• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2007.10a
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• pp.758-760
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• 2007

Organic field-effect transistors (OFETs) are of interest for use in widely area electronic applications. We fabricated a copper phthalocyanine (CuPc) based field-effect transistor with different metal electrode. So we need the effect of the substituent group attached to the phthalocyanine on the surface potential was investigated by Kelvin probe method with varying temperature of the substrate. We were obtained the positive shift of the surface potential for CuPc thin film. We observed the electron displacement at the interface between Au electrode and CuPc layer and we were confirmed by the surface potential measurement.

• Journal of the Korean institute of surface engineering
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• v.29 no.6
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• pp.766-772
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• 1996

Undoped $SnO_x$ thin films were deposited on Si(100) substrate by using reactive ioassisted deposition technique (R-IAD). In order to investigate the effect of initial oxygen content and heat treatment on the oxidation state and crystalline structure of tin oxide films, $SnO_x$ thin films were post-annealed at 400~$600^{\circ}C$ for 1 hr. in a vacuum ~$5 \times 10^{-3}$ -3/ Torr or were directly deposited on the substrate of $400^{\circ}C$ and the relative arrival ration ($Gamma$) of oxygen ion to Sn metal varied from 0.025 to 0.1, i.e., average impinging energy ($E_a$) form 25 to 100 eV/atom. As $E_a$ increased, the composition ratio of $N_ON{sn}$ changed from 1.25 to 1.93 in post-annealing, treatment and 1.21 to 1.87 in in-situ substrate heating. In case of post-annealing, the oxidation from SnO to $SnO_2$ was closely related to initial oxygen contents and post-annealing temperature, and the perfect oxidation of $SnO_2$ in the film was obtained at higher than $E_a$=75 eV/atom and $600^{\circ}C$. The temperature for perfect oxidation of $SnO_2$ was reduced as low as $400^{\circ}C$ through in-situ substrate heating. The variation of the chemical state of $SnO_x$ thin films with changing $E_a$'s and heating method were also observed by Auger electron spectroscopy.

• Progress in Superconductivity
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• v.8 no.2
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• pp.181-185
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• 2007

For more than two decades Nb trilayer ($Nb/Al_2O_3/Nb$) process has been serving as the most stable fabrication process of the Josephson junction integrated circuits. Fast development of semiconductor fabrication technology has been possible with the recent advancement of the fabrication equipments. In this work, we took an advantage of advanced fabrication equipments in developing a superconducting Arithmetic Logic Unit (ALU) by using Nb trilayers. The ALU is a core element of a computer processor that performs arithmetic and logic operations on the operands in computer instruction words. We used DC magnetron sputtering technique for metal depositions and RF sputtering technique for $SiO_2$ depositions. Various dry etching techniques were used to define the Josephson junction areas and film pattering processes. Our Nb films were stress free and showed the $T{_c}'s$ of about 9 K. To enhance the step coverage of Nb films we used reverse bias powered DC magnetron sputtering technique. The fabricated 1-bit, 2-bit, and 4-bit ALU circuits were tested at a few kilo-hertz clock frequency as well as a few tens giga-hertz clock frequency, respectively. Our 1-bit ALU operated correctly at up to 40 GHz clock frequency, and the 4-bit ALU operated at up to 5 GHz clock frequency.

• Journal of the Korean Vacuum Society
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• v.6 no.1
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• pp.20-27
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• 1997

We have investigated the formation techniques of copper thin films which would be useful for sub-quarter-micron integrated circuits. A chemical vapor deposition technology has been tried for the better side wall formation of the thin films, and a metal organic compound, named (hface)Cu(VTMS) (hexafluoroacetylacetonate vinyltrimethylsilane copper(I)) was used as the precursors. We have deposited the copper thin films on TiN and $SiO_2$substrates. The film resistivity and deposition selectivity have been measured as functions of substrate temperature and chamber pressure. Best electrical properties were obtained at $180^{\circ}C$ of substrate temperature and 0.6 Torr of chamber pressure. Under the optimum deposition conditions, polycrystalline copper structures were observed to be grown, and the deposition rate of 120 nm/min was measured. The electrical resistivity as low as 0.25$mu \Omega$.cm, and the surface roughness of 15.5 nm were also measured. These are the suitable electrical and material properties required in the sub-quarter-micron device fabrication. Also, in the substrate temperature range of 140-$250^{\circ}C$, high deposition selectivity was observed between TiN and $SiO_2$.

• Tribology and Lubricants
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• v.34 no.1
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• pp.16-22
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• 2018

Cylindrical turbine guide bearings (TGBs) with simple plain pads have conventionally been used in vertical hydro-power turbine-generator applications in order to provide turbine runner shafts with smooth rotation guides and supports. To overcome low-load/low-eccentricity performance drawbacks, such as very low film stiffness and lack of design credibility in the stiffness values themselves, of conventional cylindrical TGBs, the introduction of a rotational-directional leading-edge taper to each partitioned pad, simply pad leading-edge taper, has been found to be very effective in enhancing their design-application availability and usefulness. In this study, we investigate the effects of taper angle and length for given taper heights in detail in order to systematically establish the effectiveness of design on the performance improvement of vertical hydro-power application cylindrical TGBs with pad leading-edge tapers. The analysis results with $4-Pad{\times}1-Row$ cylindrical TGBs show that the lubrication performance of the cylindrical TGBs is optimized with an approximate taper angle ratio of 0.8 and taper length ratio of 0.9. We conclude that the introduction of pad leading-edge tapers along with the optimization of taper designs can be very effective in improving the overall operation reliability of cylindrical TGBs and the rotordynamic characteristics of vertical hydro-power turbine-generator rotor-bearing systems as well, to which the TGBs are applied.

• Journal of the Korean Vacuum Society
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• v.17 no.3
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• pp.234-239
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• 2008

Tungsten and rhodium target tube for a 40 kV x-ray transmission anode was developed to apply to the hand-held XRF(X-Ray Fluorescence) apparatus and its characteristics were evaluated. From the measurement of the energy distribution and dose of x-ray, it was confirmed that our results were good agreements with the known ones. The optimum thickness of metal film deposited on Be window to extract the maximum dose were $2.6{\mu}m$ and $2.7{\mu}m$ in case of W-target tube and Rh-target tube, respectively. When it was continuously worked during 30 min. at 40 kV in tube voltage and at $60{\mu}A$ in tube current, the temperature at target did not exceed $50^{\circ}C$. Our results reveals that the 40 kV x-ray transmission anode tube can be applied to the hand-held XRF apparatus.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.167-167
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• 2011

Magnetic random access memory (MRAM) is one of the prospective semiconductor memories for next generation. It has the excellent features including nonvolatility, fast access time, unlimited read/write endurance, low operating voltage, and high storage density. MRAM consists of magnetic tunnel junction (MTJ) stack and complementary metal-oxide semiconductor (CMOS). The MTJ stack is composed of various magnetic materials, metals, and a tunneling barrier layer. For the successful realization of high density MRAM, the etching process of magnetic materials should be developed. Among various magnetic materials, FePt has been used for pinned layer of MTJ stack. The previous etch study of FePt magnetic thin films was carried out using $CH_4/O_2/NH_3$. It reported only the etch characteristics with respect to the variation of RF bias powers. In this study, the etch characteristics of FePt thin films have been investigated using an inductively coupled plasma reactive ion etcher in various etch chemistries containing $CH_4$/Ar and $CH_4/O_2/Ar$ gas mixes. TiN thin film was employed as a hard mask. FePt thin films are etched by varying the gas concentration. The etch characteristics have been investigated in terms of etch rate, etch selectivity and etch profile. Furthermore, x-ray photoelectron spectroscopy is applied to elucidate the etch mechanism of FePt thin films in $CH_4$/Ar and $CH_4/O_2/Ar$ chemistries.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.02a
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• pp.408-408
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• 2012

It is well known that magnetic random access memory (MRAM) is nonvolatile memory devices using ferromagnetic materials. MRAM has the merits such as fast access time, unlimited read/write endurance and nonvolatility. Although DRAM has many advantages containing high storage density, fast access time and low power consumption, it becomes volatile when the power is turned off. Owing to the attractive advantages of MRAM, MRAM is being spotlighted as an alternative device in the future. MRAM consists of magnetic tunnel junction (MTJ) stack and complementary metal- oxide semiconductor (CMOS). MTJ stacks are composed of various magnetic materials. FePt thin films are used as a pinned layer of MTJ stack. Up to date, an inductively coupled plasma reactive ion etching (ICPRIE) method of MTJ stacks showed better results in terms of etch rate and etch profile than any other methods such as ion milling, chemical assisted ion etching (CAIE), reactive ion etching (RIE). In order to improve etch profiles without redepositon, a better etching process of MTJ stack needs to be developed by using different etch gases and etch parameters. In this research, influences of $O_2$ gas on the etching characteristics of FePt thin films were investigated. FePt thin films were etched using ICPRIE in $CH_4/O_2/Ar$ gas mix. The etch rate and the etch selectivity were investigated in various $O_2$ concentrations. The etch profiles were studied in varying etch parameters such as coil rf power, dc-bias voltage, and gas pressure. TiN was employed as a hard mask. For observation etch profiles, field emission scanning electron microscopy (FESEM) was used.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.283-283
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• 2011

The n-doping effect by doping metal carbonate into an electron-injecting organic layer can improve the device performance by the balanced carrier injection because an electron ohmic contact between cathode and an electron-transporting layer, for example, a high current density, a high efficiency, a high luminance, and a low power consumption. In the study, first, we investigated an electron-ohmic property of electron-only device, which has a ITO/$Rb_2CO_3$-doped $C_{60}$/Al structure. Second, we examined the I-V-L characteristics of all-ohmic OLEDs, which are glass/ITO/$MoO_x$-doped NPB (25%, 5 nm)/NPB (63 nm)/$Alq_3$ (32 nm)/$Rb_2CO_3$-doped $C_{60}$(y%, 10 nm)/Al. The $MoO_x$doped NPB and $Rb_2CO_3$-doped fullerene layer were used as the hole-ohmic contact and electron-ohmic contact layer in all-ohmic OLEDs, respectively, Third, the electronic structure of the $Rb_2CO_3$-doped $C_{60}$-doped interfaces were investigated by analyzing photoemission properties, such as x-ray photoemission spectroscopy (XPS), Ultraviolet Photoemission spectroscopy (UPS), and Near-edge x-ray absorption fine structure (NEXAFS) spectroscopy, as a doping concentration at the interfaces of $Rb_2CO_3$-doped fullerene are changed. Finally, the correlation between the device performance in all ohmic devices and the interfacial property of the $Rb_2CO_3$-doped $C_{60}$ thin film was discussed with an energy band diagram.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.08a
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• pp.189-189
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• 2011

인공관절은 노인성 질환이나 자가 면역질환, 신체적인 외상 등으로 인하여 발생하는 관절의 손상 부위를 대체하기 위해 고안된 관절의 인공 대용물이다. 인공 관절 중 인공 고관절의 경우 관절 운동을 하는 라이너(Liner)와 헤드(Head) 부분이 인공관절의 수명을 결정하게 되는데, 헤드 부분에 메탈소재와 라이너 부분에 고분자 소재를 사용하는 MOP (metal on polymer) 구조의 인공관절은 충격흡수의 장점이 있는 반면 wear debris에 의한 골용해로 인하여 관절이 느슨해지는 문제점이 발생하여 재 시술의 주요 원인이 되고 있다. 또한 메탈 헤드의 마모로 인한 금속이온의 용출은 세포 독성의 문제를 야기하여 인공관절의 수명을 낮추는 또 하나의 요인이 되고 있다. 따라서 인공관절의 수명을 늘리기 위해 DLC, ZrO, TiN 등의 높은 경도 값을 갖는 박막을 금속 헤드 위에 증착하여 상대재인 인공관절용 고분자 소재의 마모량을 줄이고자 하는 연구가 활발하게 진행 되고 있다. 본 연구에서는 PIII&D (Plasma Immersion Ion Implantation & Deposition)공정을 이용하여 Co-Cr-Mo 합금 소재 niobium nitride (NbN) 박막을 증착하여 상대제인 UHMWPE (ultra high molecular polyethylene)의 마모를 줄이고자 하는 연구를 진행하였다. 마모량을 감소시키기 위하여, 박막 증착전에 질소를 이온주입하는 pre-ion implantation 공정을 도입하였으며, 또한 Co-Cr 합금과 NbN박막 사이의 접착력을 증가시키기 위하여 박막의 증착 초기에 이온주입과 증착을 동시에 수행하는 dynamic ion mixing공정을 수행하였다. NbN 박막의 특성을 평가하기 위해 XRD, XPS, AFM 등의 분석을 수행하였으며, 상대재인 초고분자량 폴리에틸렌의 마모량을 측정하기 위해 Pin-on-disk tester를 이용하여 마모 실험을 진행하였다. 마모 실험 결과, pre-ion implantation 공정을 도입한 경우 현재 상용화 되어있는 Co-Cr 합금에 비하여 마모량을 2배 이상 감소시키는 것을 확인 할 수 있었으며, dynamic ion mixing 공정을 도입한 경우 장시간의 마모 시험에 대한 마모 특성이 향상 되는 것을 확인 할 수 있었다.