths is affected by the designed patterns, the material property of thin film and mould deformation. The process temperature and the mould filling that influence the transferred quality are investigated. In addition, TEM is also utilized to examine defects in the subwavelength metallic structures. Finally, good quality subwavelength metallic structures are fabricated under a pressure of 300 MPa for 60 s at room temperature. In this study, we have demonstrated that subwavelength metallic structures with a minimum linewidth of less than 100 nm on the Al thin film are successfully constructed by the metal direct imprinting process.

Fabricating a Silver Soft Mold on a Flexible Substrate for Roll-to-Roll Nanoimprinting

This study presents an efficient method for fabricating a silver soft mold with a three-dimensional (3-D) nanostructure on flexible polyethersulfone (PES) plastic substrates for a roll-to-roll (R2R) nanoimprint process by employing hot embossing in conjunction with inkjet printing. Prior to fabricating the silver soft mold, the researchers in this study used laser interference lithography (LIL) to fabricate the silicon mold of nanopillar arrays with diameters of 146 nm, heights of 201 nm, and pitches of 291 nm. Inkjet printing was used to coat the silver nanoparticle liquid uniformly on a PES substrate with the designed drop space and volume of droplets. By using hot embossing for 210 s, the researchers transferred the nanopillar arrays from the master Si mold to the liquid on the PES substrate. Finally, the silver nanoparticles of nanohole arrays were sintered on the PES by soft baking for 6 h. The results of this study showed that the silver soft mold could effectively transfer the nanostructures to the polymer substrate through the R2R process in various applications such as antireflection devices.

Strategy for developing high efficiency backlight module for LCD

The major efficiency loss in current liquid crystal displays(LCD) are the absorption in polarizers and color filter, and both can be resolved with decent backlight design which takes light polarization and color separation into consideration. Those improvement schemes on the backlight normally will not trade off the image quality readily achieved in the commercial LCD. Both polarization and color separation schemes for the backlight are reviewed with categorization on the basic concept, followed by the proposal of possible combinations for both direct lit and edge lit configuration with the consideration on the availability of associated components. Two total solutions, including polarization conversion module for LED and pixelized backlight with RGB LED for direct lit and edge lit respectively, are given with demonstration of preliminary result achieved so far as the efficiency improvement schemes for LCD backlight.

Systematic design methodology of bistable compliant micro-mechanisms

A bistable compliant micro-mechanism possesses the distinguish characteristics of both the bistable mechanism and the compliant one. It can be suitably employed in various MEMS devices, such as a micro-relay, an impact sensor, etc. Currently, preventing fracture and enhancing reliability are the most important issues in the application of bistable compliant micro-mechanisms. Through a systematic design methodology, including tuning the parameters of geometric shapes, adding a stopper at the proper position, etc., one can obtain a more appropriate micro-mechanism for designated applications. This paper proposes a systematic methodology for the design of bistable compliant micro-mechanisms.