• Journal of the Korean Ceramic Society
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• v.35 no.7
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• pp.647-647
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• 1998

(La,Sr)CoO3/Pb(Zr,Ti)O3/(La,Sr)CoO3 (LSCO) heterostructures have been grown on LaAlO3 substrates by pulsed laser deposition (PLD) to investigate asymmetric polarization of Pb(Zr,Ti)O3 (PZT) thin flims with different electrode configuration. P-V hysteresis loop of LSCO/PZT/LSCO was symmetric. However, LaCoO3 (LCO_/PZT/LSCO showed a largely asymmetric P-V hystersis loop and large relaxation of the remanent polarization at the negatively poled state, which means that the negatively poled state was unstable. On the other hand, LSCO/PZT/LCO exhibited large relaxation of the positively poled state. The asymmetric behavior of the polarized states implies the presence of an interal electric firld inside the PZT layer. It is suggested that internal electric field is caused by built-in voltages at LCO/PZT and LSCO/PZT interfaces. The built-in voltages at LCO/PZT and CSCO/PZT interfaces were 0.6 V and -0.12 V, respectively.

• Proceedings of the Korean Vacuum Society Conference
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• 2000.02a
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• pp.186-186
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• 2000

After LeComber et al. reported the first amorphous hydrogenated silicon (a-Si: H) TFT, many laboratories started the development of an active matrix LCDs using a-Si:H TFTs formed on glass substrate. With increasing the display area and pixel density of TFT-LCD, however, high mobility TFTs are required for pixel driver of TF-LCD in order to shorten the charging time of the pixel electrodes. The most important of these drawbacks is a-Si's electron mobiliy, which is the speed at which electrons can move through each transistor. The problem of low carier mobility for the a-Si:H TFTs can be overcome by introducing polycrystalline silicon (poly-Si) thin film instead of a-Si:H as a semiconductor layer of TFTs. Therefore, poly-Si has gained increasing interest and has been investigated by many researchers. Recnetly, fabrication of such poly-Si TFT-LCD panels with VGA pixel size and monolithic drivers has been reported, . Especially, fabricating poly-Si TFTs at a temperature mach lower than the strain point of glass is needed in order to have high mobility TFTs on large-size glass substrate, and the monolithic drivers will reduce the cost of TFT-LCDs. The conventional methods to fabricate poly-Si films are low pressure chemical vapor deposition (LPCVD0 as well as solid phase crystallization (SPC), pulsed rapid thermal annealing(PRTA), and eximer laser annealing (ELA). However, these methods have some disadvantages such as high deposition temperature over $600^{\circ}C$, small grain size (<50nm), poor crystallinity, and high grain boundary states. Therefore the low temperature and large area processes using a cheap glass substrate are impossible because of high temperature process. In this study, therefore, we have deposited poly-Si thin films on si(100) and glass substrates at growth temperature of below 40$0^{\circ}C$ using newly developed high rate magnetron sputtering method. To improve the sputtering yield and the growth rate, a high power (10~30 W/cm2) sputtering source with unbalanced magnetron and Si ion extraction grid was designed and constructed based on the results of computer simulation. The maximum deposition rate could be reached to be 0.35$\mu$m/min due to a high ion bombardment. This is 5 times higher than that of conventional sputtering method, and the sputtering yield was also increased up to 80%. The best film was obtained on Si(100) using Si ion extraction grid under 9.0$\times$10-3Torr of working pressure and 11 W/cm2 of the target power density. The electron mobility of the poly-si film grown on Si(100) at 40$0^{\circ}C$ with ion extraction grid shows 96 cm2/V sec. During sputtering, moreover, the characteristics of si source were also analyzed with in situ Langmuir probe method and optical emission spectroscopy.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.36 no.9
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• pp.931-935
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• 2012

In this study, we fabricate and investigate low-temperature solid oxide fuel cells with a ceramic substrate/porous metal/ceramic/porous metal structure. To realize low-temperature operation in solid oxide fuel cells, the membrane should be fabricated to have a thickness of the order of a few hundreds nanometers to minimize IR loss. Yttrium-doped barium zirconate (BYZ), a proton conductor, was used as the electrolyte. We deposited a 350-nm-thick Pt (anode) layer on a porous substrate by sputter deposition. We also deposited a 1-${\mu}m$-thick BYZ layer on the Pt anode using pulsed laser deposition (PLD). Finally, we deposited a 200-nm-thick Pt (cathode) layer on the BYZ electrolyte by sputter deposition. The open circuit voltage (OCV) is 0.806 V, and the maximum power density is 11.9 mW/$cm^2$ at $350^{\circ}C$. Even though a fully dense electrolyte is deposited via PLD, a cross-sectional transmission electron microscopy (TEM) image reveals many voids and defects.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.200-200
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• 2010

In recent times, metal oxide semiconductors thin films transistor (TFT), such as zinc and indium based oxide TFTs, have attracted considerable attention because of their several advantageous electrical and optical properties. There are many deposition methods for fabrication of ZnO-based materials such as chemical vapor deposition, RF/DC sputtering and pulsed laser deposition. However, these vacuum process require expensive equipment and result in high manufacturing costs. Also, the methods is difficult to fabricate various multicomponent oxide semiconductor. Recently, several groups report solution processed metal oxide TFTs for low cost and non vacuum process. In this study, we have newly developed solution-processed TFTs based on Ti-related multi-component transparent oxide, i. e., InTiO as the active layer. We propose new multicomponent oxide, Titanium indium oxide(TiInO), to fabricate the high performance TFT through the sol-gel method. We investigated the influence of relative compositions of Ti on the electrical properties. Indium nitrate hydrate [$In(NO^3).xH_2O$] and Titanium isobutoxide [$C_{16}H_{36}O_4Ti$] were dissolved in acetylacetone. Then monoethanolamine (MEA) and acetic acid ($CH_3COOH$) were added to the solution. The molar concentration of indium was kept as 0.1 mol concentration and the amount of Ti was varied according to weighting percent (0, 5, 10%). The complex solutions become clear and homogeneous after stirring for 24 hours. Heavily boron (p+) doped Si wafer with 100nm thermally grown $SiO_2$ serve as the gate and gate dielectric of the TFT, respectively. TiInO thin films were deposited using the sol-gel solution by the spin-coating method. After coating, the films annealed in a tube furnace at $500^{\circ}C$ for 1hour under oxygen ambient. The 5% Ti-doped InO TFT had a field-effect mobility $1.15cm^2/V{\cdot}S$, a threshold voltage of 4.73 V, an on/off current ratio grater than $10^7$, and a subthreshold slop of 0.49 V/dec. The 10% Ti-doped InO TFT had a field-effect mobility $1.03\;cm^2/V{\cdot}S$, a threshold voltage of 1.87 V, an on/off current ration grater than $10^7$, and a subthreshold slop of 0.67 V/dec.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2009.05a
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• pp.111-112
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• 2009

Diamond-like carbon (DLC) is a convenient term to indicate the compositions of the various forms of amorphous carbon (a-C), tetrahedral amorphous carbon (ta-C), hydrogenated amorphous carbon and tetrahedral amorphous carbon (a-C:H and ta-C:H). The a-C film with disordered graphitic ordering, such as soot, chars, glassy carbon, and evaporated a-C, is shown in the lower left hand corner. If the fraction of sp3 bonding reaches a high degree, such an a-C is denoted as tetrahedral amorphous carbon (ta-C), in order to distinguish it from sp2 a-C [2]. Two hydrocarbon polymers, that is, polyethylene (CH2)n and polyacetylene (CH)n, define the limits of the triangle in the right hand corner beyond which interconnecting C-C networks do not form, and only strait-chain molecules are formed. The DLC films, i.e. a-C, ta-C, a-C:H and ta-C:H, have some extreme properties similar to diamond, such as hardness, elastic modulus and chemical inertness. These films are great advantages for many applications. One of the most important applications of the carbon-based films is the coating for magnetic hard disk recording. The second successful application is wear protective and antireflective films for IR windows. The third application is wear protection of bearings and sliding friction parts. The fourth is precision gages for the automotive industry. Recently, exciting ongoing study [1] tries to deposit a carbon-based protective film on engine parts (e.g. engine cylinders and pistons) taking into account not only low friction and wear, but also self lubricating properties. Reduction of the oil consumption is expected. Currently, for an additional application field, the carbon-based films are extensively studied as excellent candidates for biocompatible films on biomedical implants. The carbon-based films consist of carbon, hydrogen and nitrogen, which are biologically harmless as well as the main elements of human body. Some in vitro and limited in vivo studies on the biological effects of carbon-based films have been studied [$2{\sim}5$].The carbon-based films have great potentials in many fields. However, a few technological issues for carbon-based film are still needed to be studied to improve the applicability. Aisenberg and Chabot [3] firstly prepared an amorphous carbon film on substrates remained at room temperature using a beam of carbon ions produced using argon plasma. Spencer et al. [4] had subsequently developed this field. Many deposition techniques for DLC films have been developed to increase the fraction of sp3 bonding in the films. The a-C films have been prepared by a variety of deposition methods such as ion plating, DC or RF sputtering, RF or DC plasma enhanced chemical vapor deposition (PECVD), electron cyclotron resonance chemical vapor deposition (ECR-CVD), ion implantation, ablation, pulsed laser deposition and cathodic arc deposition, from a variety of carbon target or gaseous sources materials [5]. Sputtering is the most common deposition method for a-C film. Deposited films by these plasma methods, such as plasma enhanced chemical vapor deposition (PECVD) [6], are ranged into the interior of the triangle. Application fields of DLC films investigated from papers. Many papers purposed to apply for tribology due to the carbon-based films of low friction and wear resistance. Figure 1 shows the percentage of DLC research interest for application field. The biggest portion is tribology field. It is occupied 57%. Second, biomedical field hold 14%. Nowadays, biomedical field is took notice in many countries and significantly increased the research papers. DLC films actually applied to many industries in 2005 as shown figure 2. The most applied fields are mold and machinery industries. It took over 50%. The automobile industry is more and more increase application parts. In the near future, automobile industry is expected a big market for DLC coating. Figure 1 Research interests of carbon-based filmsFigure 2 Demand ratio of DLC coating for industry in 2005. In this presentation, I will introduce a trend of carbon-based coating research and applications.

• Korean Journal of Materials Research
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• v.18 no.12
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• pp.655-659
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• 2008

The NO gas sensing properties of ZnO-carbon nanotube (ZnO-CNT) composites fabricated by the coaxial coating of single-walled CNTs with ZnO were investigated using pulsed laser deposition. Upon examination, the morphology and crystallinity of the ZnO-CNT composites showed that CNTs were uniformly coated with polycrystalline ZnO with a grain size as small as 5-10 nm. Gas sensing measurements clearly indicated a remarkable enhancement of the sensitivity of ZnO-CNT composites for NO gas compared to that of ZnO films while maintaining the strong sensing stability of the composites, properties that CNT-based sensing materials do not have. The enhanced gas sensing properties of the ZnO-CNT composites are attributed to an increase in the surface adsorption area of the ZnO layer via the coating by CNTs of a high surface-to-volume ratio structure. These results suggest that the ZnO-CNT composite is a promising template for novel solid-state semiconducting gas sensors.

• Korean Journal of Materials Research
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• v.26 no.6
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• pp.347-352
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• 2016

ZnO with wurtzite structure has a wide band gap of 3.37 eV. Because ZnO has a direct band gap and a large exciton binding energy, it has higher optical efficiency and thermal stability than the GaN material of blue light emitting devices. To fabricate ZnO devices with optical and thermal advantages, n-type and p-type doping are needed. Many research groups have devoted themselves to fabricating stable p-type ZnO. In this study, $As^+$ ion was implanted using an ion implanter to fabricate p-type ZnO. After the ion implant, rapid thermal annealing (RTA) was conducted to activate the arsenic dopants. First, the structural and optical properties of the ZnO thin films were investigated for as-grown, as-implanted, and annealed ZnO using FE-SEM, XRD, and PL, respectively. Then, the structural, optical, and electrical properties of the ZnO thin films, depending on the As ion dose variation and the RTA temperatures, were analyzed using the same methods. In our experiment, p-type ZnO thin films with a hole concentration of $1.263{\times}10^{18}cm^{-3}$ were obtained when the dose of $5{\times}10^{14}$ As $ions/cm^2$ was implanted and the RTA was conducted at $850^{\circ}C$ for 1 min.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.08a
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• pp.339-339
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• 2012

지난 몇 년 동안, 투명 비정질 산화물 반도체는 유기 발광 다이오드, 플렉서블 전자 소자, 솔라 셀, 바이오 센서 등 많은 응용분야에 연구되고 있다. 투명 비정질 산화물 반도체 그룹들 중, 특히 비정질 IGZO 박막 트랜지스터는 비정질 상태임에도 불구하고 높은 이동도와 낮은 동작 전압으로 훌륭한 소자 특성을 보인다. 이러한 고성능의 IGZO 박막 트랜지스터는 RF 마그네트론 스퍼터링이나 pulsed laser deposition과 같은 고진공 장비를 이용하여 이미 여러 그룹에서 제작되고 발표되었다. 하지만 진공 증착 시스템은 제조 비용의 절감이나 디스플레이 패널의 대면적화에 큰 걸림돌이 되고 있고, 이러한 문제점을 극복하기 위해서 용액 공정은 하나의 해결책이 될 수 있다. 용액 공정의 가장 큰 장점으로는 저온 공정이 가능하기 때문에 글라스나 플라스틱 기판에서 대면적으로 제작할 수 있고 진공 장비가 필요없기 때문에 제조 비용을 획기적으로 절감시킬 수 있다. 본 연구에서는 high-k 게이트 절연막과 IGZO 채널 층을 용액 공정을 이용하여 박막 트랜지스터를 제작하고 그에 따른 전기적 특성을 분석하였다. IGZO의 몰 비율은 In, Ga, Zn 순으로 각각 0.2 mol, 0.1 mol, 0.1 mol로 제작하였고, high-k 게이트 절연막으로는 Al2O3, HfO2, ZrO2을 제작하였다. 또한, 용액 공정 IGZO TFT를 제작하기 전, 용액 공정 high-k 게이트 절연막 캐패시터를 제작하여 그 특성을 분석하였다. 다양한 용액 공정 high-k 게이트 절연막 중, 용액공정 HfO2를 이용한 IGZO TFT는 228.3 [mV/dec]의 subthreshold swing, 18.5 [$cm^2/V{\cdot}s$]의 유효 전계 이동도, $4.73{\times}106$의 온/오프 비율을 보여 매우 뛰어난 전기적 특성을 확인하였다.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.08a
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• pp.405-405
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• 2012

에너지 갭의 크기가 큰 ZnO는 큰 여기자 결합과 높은 화학적 안정도를 가지고 있기 때문에 전자소자 및 광소자로 많이 응용되고 있다. ZnO는 광학적 및 전기적 성질의 여러 가지 장점 때문에 메모리, 나노발전기, 트랜지스터, 태양전지, 광탐지기 및 레이저와 같은 여러 분야에 많이 사용되고 있다. Zn와 쉘 구조가 비슷한 Cu 불순물은 우수한 luminescence activator이고 다양한 불순물 레벨을 만들기 때문에 전기적 및 광학적 특성을 변화하는데 좋은 도핑 물질이다. Cu가 도핑된 ZnO 나노구조를 전기화학적 증착법을 이용하여 형성하고, 형성시간의 변화에 따른 구조적 및 광학적 성질에 대한 관찰하였다. ITO 코팅된 유리 기판에 전기화학증착법을 이용하여 Cu 도핑된 ZnO를 성장하였다. Sputtering, pulsed laser vapor deposition, 화학기상증착, atomic layer epitaxy, 전자빔증발법 등으로 Cu 도핑된 ZnO 나노구조를 형성하지만 본 연구에서는 낮은 온도와 간단한 공정으로, 속도가 빠르고 가격이 낮아 경제적인 면에서 효율적인 전기 화학증착법으로 성장하였다. 반복실험을 통하여 Cu의 도핑 농도는 Zn과 Cu의 비율이 97:3이 되도록, ITO 양극과 Pt 음극의 전위차가 -0.75V로 실험조건을 고정하였고, 성장시간을 각각 5분, 10분, 20분으로 변화하였다. 주사전자현미경 사진에서 Cu 도핑된 ZnO는 성장 시간이 증가함에 따라 나노세선 형태에서 나노로드 형태로 변하였다. X-선 회절 측정결과에서 성장시간이 변화함에 따라 피크 위치의 변화를 관찰하였다. 광루미네센스 측정 결과는 Oxygen 공핍의 증가로 보이는 500~600 nm 대의 파장에서 나타난 피크의 위치가 에너지가 큰 쪽으로 증가하였다. 위 결과로부터 성장 시간에 따른 Cu 도핑된 ZnO의 구조적 및 광학적 특성변화를 관찰하였고, 이 연구 결과는 Cu 도핑된 ZnO 나노구조 기반 전자소자 및 광소자에 응용 가능성을 보여주고 있다.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.67 no.4
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• pp.543-548
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• 2018

Ferroelectric $Bi_4Ti_3O_{12}$ films were deposited on $SrTiO_3(100)$ and Si(100) substrate by using conductive $SrRuO_3$ films as underlayer, and their ferroelectric and electrical properties were investigated depending on crystal structure and orientation. C-axis oriented $Bi_4Ti_3O_{12}$ films were grown on well lattice-matched pseudo-cubic $SrRuO_3$ films deposited on $SrTiO_3(100)$ substrate, while random-oriented polycrystalline $Bi_4Ti_3O_{12}$ films were grown on $SrRuO_3$ films deposited on Si(100) substrate. The random-oriented polycrystalline film showed a good ferroelectric hysteresis property with remanent polarization ($P_r$) of $9.4{\mu}C/cm^2$ and coercive field ($E_c$) of 84.9 kV/cm, while the c-axis oriented film showed $P_r=0.64{\mu}C/cm^2$ and $E_c=47kV/cm$ in polarizaion vs electric field curve. The c-axis oriented $Bi_4Ti_3O_{12}$ film showed a dielectric constant of about 150 and lower thickness dependence in dielectric constant compared to the random-oriented film. Furthermore, the c-axis oriented $Bi_4Ti_3O_{12}$ film showed leakage current lower than that of the polycrystalline film. The difference of ferroelectric properties in two films was explained from the viewpoint of depolarization effect due to orientation of spontaneous polarization and layered crystal structure of bismuth-base ferroelectric oxide.