A Surface Etching for Synthetic Diamonds with Nano-Thick Ni Films and Low Temperature Annealing

Song, Jeongho,Noh, Yunyoung,Song, Ohsung The Korean Ceramic Society 2015 한국세라믹학회지 Vol.52 No.4

Ni (100 nm thick) was deposited onto synthesized diamonds to fabricate etched diamonds. Next, those diamonds were annealed at varying temperatures ($400{\sim}1200^{\circ}C$) for 30 minutes and then immersed in 30 wt% $HNO_3$ to remove the Ni layers. The etched properties of the diamonds were examined with FE-SEM, micro-Raman, and VSM. The FE-SEM results showed that the Ni agglomerated at a low annealing temperature (${\sim}400^{\circ}C$), and self-aligned hemisphere dots formed at an annealing temperature of $800^{\circ}C$. Those dots became smaller with a bimodal distribution as the annealing temperature increased. After stripping the Ni layers, etch pits and trigons formed with annealing temperatures above $400^{\circ}C$ on the surface of the diamonds. However, surface graphite layers existed above $1000^{\circ}C$. The B-H loop results showed that the coercivity of the samples increased to 320 Oe (from 37 Oe) when the annealing temperature increased to $600^{\circ}C$ and then, decreased to 150 Oe with elevated annealing temperatures. This result indicates that the coercivity was affected by magnetic domain pinning at temperatures below $600^{\circ}C$ and single domain behavior at elevated temperatures above $800^{\circ}C$ consistent with the microstructure results. Thus, the results of this study show that the surface of diamonds can be etched.

Color Evolution in Single Crystal Colored Cubic Zirconias With Annealing Atmosphere and Temperature

Song, Jeongho,Noh, Yunyoung,Song, Ohsung The Korean Ceramic Society 2016 한국세라믹학회지 Vol.53 No.4

Color change in single-crystal, yellow, red, purple, and colorless cubic zirconias (CZs) was investigated as a function of annealing in vacuum and air atmosphere at $800-1400^{\circ}C$ for 30 min, for development of a damascene process of plugging a precious metal paste at the elevated temperature. Coloring-element contents of the CZs were evaluated using WD-XRF, and the color change determined visually by naked eye, and using a digital camera and UV-Vis-NIR color analyzer. WD-XRF showed that all of the CZs had cubic-phase stabilizer elements and coloring elements. All CZs that underwent vacuum annealing exhibited a slight color change at $<900^{\circ}C$, while their colors began to change to black at $1100^{\circ}C$, and became opaque black at $1400^{\circ}C$. After air annealing, there was almost no color change up to $1400^{\circ}C$. Since red and purple CZs showed greater color difference (CD) values than the others, the degree of CD is likely to depend on the original color of the CZ due to the different stabilities of their coloring elements during annealing. Based on our results, it is suggested that annealing in air at $<900^{\circ}C$ is advantageous, and assorted colored CZs can be used for precious metal damascene.

Properties of Iridium-Inserted Nickel Silicides by Thermal Annealing of the Ni/Ir bilayer on Silicon and Polysilicon Substrates

( Ohsung Song ),( Kijeong Yoon ) 대한금속재료학회 ( 구 대한금속학회 ) 2007 METALS AND MATERIALS International Vol.13 No.3

To improve the thermal stability of the conventional nickel monosilicide, 10 nm-Ni/1 nm-Ir/p-Si(100)(or polycrystalline Si) was thermally annealed using rapid thermal annealing for 40 s at 300-1200 oC. The annealed bilayer structure developed into Ni(Ir)Si, and the resulting changes in sheet resistance, microstructure, and composition were investigated using a four-point probe, a scanning electron microscope, a field ion beam, an X-ray diffractometer, and an Auger electron spectroscope. The final thickness of Ni(Ir)Six formed on single crystal silicon was approximately 40 nm, and it maintained a sheet resistance of below 20 Ω/sq. during the silicidation annealing at 1200 oC. The silicide formed on polysilicon had a thickness of 55 nm, and its low resistance was maintained up to 850 oC. An additional annealing of silicides at 900 oC for 30 min. resulted in a drastic increase in sheet resistance. A possible reason for the improved thermal stability of the silicides formed on single crystal silicon substrate is the role of iridium in preventing NiSi2 transformation. Iridium also improved the thermal stability of the silicides formed on the polysilicon gate, but this enhancement was lessened due to the formation of NiIrSix and also as a result of silicon mixing during high temperature diffusion. In conclusion, the proposed iridium-inserted nickel silicides may be superior to the conventional nickel monosilicides due to improved thermal stability.

VOID DEFECTS IN COBALT-DISILICIDE FOR LOGIC DEVICES

Ohsung Song,Youngsook Ahn 한국표면공학회 1999 한국표면공학회지 Vol.32 No.3

Properties of Polysiloxane Coated Borosilicate Lining Blocks

Song, Jeongho,Song, Ohsung The Korean Ceramic Society 2017 한국세라믹학회지 Vol.54 No.6

To improve the thermal resistance of a porous borosilicate lining block, we prepared and applied polysiloxane-fumed silica-ethanol slurry on top of the block and fired the coating layer using a torch for 5 minutes at $800^{\circ}C$. We conducted magnified characterizations using a microscope and XRD analysis to observe phase transformations, and TGA-DTA analysis to determine the thermal resistance. Thermal characterizations showed improved heat resistance with relatively high polysiloxane content slurry. Cross-sectional optical microscope observation showed less melting near the surface and decreased pore formation area with higher polysiloxane content slurry. XRD analysis revealed that the block and coating layer were amorphous phases. TGA-DTA analysis showed an endothermic reaction at around $550^{\circ}C$ as the polysiloxane in the coating layer reacted to form SiOC. Therefore, coating polysiloxane on a borosilicate block contributes to preventing the melting of the block at temperatures above $800^{\circ}C$.

Magnetoresistance and Strain in Permalloy Films

Ohsung Song,Yasushi Maeda 한국자기학회 1998 Journal of Magnetics Vol.3 No.1

We measured the magnetoresistance (MR) of sputtered Permalloy (Ni_(83)Fe_(17)) films with external strains produced by piezoelectric transducer actuators. We observe that the MR ratio was increased by 2.3 times by a compressive strain of 3.5×10-⁴ compared to that of the as-deposited film. Tensile strains and compressive strains reduced the MR ratio. These observations suggest that it is possible to tune the MR properties through the use of the external strains. We expect to apply the results for the multi-head magnetic recorders with selectively activated recording heads.

Tunnel Magnetoresistance with Plasma Oxidation Time in Doubly Oxidized Barrier Process

Song, Ohsung,Lee, Y.M.,Lee, Kiyung,Yoon, C.S.,Kim, C.K. 대한금속재료학회 2003 METALS AND MATERIALS International Vol.9 No.4

Magnetic tunnel junctions (MTJ) with the tunnel barrier oxidized in tyo steps with plasma were fabricated to obtain a structurally unifomi AlO_(x), insulator. Plasma oxidation of 10 Å-thick Al layer for 5-20 sec formed the initial oxide barrier on top of which a second oxide layer was deposited by oxidizing 13 Å-thick A1 for 120 sec. The doubly oxidized junctions exhibited a magnetoresistance (MR) ratio of 27-31 % depending on the oxidation period of the initial oxide layer while only 24 % was obtained for the junction deposited in one-step oxidation with a similar stack configuration. The junction resistance of the MTJ increased mono- tonically with oxidation time while minimal deterioration of the MR ratio was observed when oxidation time increased from 5 sec to 20 sec. Transmission electron microscopy of the junctions also confirmed that the AlO, thickness was thinner for the doubly oxidized junctions compared to the singly oxidized MTJ. X-ray photoelectron spectroscopy of the double junction also strongly suggested that the initial oxide layer prevents over-oxidation of the bottom electrode. Our results suggest that the AlO_(x) oxidized in two steps produces improved junction performance as well as a wider processing window.

Properties of the Green Gold Alloys with Indium Content

Song, Jeongho,Song, Ohsung Materials Research Society of Korea 2018 한국재료학회지 Vol.28 No.4

The property changes of 18, 14, and 8K green gold alloys for jewelry are observed by adding 0.0, 3.0, and 5.0 wt% of indium (In), respectively. To check the composition of the alloys, an energy dispersive spectroscopy (EDS) analysis is conducted. Color and microstructure analysis is executed through bare-eye, macro camera, UV-VIS-NIR-colormeter, and optical microscope. The melting point, wetting angle, and hardness are measured using TGA-DTA, a wetting angle tester, and a Vickers hardness tester. The EDS analysis result demonstrates that each of the green gold alloys was manufactured with purposed contents. The color analysis result shows that the color of the alloys is similar to the color of the conventional 4 wt%-Cd 18K green gold, and the green color improves as the In content increases. The micro structure analysis result demonstrates that grain refinement improves as the amount of In increases. Enhancements in the melting point, wettability, and Vickers hardness changes appear as the In content increases and Au content decreases. The hardness is up to 260, which implies good durability. Therefore, the results suggest that the proposed 18, 14, and 8K In-added green gold alloys enhance the properties of jewelry products with regard to the green color, castability, and durability.

Direct Bonding of Silicon Pairs with Heterogeneous Insulator Using Different Annealing Methods

Song, Ohsung,Lee, Kiyung,Yoon, C.S.,Kim, C.K. 대한금속재료학회 2004 METALS AND MATERIALS International Vol.10 No.1

We prepared SO1 (silicon-on-insulator) wafer pairs of 2000 Å - SiOdSi(l00) and 560 Å- Si₃N₄/Si(l00) by CFA (Conventional electric Furnace Annealing), RTA (Rapid Thermal Annealing), and FLA (Fast Linear Annealing) at different annealing temperatures for each annealing process. We measured the bonding area and the bonding strength for the respective processes. It was demonstrated that the measured bonding area was close to 100 % above 450 ℃ for RTA, y d 400℃ for CFA. The maximum bond strength of the SiO₂/Si₃N₄ wafer pair was 2344, 2300, and 195 mJ/㎡ for CFA, FLA, and RTA, respectively. We clearly demonstrated that the FLA method is far superior in producing high-quality directly bonded Si wafer pairs with SiO₂ and Si3N4films compared to the CFA and RTA methods.

Color Enhancement of Natural Sapphires by High Pressure High Temperature Process

Song, Jeongho,Noh, Yunyoung,Song, Ohsung The Korean Ceramic Society 2015 한국세라믹학회지 Vol.52 No.2

We employed the high-pressure high temperature (HPHT) process to enhance the colors of natural sapphires to obtain a vivid blue. First, we analyze the content of the coloring agent $Fe_2O_3$ using the wavelength dispersive X-ray fluorescence (WD-XRF) method. The HPHT procedure operates under 1 GPa at various temperatures of 1700, 1750, and $1800^{\circ}C$ for 5 minutes using a cubic press. We determine the color changes using the optical microscopic images, UV-VIS near-infrared (NIR) spectra, micro-Raman spectra, and Fourier transform-infrared (FT-IR) spectra for all sapphire samples before and after the treatment. The optical microscopic results indicate that the HPHT process can enhance the sapphire color to a vivid blue at temperatures above $1750^{\circ}C$. The UV-VIS-NIR spectra identify the color changes explicitly and quantitatively through providing the Lab color scales and color differences. Both results demonstrate that the colors of natural sapphires can be enhanced to a vivid blue using the HPHT process above $1750^{\circ}C$ under 1 GPa for 5 minutes.