Jaegu Kim

Femtosecond-Laser-Coupled Near-Field Scanning Optical Microscopy Patterning Using Self-Assembled Monolayers

Investigations into the fabrication of nanoscale patterns on gold substrates via direct scanning near-field lithography were carried out. A laser beam is scanned over the workpiece where the pattern formation is desired by near-field scanning optical microscopy (NSOM). A pipette-type nanoprobe having a 100 nm aperture at its apex is used with the NSOM and a frequency-doubled Ti:sapphire femtosecond laser at a wavelength of 395 nm as the illumination source to prevent pulse dispersion of the femtosecond laser pulse. Self-assembled monolayers (SAMs) formed by the adsorption of alkanethiols onto the gold substrate are employed as very thin photoresists. The process underlying photopatterning of SAMs on gold is well-known at the phenomenological level. Alkanethiolates formed by the adsorption of alkanethiols are oxidized to alkylsulfonates upon exposure to UV light in the presence of air. Specifically, it is known that deep-UV light of wavelength less than 200 nm is necessary for oxidation to occur. The results show that an ultrafast laser can replace a deep-UV laser source for the photopatterning of thin organic films. Femtosecond-laser photolithography may be applied to create the patterning of a surface chemical structure or a three-dimensional nanostructure by combination with suitable etching methods.

Influence of tool deflection on micro channel pattern of 6：4 brass with rectangular tool

Machining experiment of micro channel structure with 6:4 brass was carried out by shaping process using a single crystal diamond tool. FEM simulation using solid cantilever beam model was analyzed. In result of experiment, tool deflection is observed as machining characteristics through result of experiments such as surface roughness, cutting force and burr formations. And the influence of tool deflection is experimentally proved.

Photothermal three-dimensional fabrication of polymers using diode-pumped solid state lasers

A layer-by-layer laser ablation process of polymers with a diode-pumped solid state (DPSS) third harmonic Nd:YVO 4 laser with wavelength of 355 nm is developed to fabricate a 3-D microshape. Polymer fabrication using DPSS lasers has some advantages compared with the conventional polymer ablation process using KrF and ArF lasers with 248 and 193 nm wavelengths, such as pumping efficiency and low maintenance fees. This method also makes it possible to fabricate 2-D patterns or 3-D shapes rapidly and cheaply because CAD/CAM software and precision stages only are used without complex projection mask techniques. The photomachinability of polymers is highly influenced by laser wavelength and its own chemical structure. So the optical characteristics of polymers for a 355-nm laser source are investigated experimentally and theoretically. The photophysical and photochemical parameters such as laser fluence, focusing position, and ambient gas are considered to reduce the plume effect, which induces the redeposited debris on the surface of a substrate. Thus, the process parameters are tuned to optimize gaining precision surface shape and quality. This direct photomachining technology using DPSS lasers could be expected to manufacture the prototype of microdevices and be the mold for the laser-LIGA process.

Design and Fabrication of a Laterally Driven Bistable Electromagnetic Microrelay

A laterally driven bistable electromagnetic microrelay has been designed, fabricated, and tested. The working principle of the proposed microrelay is based on the Flemings left hand rule. Silicon-on-insulator wafers are used for electrical isolation and releasing of the moving microstructures. The high-aspect-ratio microstructures are fabricated using a DRIE process. The tandem-typed arch- shaped leaf springs with a silicon/gold composite layer enhance the mechanical performances while reducing the electrical resistance. A permanent magnet is attached at the bottom of the silicon substrate, resulting in the generation of an external magnetic field in the vertical direction of the silicon substrate. The leaf springs show a bistable behavior. The resistance of the pair of leaf springs was 5.5Omega and the contact resistance was 4.7Omega. The driving voltage is measured to be plusmn0.5 V.

Nanoscale Patterning Using Femtosecond Laser and Self-assembled Monolayers (SAMs)

Standard positive photoresist techniques were adapted to generate nano-scale patterns of gold substrate using self-assembled monolayers (SAMs) and femtosecond laser. SAMs formed by the adsorption of alkanethiols onto gold substrate are employed as very thin photoresists, Alkanethiolates formed by the adsorption of alkanethiols are oxidized on exposure to UV light in the presence of air to alkylsulfonates. Specifically, it is known that deep UV light of wavelength less than 200nm is necessary for oxidation to occur. In this study, ultrafast laser of wavelength 800nm and pulse width 200fs is applied for photolithography. Results show that ultrafast laser of visible range wavelength can replace deep UV laser source for photo patterning using thin organic films. Femtosecond laser coupled near-field scanning optical microscopy facilitates not only the patterning of surface chemical structure, but also the creation of three-dimensional nano-scale structures by combination with suitable etching methods.

Ultrafast laser lithography using self-assembled monolayers (SAMs)

Standard positive photoresist techniques were adapted to generate micropatterns of gold substrate using self-assembled monolayers (SAMs) and ultrafast laser. SAMs formed by the adsorption of alkanethiols onto gold substrate are employed as very thin photoresists. The process underlying photopatterning of SAMs on gold is well- known at the phenomenological level. Alkanethiolates formed by the adsorption of alkanethiols are oxidized on exposure to UV light in the presence of air to alkylsulfonates. Specifically, it is known that deep UV light of wavelength less than 200nm is necessary for oxidation to occur. In this study, ultrafast laser of wavelength 800nm is applied for photolithography. Results show that ultrafast laser of visible range wavelength can replace deep UV laser source for photo patterning using thin organic films. The essential basis of our approach is the photochemical excitation of specific reactions in a particular functional group (in this case a thiolate sulfur atom) distributed with monolayer coverage on a solid surface. By using the photo-chemical process with ultrafast laser, micro-patterns with sub-micrometer width and depth on surfaces of Au could be fabricated.Standard positive photoresist techniques were adapted to generate micropatterns of gold substrate using self-assembled monolayers (SAMs) and ultrafast laser. SAMs formed by the adsorption of alkanethiols onto gold substrate are employed as very thin photoresists. The process underlying photopatterning of SAMs on gold is well- known at the phenomenological level. Alkanethiolates formed by the adsorption of alkanethiols are oxidized on exposure to UV light in the presence of air to alkylsulfonates. Specifically, it is known that deep UV light of wavelength less than 200nm is necessary for oxidation to occur. In this study, ultrafast laser of wavelength 800nm is applied for photolithography. Results show that ultrafast laser of visible range wavelength can replace deep UV laser source for photo patterning using thin organic films. The essential basis of our approach is the photochemical excitation of specific reactions in a particular functional group (in this case a thiolate sulfur atom) distributed with mo...

Micro sculpting technology using DPSSL

Multiple pulse laser ablation of polymer is performed with DPSS (Diode Pumped Solid State) 3rd harmonic Nd:YVO4 laser (355 nm) in order to fabricate three-dimensional micro components. Here we considered mechanistic aspects of the interaction between UV laser and polymer to obtain optimum process conditions for maskless photomachining using DPSSL. The photo-physical and photochemical parameters such as laser wavelength and optical characteristics of polymers are investigated by experiments to reduce plume effect, which induce the re-deposited debris on the surface of substrate. In this study, LDST (laser direct sculpting technique) are developed to gain various three-dimensional shape with size less than 500 micrometer. Main process sequences are from rapid prototyping technology such as CAD/CAM modeling of products, machining path generation, layer-by-layer machining, and so on. This method can be applied to manufacture the prototype of micro device and the polymer mould for mass production without expensive mask fabrication.

Micro-optic fabrication using laser ablation process

The feasibility of laser ablation in micro-machining of 3D structure of MEMS (Micro Electro Mechanical Systems) parts, specifically micro optics was studied in this paper. The micro-machining characteristics of polymer such as etching rate vs. energy fluence, number of pulse are investigated experimentally. The threshold energy density of polyurethane is about 30 mJ/cm2 and ablated depth per pulse can be precisely controlled in the range of 0.1-0.8μm by the attenuation of energy fluence. By mask moving technique, the micro prism, cylindrical lens and inclined surface were fabricated. These 3D structures can be used as master in electro-plating mold. This paper also summarized the work on the development of a simulation program for modeling the process of machining quasi-three dimensional shapes with the excimer laser beam on a constant moving polymer. Relatively simple masks of rectangle, triangle and half circle shape are considered. The etching depth is calculated by considering the number of laser pulses and the wavelength of laser beam irradiated on the various specimen surface such as PMMA, polyurethane and PI. It was found that similar shapes as experimental results, mask shape was designed to gain-lens surface which we want. As another method to manufacture micro lens the mask is made circular type and rotated during laser beam illumination. Opened mask area and scanning speed determine the surface shape of lens. Precise control of various parameters is admitted to fabricate micro optics.