Inactivation of low-temperature-induced numerous defects at the electrode/channel interfaces using ultrathin Al₂O₃ layers

Jung, Sung Hyeon,Ahn, Cheol Hyoun,Kim, Young Been,Kim, Dong Su,Deshpande, Nishad G.,Cho, Hyung Koun ELSEVIER 2019 MICROELECTRONIC ENGINEERING Vol.216 No.-

<P><B>Abstract</B></P> <P>The high demand for flexible and stretchable electronics has resulted in new bottlenecks on the process design of amorphous oxide thin-film transistors (TFTs) fabricated at ≥300 °C that involves low-temperature processes to accommodate for the use of polymer substrates. Unlike previous studies aiming to achieve better channel properties, our study focuses on the low-temperature effects of electrical contacts at the source/drain electrodes and oxide channel junction. The decrease in the process temperature causes unfavorable evident changes from an almost ohmic (350 °C) to Schottky (200 °C) junction and shows coincident trends with the degradation of TFT performances. Thus, we here propose a creative process design using ultrathin Al<SUB>2</SUB>O<SUB>3</SUB> interlayers between the electrode and channel, where they inactivate the role of numerous surface defects existing on the <I>a</I>-IZO channels deposited at low temperatures. The <I>a</I>-IZO TFT with 13 Å Al<SUB>2</SUB>O<SUB>3</SUB> optimally exhibits a field effect mobility of 17.3 cm<SUP>2</SUP>/Vs in the 200 °C low-temperature annealing process, comparable to that of <I>a</I>-IZO TFT annealed at 350 °C. Similarly, the ultrathin Al<SUB>2</SUB>O<SUB>3</SUB> interlayers led to the reduced specific contact resistance and ohmic junction behavior. From capacitance–voltage analyses, we elucidated that they were attributed to the significantly reduced trapping events of the charges by passivating the interface defects.</P> <P><B>Highlights</B></P> <P> <UL> <LI> We developed an approach reducing interface contact resistance. </LI> <LI> Ohmic junction in low temperature process could be obtained with ultrathin Al<SUB>2</SUB>O<SUB>3</SUB> layer. </LI> <LI> Ultrathin Al<SUB>2</SUB>O<SUB>3</SUB> layer effectively suppressed the contribution of interface defects. </LI> <LI> This approach was effective in all low-temperature processed oxide TFTs. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Low Temperature Impact Toughness of Structural Steel Welds with Different Welding Processes

신현섭,박기태,이진형,장경호,Vuong Nguyen Van Do***** 대한토목학회 2015 KSCE JOURNAL OF CIVIL ENGINEERING Vol.19 No.5

Influence of welding process and welding consumable on the impact toughness at low temperatures of the Heat Affected Zone (HAZ) and the weld metal in a structural steel weldment was investigated. A comparison of the low temperature impact toughness was made between the welded joints fabricated by Shielded Metal Arc Welding (SMAW) and Flux Cored Arc Welding (FCAW) processes, respectively. The Charpy impact tests along with the microstructural observations and the hardness measurements were carried out to derive the effective welding method to guarantee the higher impact toughness of the HAZ and the weld metal at low temperatures. Standard V-notch Charpy impact specimens were prepared and tested under dynamic loading condition. Variation of the Charpy impact energy with respect to the test temperature and that of the hardness across the welds were presented and correlated with the microstructure and the welding process. Analysis of the results unveiled that the weld metal of the FCAW joint has a little higher low temperature impact toughness owing to the higher nickel content, whilst the HAZ of the SMAW joint has much superior impact toughness at low temperatures attributed to the lower heat input; thus the efficient welding method to ensure higher low temperature impact toughness of the HAZ and the weld metal is to employ a low heat input welding process using a welding consumable with high nickel content.

Low-temperature solution processed perovskite solar cells

이의진,김두헌,허수원,문두경 한국공업화학회 2014 한국공업화학회 연구논문 초록집 Vol.2014 No.1

Organic-inorganic hybrid perovskite solar cells that combine a mesoporous scaffold, an organometal trihalide perovskite light absorber and an organic hole transporter have exhibited high efficiencies over 12%. However, they require high processing temperatures of up to 500°C to sinter the metal-oxide paste to form the mesoporous scaffold. To fabricate low-temperature processable perovskite solar cells, we introduced sol-gel processed metal oxide scaffold. The metal oxide scaffold showed high electron mobility and enhanced surface morphology than TiO₂ scaffold. We successfully fabricated low-temperature processed perovskite solar cell devices on the sol-gel processed metal oxide scaffold. Photovoltaic performances were characterized and showed efficient power conversion efficiency.

Solution-Processable LaZrO_<i>x</i>/SiO₂ Gate Dielectric at Low Temperature of 180 °C for High-Performance Metal Oxide Field-Effect Transistors

Je, So Yeon,Son, Byeong-Geun,Kim, Hyun-Gwan,Park, Man-Young,Do, Lee-Mi,Choi, Rino,Jeong, Jae Kyeong American Chemical Society 2014 ACS APPLIED MATERIALS & INTERFACES Vol.6 No.21

<P>Although solution-processable high-k inorganic dielectrics have been implemented as a gate insulator for high-performance, low-cost transition metal oxide field-effect transistors (FETs), the high-temperature annealing (>300 °C) required to achieve acceptable insulating properties still limits the facile realization of flexible electronics. This study reports that the addition of a 2-dimetylamino-1-propanol (DMAPO) catalyst to a perhydropolysilazane (PHPS) solution enables a significant reduction of the curing temperature for the resulting SiO<SUB>2</SUB> dielectrics to as low as 180 °C. The hydrolysis and condensation of the as-spun PHPS film under humidity conditions were enhanced greatly by the presence of DMAPO, even at extremely low curing temperatures, which allowed a smooth surface (roughness of 0.31 nm) and acceptable leakage characteristics (1.8 × 10<SUP>–6</SUP> A/cm<SUP>2</SUP> at an electric field of 1MV/cm) of the resulting SiO<SUB>2</SUB> dielectric films. Although the resulting indium zinc oxide (IZO) FETs exhibited an apparent high mobility of 261.6 cm<SUP>2</SUP>/(V s), they suffered from a low on/off current (<I>I</I><SUB>ON/OFF</SUB>) ratio and large hysteresis due to the hygroscopic property of silazane-derived SiO<SUB>2</SUB> film. The <I>I</I><SUB>ON/OFF</SUB> value and hysteresis instability of IZO FETs was improved by capping the high-k LaZrO<SUB><I>x</I></SUB> dielectric on a solution-processed SiO<SUB>2</SUB> film via sol–gel processing at a low temperature of 180 °C while maintaining a high mobility of 24.8 cm<SUP>2</SUP>/(V s). This superior performance of the IZO FETs with a spin-coated LaZrO<SUB><I>x</I></SUB>/SiO<SUB>2</SUB> bilayer gate insulator can be attributed to the efficient intercalation of the 5s orbital of In<SUP>3+</SUP> ion in the IZO channel, the good interface matching of IZO/LaZrO<SUB><I>x</I></SUB> and the carrier blocking ability of PHPS-derived SiO<SUB>2</SUB> dielectric film. Therefore, the solution-processable LaZrO<SUB><I>x</I></SUB>/SiO<SUB>2</SUB> stack can be a promising candidate as a gate dielectric for low-temperature, high-performance, and low-cost flexible metal oxide FETs.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/aamick/2014/aamick.2014.6.issue-21/am504231h/production/images/medium/am-2014-04231h_0012.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/am504231h'>ACS Electronic Supporting Info</A></P>

Dieletric Engineering via Humidity Control for Solution-processed High Performance Oxide Semiconductor Thin-film Transistors

김연상 한국공업화학회 2016 한국공업화학회 연구논문 초록집 Vol.2016 No.1

Solution-processed oxide semiconductors thin film transistors (OS TFTs) with continuous, large scale, and low cost processibility have potential for next-generation display technology. Especially, studies on various precursors for high quality OS thin films in a low-temperature process have been focused for an OS film on a flexible substrate. Among them, OS TFTs fabricated with a metal aqua complex have attracted much attention because they have low temperature processibility as well as high field-effect mobility. However, despite of remarkable results, important factors to optimize their performance with a fidelity have not been achieved. Here, we demonstrate the importance of humidity control to enhance the electrical performance of OS TFTs. Through humidity control during the spin-coting process and annealing process, we successfully demonstrate solution-processed InOx/SiO₂ TFTs with a good fidelity of ~ 5% standard deviation, showing high average field-effect mobility.

Low-temperature large-area fabrication of ZnO nanowires on flexible plastic substrates by solution-processible metal-seeded hydrothermal growth

유강은,Lee Wonseok,Kang Kyungnam,김인환,Kang Daehun,Oh Dong Kyo,Kim Min Cheol,Choi Hyunsik,김광준,Kim Minwook,Kim Jeong Dae,Park Inkyu,옥종걸 나노기술연구협의회 2020 Nano Convergence Vol.7 No.24

We have developed the low-temperature conformal ZnO nanowire fabrication on flexible plastic substrates by utilizing the solution-processible metal seed-assisted hydrothermal ZnO crystallization. Structural evolution of ZnO nanowires controlled by major parameters involving growth temperature, growth time, and seed coating condition, has been systematically investigated towards uniform and large-area growth of conformal ZnO nanowires. Direct ZnO nanowire growth on flexible plastics without undergoing the high-temperature seed sintering has been realized by developing the low-temperature Ag-seeded hydrothermal ZnO nanowire growth. The nanoporous Ag layer favorable for ZnO crystal nucleation and continued nanowire growth can be reduced from the Ag ion solution coating at the temperature as low as 130 °C. This tactfully enables the selective hydrothermal growth of ZnO nanowires on the Ag patterns on flexible plastics. Such an all-solution-processible low-temperature fabrication protocol may provide an essential and practical solution to develop many diverse applications including wearable and transparent electronics, sensors, and photocatalytic devices. As one example, we demonstrate that a transparent UV sensor can be devised based on the ZNW growth on the Ag micromesh electrode.

Low-temperature solution-processed Li-doped SnO₂ as an effective electron transporting layer for high-performance flexible and wearable perovskite solar cells

Park, Minwoo,Kim, Jae-Yup,Son, Hae Jung,Lee, Chul-Ho,Jang, Seung Soon,Ko, Min Jae Elsevier 2016 Nano energy Vol.26 No.-

<P><B>Abstract</B></P> <P>Lead halide perovskite solar cells (PSCs) are thought to be promising energy power suppliers because of their feasibility for high power conversion efficiency (PCE), light weight, and flexible architecture. The preparation of charge transporting layers at low temperature has been essential for high-performance and flexible PSCs. Recently, low-temperature-processed metal oxides have been a desirable material for charge transport and air stability for PSCs, instead of organic semiconductors. However, pristine metal oxides fabricated at low temperature have still precluded high performance of the device because of their low conductivity and large deviation in energy levels from the conduction band or valance band of the perovskite. Therefore, doping metals in the metal oxides has been considered as an effective method to endow suitable electrical properties. Herein, we developed a highly efficient electron transporting layer (ETL) comprising Li-doped SnO<SUB>2</SUB> (Li:SnO<SUB>2</SUB>) prepared at low temperature in solution. The doped Li in SnO<SUB>2</SUB> enhanced conductivity as well as induced a downward shift of the conduction band minimum of SnO<SUB>2</SUB>, which facilitated injection and transfer of electrons from the conduction band of the perovskite. The PCE was measured to be 18.2% and 14.78% for the rigid and flexible substrates, respectively. The high-performance and flexible PSCs could be potentially used as a wearable energy power source.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Li:SnO<SUB>2</SUB> and SnO<SUB>2</SUB> are used as an electron transporting layer in perovskite solar cells. </LI> <LI> The performance of the devices is enhanced after Li-doping in SnO<SUB>2</SUB>. </LI> <LI> Low-temperature and solution process realize high-performance wearable perovskite solar cells. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Low temperature solution processable TiO₂ nano-sol for electron transporting layer of flexible perovskite solar cells

You, Myung Sang,Heo, Jin Hyuck,Park, Jin Kyoung,Moon, Sang Hwa,Park, Bum Jun,Im, Sang Hyuk Elsevier 2019 Solar energy materials and solar cells Vol.194 No.-

<P><B>Abstract</B></P> <P>Low-temperature solution processable TiO<SUB>2</SUB> nano-sol for electron transporting layer (ETL) of flexible perovskite solar cells is prepared by synthesizing TiO<SUB>2</SUB> nano-sols by peptization in acidic aqueous solution and re-dispersing the TiO<SUB>2</SUB> nanoparticles in H<SUB>2</SUB>O, ethanol (EtOH), dimethylsulfoxied (DMSO), and N,N-dimethylformamide (DMF). By considering dielectric constant, zeta potential, and surface tension of solvent media, we found that the DMF is the best to form uniform TiO<SUB>2</SUB> ETL by spin-coating among them because it has low surface tension and high zeta potential. Accordingly, we could demonstrate 18.2% power conversion efficiency (PCE) for rigid glass substrate based perovskite solar cells and 15.8% PCE for flexible polymer substrate based devices by low-temperature solution process.</P> <P><B>Highlights</B></P> <P> <UL> <LI> TiO<SUB>2</SUB> nano-sol is prepared by sol-gel reaction at acidic aqueous phase. </LI> <LI> TiO<SUB>2</SUB> electron transporting layer is formed by low temperature solution process. </LI> <LI> Low temperature processed perovskite rigid and flexible solar cells exhibit 18.2% and 15.8% efficiency. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

폐타이어 고무분말 개질 아스팔트의 물리적 특성에 대한 공정조건의 영향

오광중,김종석 한국도로학회 2008 한국도로학회논문집 Vol.10 No.3

본 연구는 폐타이어 고무분말 개질 아스팔트 (crumb rubber modified asphalt, CRMA) 공정조건에서반응온도, 혼합반응시간 및 유연성 개질제의 영향을 조사하였다. 저온에서 아스팔트바인더와 개질 아스팔트의 온도 민감성과 접착특성은 침입도와 인장접착강도를 통하여 측정하였다. 유연제와 공정온도가 인장접착강도와 강인화 에너지의 중요 한 요소임을 확인하였다. 더 높은 혼합온도와 연성 개질제에서 CRMA의 인장접착물성이 향상되는 것은 아스팔트바인 더와 개질 아스팔트의 연성구조에 기인한다. CRMA의 물리적 특성의 개선은 CR과 아스팔트바인더간의 상용성에 있다. 유연제가 CR과 아스팔트바인더 안에 침투되어, 유연제에 의해 개질된 CRMA는 CRMA보다 접착특성이 증가하였 음을 확인하였다 asphalts at low temperature measured using the penetration and tensile adhesion test. It was found that processing temperatures and flexible modifier were important factors for tensile adhesion strength and toughness energy at low temperature. The CRMA in the higher processing temperature and flexible modifier exhibited improved tensile adhesion properties which indicated the flexible structure of neat and modified asphalt binder. In general, the improvements of the physical properties in the CRMAs were due to the improvements of miscibility between CR and asphalt binder. It was found that the adhesion properties of the flexible agent modified CRMA were higher than CRMA were related to the flexible agent tend to penetrate into CR particles and asphalt binder. In this study, the influence of reaction temperatures, mixing time and flexible modifier for crumb rubber modified asphalt (CRMA) as processing conditions were investigated. The temperature susceptibility and adhesion properties of neat and modified asphalts at low temperature measured using the penetration and tensile adhesion test. It was found that processing temperatures and flexible modifier were important factors for tensile adhesion strength and toughness energy at low temperature. The CRMA in the higher processing temperature and flexible modifier exhibited improved tensile adhesion properties which indicated the flexible structure of neat and modified asphalt binder. In general, the improvements of the physical properties in the CRMAs were due to the improvements of miscibility between CR and asphalt binder. It was found that the adhesion properties of the flexible agent modified CRMA were higher than CRMA were related to the flexible agent tend to penetrate into CR particles and asphalt binder.

저온프로세스를 이용한 고분자필름의 플라즈마 표면처리

조욱,양성채,Cho, Wook,Yang, Sung-Chae 한국전기전자재료학회 2008 전기전자재료학회논문지 Vol.21 No.5

The plasma processing is applied to many industrial fields as thin film deposition or surface treatment technique. In this study, we investigated large-area uniformed surface treatment of PET film at low temperature by using Scanning Plasma Method(SPM). Then, we measured difference and distribution of temperature on film's surface by setting up a thermometer. We studied the condition of plasma for surface treatment by examining intensity of irradiation of uniformed plasma. And we compared contact angles of treated PET film by using Ar and $O_2$ plasma based low temperature. In our result, surface temperature of 3-point of treating is low temperature about $22^{\circ}C$, in other hands, there is scarcely any variation of temperature on film's surface. And by using Ar plasma treatment, contact angle is lower than untreatment or $O_2$ plasma treatment. In case of PET film having thermal weak point, low temperature processing using SPM is undamaged method in film's surface and uniformly treated film's surface. As a result, Ar plasma surface treatment using SPM is suitable surface treatment method of PET film.