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이석,김상훈,라현욱,한윤봉 한국화학공학회 2007 화학공학의이론과응용 Vol.10 No.2
ZnO films deposited on ZnO homo-buffer layer with different thicknesses were successfully prepared by atomic layer deposition. This two-step growth technique using homo-buffer layer is necessary to overcome the negative effects caused by hetero-buffer layer and lattice, thermal mismatch between ZnO and silicon. Crystallinity of ZnO films was characterized by X-ray diffractometer. FWHM of ZnO (002) peak is decreased with buffer layer thickness up to 327A. Surface morphology is also observed by scanning electron microscope (SEM). When the thickness of buffer layer is 327A, it shows mirror-like surface. The photoluminescence (PL) spectra show a strong UV emission at near 380nm. However, defect-related visible band also appears at all samples. The intensity ratio of the UV band to the visible band is largest at sample (c) with 327A buffer. The above results indicate that the optimum buffer layer thickness to improve the ZnO film quality is 327A.
P-842 : High Density Plasma Etching of Hard Mask Materials of SiO2, α-C:H, and ZnO
라현욱,옥치원,이석,김상훈,한윤봉 한국화학공학회 2007 화학공학의이론과응용 Vol.10 No.2
Due to the degradation of photoresists before the considerable depth and wide of etching of the substrate in the etch process, the photoresist cannot be used for a high aspect ratio etching process. Therefore, hard mask was widely used as an etch mask because of the high plasma resistant to achieve a considerable aspect ratio. This work contains the comparison of SiO2, α-C:H, and ZnO as hard mask materials for high density plasma etching of silicon in CF4/Ar discharges. The mask erosion and etch profile were affected by the processing parameters such as ICP source power, rf chuck power, operating pressure, and etch gas concentration. ZnO is the best, which fulfills the requirement of stable hard mask materials for CF4/Ar inductively coupled plasmas employed for silicon etching. While, α-C:H and SiO2 were eroded exposure to CF4/Ar inductively coupled plasmas.
P-499 : Heat Transfer Analysis of High Power LED packages
라현욱,옥치원,이석,김상훈,한윤봉 한국화학공학회 2007 화학공학의이론과응용 Vol.10 No.2
Light emitting diodes (LEDs) conventionally have been used for indicators. The introduction of high brightness LEDs with white light and monochromatic colors have led to a movement towards specialty and general illumination applications. The increased electrical currents used to drive the LEDs have focused more attention on the thermal managements of LED power packaging due to the efficiency and reliability of LEDs strictly depend on the junction temperature. In this work, we calculated the temperature distribution of LED power packaging as a function of input currents, used materials, and package geometry for a thermal design of high power LED. The temperature of high power LED package increased with the input current, particularly in glass silicon and epoxy resins. The temperature of high power LEDs package decreases with the thermal conductivity of thermal paste and heat slug size. The decrease in temperature is explained by increasing the heat flux through heat slug and heat conduction.
P-846 : Structural and optical properties of ZnO nanoparticles grown by atomic layer deposition
이석,( Ahmad Umar ),임용환,김상훈,라현욱,한윤봉 한국화학공학회 2007 화학공학의이론과응용 Vol.10 No.2
The high crystallinity and high density ZnO nanoparticles have been successfully grown over a Si(100) using 10 nm thin film of Au, which act as a catalyst, on the substrate by a novel atomic layer deposition (ALD) method at a low temperature (500℃) in which diethyl zinc and oxygen gas were used as a source of Zn and oxygen, respectively. The FESEM images of the grown nanoparticles shows that the average sizes of the particles are in the range of 10- 30 nm. X-ray diffraction data shows that the grown structures are wurtzite hexagonal and preferentially oriented in the c-axis direction. Three peaks have been observed in the PL spectra, at 378nm, 520nm and 577nm assigned to be as UV emission and green emission (520nm and 577nm). The strong UV emission and weak green emission in the PL spectra shows that as grown, low temperature ZnO nanoparticles have a good crystal quality with very less oxygen vacancies.
E-23 : Structural and optical properties of flower and needle-shaped ZnO nanostructures by ALD
( Umar Ahmad ),이석,김상훈,라현욱,한윤봉 한국화학공학회 2007 화학공학의이론과응용 Vol.10 No.2
A novel method, atomic layer deposition is employed to grow the needle and flower-shaped ZnO arrays at different growth temperatures. The needle shaped nanostructures were grown on the Au catalyzed Si(100) substrate while the flower-shaped was grown without metal catalyst on Si(100) substrate. The high density needle-shaped ZnO nanostructures were confirmed using the field emission electron microscopy. Investigations using the high resolution transmission electron microscopy and selected area electron diffraction patterns confirmed that the as-grown nanostructures are single crystalline with wurtzite hexagonal structure and preferentially oriented in the c-axis direction. Optical properties of these structures were measured at room temperature by photoluminescence spectroscopy. The needle-shaped and flower shaped nanostructures show a broad band in the visible region with suppressed UV emission. It is indicating that these nanostructures have structural defects (oxygen vacancies and zinc interstitials etc).