Cheon Lee

Study on Graphene Thin Films Grown on Single Crystal Sapphire Substrates Without a Catalytic Metal Using Pulsed Laser Deposition

Copyright ©2015 KIEEME. All rights reserved. This is an open-access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0) which permits unrestricted noncommercial use, distribution, and reproduction in any medium, provided the original work is properly cited. pISSN: 1229-7607 eISSN: 2092-7592 DOI: http://dx.doi.org/10.4313/TEEM.2015.16.2.70 OAK Central: http://central.oak.go.kr

Surface modification of silicon and PTFE by laser surface treatment: improvement of wettability

Laser surface treatment was used to modify the surface of silicon and PTFE (polytetrafluoroethylene). This method is in order to improve its wettability and adhesion characteristics. Using a 4th harmonic Nd:YAG pulse laser (λ = 266 nm, pulse), we determined the wettability and the adhesion characteristics of silicon and PTFE surfaces developed by the laser irradiation. Particularly, surface treatment of PTFE was only effective when the irradiated interface was in contact with the triethylamine photoreagent. We investigated laser surface treatment of materials by the surface energy modification. By using the sessile drop technique with distilled water, we determined that the wettability of silicon and PTFE after the irradiation showed a decrease in the contact angle and a change in the surface chemical composition. In case of the laser-treated materials surface, laser direct writing of copper lines was achieved through pyrolytic decomposition of copper formate films by using a focused argon ion laser beam (λ = 514.5 nm, cw) on silicon and PTFE substrates. The deposited patterns and the surface chemical compositions were measured by using energy dispersive X-ray, scanning electron microscopy, X-ray photoelectron spectroscopy, and surface profiler to examine cross section of the deposited copper lines.

Maskless laser-induced deposition of Cu film patterns from copper formate

Laser direct writing using thin solid films of metallo- organic precursors offers some unique advantages in terms of materials design, process control, and safety over gas phase or solution processor. Micro patterned copper films were obtained by laser-induced deposition using Cu(HCOO)2 4H2O films as a precursor. Then the new applicabilities for interconnection of integrated circuits were preliminary studied by the estimation of physical and electrical properties of copper films after annealing. The growth kinetics of these Cu films was investigated as a function of the laser power and the scan speed which were varied in the range of 70 to 600 mW and 0.1 to 20 mm/s, respectively. The high-purity of the deposit was also confirmed by Auger electron spectroscopy analysis. The resistivity of the patterned copper films was a factor of about 20 higher than that of bulk value however, the resistivity decreased due to changes in morphology and porosity of the deposit and was about 10 (mu) (Omega) cm after annealing at 300 degrees C for 5 minutes.

Analysis of the Characteristics of PMSG Tidal Current Power Generation System Using PMSG and Water Tunnel

In order to analyze the characteristics of tidal current power generation system, we measured the output power according to the stream velocity by a water tunnel system and a simulation in MATLAB/Simulink. The water tunnel system consisted of impeller tidal flow transducer and permanent magnet synchronous generator (PMSG) with rotor in the water. The simulation consisted of PMSG, the tidal current turbine, and Back-to-Back converter. Also, we simulated the characteristics of output power according to the change of blade radius and velocity.

Time Dependent Inductance Calculation of Magneto-Cumulative Generator During Explosion Using Finite Element Method

The time dependent inductance variation is an essential ingredient in the design of magneto-cumulative generator. In most theoretical works, the inductance is modeled by a simple exponential form as a function of time. It is widely accepted that it is proper approximation for the time dependent inductance due to the constant expansion velocity of the liner during the explosion process. In this simple model, however, the magnetic field compression is not correctly treated. Since the inductance is related with the magnetic energy, which is determined by the magnetic flux density, the apposite consideration of the compression of the magnetic field is required. In order to include the effect of the compression of the magnetic field properly, we perform the finite element method calculation for the time dependent inductances in MCG during the explosion process. We find that the time dependent inductance can not be modeled with simple exponential model. Especially, the time derivative of the inductance shows more pronounces difference with the simple exponential model. In order to confirm the calculation results, we design mimic-explosion experiments in order to measure the inductances during the explosion process. It is revealed that the measurement data is well matched with the calculated one.

The dry laser cleaning of photoresist residues on Si and ITO substrate

The cleaning of photoresist residues on Si and ITO substrate is necessary in electronics device fabrication in order to improve the device performance and manufacturing efficiency. This study is about the laser cleaning of the photoresist residues (AZRFP23OK2) on the substrates being able to substitute conventional photoresist ashing and wet cleaning equipment. The laser cleaning effect of Q-switched Nd:YAG laser at 266 and 532 nm in order to remove the residues on Si and ITO substrate was investigated with regard to laser fluence, shots and wavelength. The cleaning efficiency for the residues on Si substrate was higher than that of ITO at the same laser fluence and shots for both 266 and 532 nm. Much more effective cleaning of the residues on the substrate can be done with flowing assistant inert N2 gas during the laser cleaning process.

Comparison of the structural characteristics and surface morphology of ZnO thin films grown on various substrates by pulsed laser deposition

ZnO thin films on (100) p-type Si and sapphire substrates have been deposited by pulsed laser deposition technique using Nd:YAG laser with a wavelength of 266 nm. The influence of the deposition parameters such as oxygen pressure, substrate temperature and laser energy density on the properties of the grown films, was studied. The experiments were performed for substrates temperature in the range of 200 - 500°C and oxygen pressure in the range of 100 to approximately 700 sccm. All the films grown in this experiment show strong c-axis orientation with (002) textured ZnO peak. With increasing substrate temperature, the full width at half maximum (FWHM) and surface roughness were descreased. In case of sapphire substrate, the intensity of PL spectra increased with increasing ambient oxygen flow rate. We investigated in the structural and morphological properties of ZnO thin films using X-ray diffraction (XRD), scanning electron microscopy (SEM) and atomic force microscopy (AFM).

Optoelectrical and optoacoustic analysis of the laser cleaning process of a photoresist on Si and ITO

By irradiating a Nd:YAG (λ=266 and 532 nm, pulse) laser beam, we investigated the cleaning process of a photoresist particles on Si and ITO substrate. The influences of laser fluence, wavelength, and substrate properties on the laser cleaning performance were investigated. The removal rate for the particles of Si substrate was higher than that of ITO at the same laser fluence and pulses for a wavelength of 266 nm. Using 2nd harmonic Nd:YAG laser (λ = 532 nm), it was found to be inappropriate for the complete particle removal and ablation of photoresist film without substrate damage. Water-condensed particles are rarely cleaned even on the laser fluence of being capable of completely removing dried sample resulting from the increase of viscosity of the particles, the scattering, and the reflection of incident laser beam.

Comparison of ITO ablation characteristics using KrF excimer laser and Nd:YAG laser

We studied to develop ITO (Indium Tin Oxide) thin films ablation with a pulsed type KrF excimer ((lambda) equals248 nm) and Nd:YAG laser ((lambda) equals262 and 532 nm) required for the electrode patterning application in flat panel display into small geometry on a large substrate area. The threshold fluence for ablating ITO on glass substrate using KrF excimer laser is about 0.1 J/cm2. In this case, through the optical microscope measurement the surface color of the ablated ITO is changed into dark brown due to increase of surface roughness and transformation of chemical composition by the laser light. And the XPS analysis showed that the relative surface concentration of Sn and In were essentially unchanged (In:Snequals5:1) after irradiating the KrF excimer laser. It has been reported that ripple like structure was by 2nd harmonic Nd:YLF laser (equals523nm). But in case of using 2nd harmonic Nd:YAG laser, in our study, the ablated films have well patterned and the shape is almost clean even though by-product exists in the vicinity of the etched surface region. But the films were damaged at the same laser fluence using 4th harmonic Nd:YAG laser. We will discuss this cause in terms of photon energy and the film thickness, used in this experiment, repetition rate and beam scan speed of each laser.

μ-BGA (ball grid array) singulation with a pulsed Nd:YAG laser

In a microelectronics industry, the (mu) -BGA singulation system has been studied by mechanical type. However, this has burr and device damage by mechanical stress. So we need to research other systems to solve many problems. There are only a few types of lasers - excimer, CO2, Nd:YAG, copper vapor lasers in use for polymers and metals. In this paper, we have studied minimization of the line-width and surface burning which occur after the singulation process with a pulsed Nd:YAG((lambda) equals532 nm, repetition rate equals10 Hz) laser. The thermal energy of a pulsed Nd:YAG laser is used to cut the copper layer. Especially, the sacrifice layer and N2 blowing are effective in minimizing surface burning. The N2 blowing reduces a laser energy loss by debris and suppresses a surface oxidation. The SEM (scanning electron microscopes), non- contact 3D inspector and high-resolution microscope are used to measure cutting line-width and surface state. The (mu) - BGA threshold energy is 234.1 kJ/cm2 at 50micrometers /s scan speed.