• Proceedings of the Korean Vacuum Society Conference
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• 2012.08a
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• pp.360-360
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• 2012

Zn-Sn-O (Zinc-Tin-Oxide; ZTO) thin films have been gaining extensive academic and industrial attentions owing to a semiconducting channel materials applicable to large-sized flat-panel displays. Due to the constituent oxides i.e., ZnO and SnO2, the resultant Zn-Sn-O thin films possess artificially controllable bandgaps and transmittances especially effective in the visible regime. The current approach employed RF sputtering in depositing the Zn-Sn-O thin films onto glass substrates at ambient conditions. This work places its main emphases on the electrical/optical features which are closely related to the combinations of processing variables. The electrical characterizations are performed using dc-based current-voltage characteristics and ac-based impedance spectroscopy. The optical constants, i.e., refractive index and extinction coefficient, are calculated through spectroscopic ellipsometry along with the estimation of bandgaps. The charge transport of the deposited ZTO thin films is based on electrons characteristic of n-type conduction. In addition to the basic electrical/optical information, the delicate manipulation of n-type conduction is indispensible in diversifying the industrial applications of the ZTO thin films as active devices in information and energy products. Ultimately, the electrical properties are correlated to the processing variables along with the underlying mechanism which largely determines the electrical and optical properties.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.274-274
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• 2016

터치스크린패널로 응용하기 위하여 80%이상의 높은 투과도와 낮은 저항이 요구된다. 그 중에서도 무반사 효과 (anti-reflective, AR) 를 크게하여 투과도를 향상시키는 방법으로 나노구조물, 증착시 경사각, 다층박막 방법 등이 연구 개발되고 있다. 단일 박막을 이용하여 무반사 코팅을 하는 경우, 정밀한 굴절률 조절이 어려우며 낮은 반사율 영역의 선폭이 좁은 단점이 있다. 반면, 저/고굴절률 다층박막의 경우 비교적 굴절률 조절이 용이하고 가시광영역 전반적으로 높은 투과도를 가질 수 있다. plasma enhanced chemical vapor deposition (PECVD) 증착법을 이용하여 무반사 효과를 증대시키기 위해 저/고굴절률 다층구조의 박막을 두께조합에 따라 평가하였으며, 가장 널리 사용되고 있는 Sputtering증착법과 비교하여 연구하였다. 제작된 다층박막의 구조는 glass(sub.)/SiN/SiO2/ITO 이며, 무반사 코팅층인 SiN/SiO2층은 각각 PECVD와 Sputtering 증착법을 통해 성장되었고, ITO는 스퍼터링 증착법을 이용하여 동일하게 성장하였다. 그 결과 PECVD 증착법이 Sputtering 증착법에 비하여 가시광영역(400~800nm)에서 더 높은 투과도를 얻게 되었다. 결과의 차이에 대해서 PECVD 증착법과 Sputtering 증착법으로 성장된 SiN, SiO2 박막의 광학적 특성과 물리적 특성의 변화를 spectroscopic ellipsometry (SE), Rutherford backscattering (RBS), atomic force microscopy (AFM) 을 이용하여 비교, 분석하였다.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.157.1-157.1
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• 2016

In this work, we experimentally investigated the solar absorption performance of Cu-based scalable nanostructured surfaces and compared their performance with the conventional TiNOX. We fabricated Cu-based nanostructured surfaces with a controlled chemical oxidation process applicable to a large area or complex geometry. We optimized the process parameters including the chemical compounds, dipping time and process temperature. We conducted both lab-scale and outdoor experiments to characterize the conversion efficiency of each absorber surfaces with single and double glazing setup. Lab-scale experiment was conducted with $50mm{\times}50mm$ absorber sample with 1-sun condition (1kW/m2) using a solar simulator (PEC-L01) with measuring the temperature at the absorber plate, cover glass, air gap and ambient. From the lab-scale experiment, we obtained ${\sim}91^{\circ}C$ and $94^{\circ}C$ for CuO and TiNOX surfaces after 1 hr of solar illumination at single glazing, respectively. To measure the absorber performance at actual operating condition, outdoor experiment was also conducted using $110mm{\times}110mm$ absorber sample. We measured the solar flux with thermopile detector (919P-040-50). From outdoor experiment, we observed ${\sim}123^{\circ}C$ and $131^{\circ}C$ for CuO and TiNOX with 0.6 kW/m2 insolation at double glazing, respectively. We showed that the suggested nanostructured CuO solar absorber has near-equivalent collection efficiency compared with the state-of-the-art TiNOX surfaces even with much simpler manufacturing process that does not require an expensive equipment.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.371.1-371.1
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• 2016

다양한 물질계의 2차원 나노구조는 그래핀과 함께 그 고유특성으로 최근 광전소자, 전자소자, 센서, 에너지 생성 및 저장과 수소에너지 생성 등의 응용으로 매우 많은 관심을 받고 있다. 특히 층상이중수산화물 (layered-double hydroxide; LDH) 2차원 나노구조는 생성의 용이성과 층상 내 금속 이온의 교환을 통한 특성의 자유로운 제어가 가능하므로 많은 관심을 받고 있다. 층상이중수산화물 화합물은 [Zn(1-x) MIII(x)(OH)2][$An-x/n{\cdot}mH2O$] (MIII = Al, Cr, Ga; An- = CO32-, Cl-, NO3-, CH3COO-) 구조로써, Brucite-type 구조 내에서 3가 양이온의 상태에 따라서 다양한 특성을 제어할 수 있는 장점이 있다. 이러한 장점으로 인해 층상이중수산화물 화합물은 촉매나, 에너지 저장, 음이온 교환 및 흡착, 화학적 촉매, 바이오 소자 등에 응용이 연구되고 있으며, 다양한 금속 산화물을 제조하기 위한 중간자 precursor로써도 연구되고 있다. 하지만, 이러한 대부분의 연구들을 통한 결과물들이 분말 및 수용액 상태로 남게 되며, 이러한 화합물의 특성을 제어하기 어려운 문제점이 있다. 더욱이 이러한 나노구조물들을 다양한 소자로 응용하기 위해서는 상용의 실리콘이나 glass 등의 기판형태의 물질상에 성장시킬 수 있어야 하며, 그러한 기판 위에서의 형상 및 특성 제어가 용이해야 한다. 따라서 본 연구에서는 실리콘 기판을 적용한 Zn기반의 층상이중 수산화물 화합물을 성장하고, 하부물질의 조성제어를 통한 층상이중수산화물 화합물의 형상제어가 가능한 기술에 관한 연구를 보고하고자 한다. 이를 위한 하부물질의 조성은 Zn와 Al을 통해 이루어지며, 기형성된 Al2O3박막을 핵형성층으로 활용한다. 이러한 방법으로 형성된 층상이중수산화물 화합물에 대해 이차전자주사현미경, 투과전자현미경 및 X-ray회절기법을 통해 구조분석을 하고, Raman 및 광발광스펙트럼 분석을 통해 광학적 분석을 시행함으로써, 층상이중수산화물이 기판상에서 형성되는 메커니즘에 관한 규명을 시행하였다. 이러한 분석연구를 통해 핵형성층의 에칭 따라 실리콘 기판상에서 성장하는 층상이 중수산화물 화합물의 형상 및 조성이 제어되는 메커니즘을 구명하였다.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.407.1-407.1
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• 2016

Electrochromism is defined as a phenomenon which involves persistently repeated change of optical properties between bleached state and colored state by simultaneous injection of electrons and ions, sufficient to induce an electrochemical redox process. Due to this feature, considerable progress has been made in the synthesis of electrochromic (EC) materials, improvements of EC properties in EC devices such as light shutter, smart window and variable reflectance mirrors etc. Among the variable EC materials, solid-state inorganics in particular, metal oxide semiconducting materials such as nickel oxide (NiO) have been investigated extensively. The NiO that is an anodic EC material is of special interest because of high color contrast ratio, large dynamic range and low material cost. The high performance EC devices should present the use of standard industrial production techniques to produce films with high coloration efficiency, rapid switching speed and robust reversibility. Generally, the color contrast and the optical switching speed increase drastically if high surface area is used. The structure of porous thin film provides a specific surface area and can facilitate a very short response time of the reaction between the surface and ions. The large variety of methods has been used to prepare the porous NiO thin films such as sol-gel process, chemical bath deposition and sputtering. Few studies have been reported on NiO thin films made by using sol-gel method. However, compared with dry process, wet processes that have the questions of the durability and the vestige of bleached state color limit the thin films practical use, especially when prepared by sol-gel method. In this study, we synthesis the porous NiO thin films on the fluorine doped tin oxide (FTO) glass by using sputtering and anodizing method. Also we compared electrical and optical properties of NiO thin films prepared by sol gel. The porous structure is promised to be helpful to the properties enhancement of the EC devices.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.391-391
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• 2016

The carrier transport is a key factor that determines the device performances of semiconductor devices such as solar cells and transistors [1]. Particularly, devices composed of in amorphous semiconductors, the transport is often restricted by carrier trapping, associated with various defects. So far, the trapping has been studied for as-grown films at room temperature; however it has not been studied during growth under plasma processing. Here, we demonstrate the detection of trapped carriers in hydrogenated amorphous silicon (a-Si:H) films during plasma processing, and discuss the carrier trapping and defect kinetics. Using an optically pump-probe technique, we detected the trapped carriers (electrons) in an a-Si:H films during growth by a hydrogen diluted silane discharge [2]. A device-grade intrinsic a-Si:H film growing on a glass substrate was illuminated with pump and probe light. The pump induced the photocurrent, whereas the pulsed probe induced an increment in the photocurrent. The photocurrent and its increment were separately measured using a lock-in technique. Because the increment in the photocurrent originates from emission of trapped carriers, and therefore the trapped carrier density was determined from this increment under the assumption of carrier generation and recombination dynamics [2]. We found that the trapped carrier density in device grade intrinsic a-Si:H was the order of 1e17 to 1e18 cm-3. It was highly dependent on the growth conditions, particularly on the growth temperature. At 473K, the trapped carrier density was minimized. Interestingly, the detected trapped carriers were homogeneously distributed in the direction of film growth, and they were decreased once the film growth was terminated by turning off the discharge.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.217-217
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• 2016

The amorphous InGaZnO (a-IGZO) is widely accepted as a promising channel material for thin-film transistor (TFT) applications owing to their outstanding electrical properties [1, 2]. However, a-IGZO TFTs have still suffered from their bias instability with illumination [1-4]. Up to now, many researchers have studied the sub-gap density of states (DOS) as the root cause of instability. It is well known that defect states can influence on the performances and stabilities of a-IGZO TFTs. The defects states should be closely related with the deposition condition, including sputtering power, and pressure. Nevertheless, it has not been reported how these defects are created during conventional RF magnetron sputtering. In general, during conventional RF magnetron sputtering process, negative oxygen ions (NOIs) can be generated by electron attachment in oxygen atom near target surface and then accelerated up to few hundreds eV by a self-bias; at this time, the high energy bombardment of NOIs induce defects in oxide thin films. Recently, we have reported that the properties of IGZO thin films are strongly related with effects of NOIs which are generated during the sputtering process [5]. From our previous results, the electrical characteristics and the chemical bonding states of a-IGZO thin films were depended with the bombardment energy of NOIs. And also, we suggest that the deep sub-gap states in a-IGZO as well as thin film properties would be influenced by the bombardment of high energetic NOIs during the sputtering process.In this study, we will introduce our novel technology named as Magnetic Field Shielded Sputtering (MFSS) process to prevent the NOIs bombardment effects and present how much to be improved the properties of a-IGZO thin film by this new deposition method. We deposited a-IGZO thin films by MFSS on SiO2/p-Si and glass substrate at various process conditions, after which we investigated the morphology, optical and electrical properties of the a-IGZO thin films.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.319.1-319.1
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• 2016

Recently, the Al-doped ZnO (ZnO:Al) films are intensively used in thin film a-Si solar cell applications due to their high transmittance and good conductivity. The textured ZnO:Al films are used to enhance the light trapping in thin film solar cells. The wet etch process is used to texture ZnO:Al films by dipping in diluted acidic solutions like HCl or HF. During that process the glass substrate could be damaged by the acidic solution and it may be difficult to apply it for the inline mass production process since it has to be done outside the chamber. In this paper we report a new technique to control the surface morphology of RF-sputtered ZnO:Al films. The ZnO:Al films are textured with vaporized HF formed by the mixture of HF and H2SiO3 solution. Even though the surface of textured ZnO:Al films by vapor etching process showed smaller and sharper surface structures compared to that of the films textured by wet etching, the haze value was dramatically improved. We achieved the high haze value of 78% at the wavelength of 540 nm by increasing etching time and HF concentration. The haze value of about 58% was achieved at the wavelength of 800 nm when vapor texturing was used. The ZnO:Al film texture by HCl had haze ratio of about 9.5 % at 800 nm and less than 40 % at 540 nm. In addition to low haze ratio, the texturing by HCl was very difficult to control etching and to keep reproducibility due to its very fast etching speed.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.279.1-279.1
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• 2016

박막 트랜지스터 (thin film transistor, TFT)는 고밀도, 대면적화로 높은 전자의 이동도가 요구되면서, 비정질 실리콘 (a-Si)에서 다결정 실리콘 (poly-Si) TFT 로 연구되었다. 이에 따라 비정질 실리콘에서 결정질 실리콘으로의 상변화에 대한 결정화 연구가 활발히 진행되었다. 또한, 박막 태양전지 분야에서도 유리기판 위에 비정질 층을 증착한 후에 열처리를 통해 상변화하는 고상 결정화 (solid-phase crystallization, SPC) 기술을 적용하여, CSG (thin-film crystalline silicon on glass) 태양전지를 보고하였다. 이러한 비정질 실리콘 층의 결정화 기술을 결정질 실리콘 태양전지 에미터 형성 공정에 적용하고자 한다. 이 때, 플라즈마화학증착 (Plasma-enhanced chemical vapor deposition, PECVD) 장비로 증착된 비정질 실리콘 층의 열처리를 통한 결정화 정도가 중요한 요소이다. 따라서, 비정질 실리콘 층의 결정화에 영향을 주는 인자에 대해 연구하였다. 비정질 실리콘 증착 조건(H2 가스 비율, 도펀트 유무), 실리콘 기판의 결정방향, 열처리 온도에 따른 결정화 정도를 엘립소미터(elipsometer), 투과전자현미경 (transmission electron microscope, TEM), 적외선 분광기 (Fourier Transform Infrared, FT-IR) 측정을 통하여 비교 하였다. 이를 기반으로 결정화 온도에 따른 비정질 실리콘의 결정화를 위한 활성화 에너지를 계산하였다. 비정질 실리콘 증착 조건 보다 기판의 결정방향이 결정화 정도에 크게 영향을 미치는 것으로 확인하였다.

• Steel and Composite Structures
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• v.29 no.3
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• pp.405-422
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• 2018

In this research, experimental tensile test and manufacturing of carbon nanotube reinforced composite beam (CNTRC) is presented. Also, bending, buckling, and vibration analysis of CNTRC based on various beam theories such as Euler-Bernoulli, Timoshenko and Reddy beams are considered. At first, the experimental tensile tests are carried out for CNTRC and composite beams in order to obtain mechanical properties and then using Hamilton's principle the governing equations of motion are derived for Euler Bernoulli, Timoshenko and Reddy theories. The results have a good agreement with the obtained results by similar researches and it is shown that adding just two percent of carbon nanotubes increases dimensionless fundamental frequency and critical buckling load as well as decreases transverse deflection of composite beams. Also, the influences of different manufacturing processes such as hand layup and industrial methods using vacuum pump on composite properties are investigated. In these composite beams, glass fibers used in an epoxy matrix and for producing CNTRC, CNTs are applied as reinforcement particles. Applying two percent of CNTs leads to increase the mechanical properties and increases natural frequencies and critical buckling load and decreases deflection. The obtained natural frequencies and critical buckling load by theoretical method are higher than other methods, because there are some inevitable errors in industrial and hand layup method. Also, the minimum deflection occurs for theoretical methods, in bending analysis. In this study, Young's and shear modulli as well as density are obtained by experimental test and have not been used from the results of other researches. Then the theoretical analysis such as bending, buckling and vibration are considered by using the obtained mechanical properties of this research.