Publications by authors named "Woojin Jeon"

24 Publications

  • Page 1 of 1

Discovery of μ,δ-Opioid Receptor Dual-Biased Agonists That Overcome the Limitation of Prior Biased Agonists.

ACS Pharmacol Transl Sci 2021 Jun 6;4(3):1149-1160. Epub 2021 Apr 6.

Research Laboratory, Ildong Pharmaceutical Co., Ltd., 20, Samsung 1-ro 1-gil, Hwaseong 18449, Korea.

Morphine is widely used in pain management although the risk of side effects is significant. The use of biased agonists to the G protein of μ-opioid receptors has been suggested as a potential solution, although oliceridine and PZM21 have previously failed to demonstrate benefits in clinical studies. An amplification-induced confusion in the process of comparing G protein and beta-arrestin pathways may account for previously biased agonist misidentification. Here, we have devised a strategy to discover biased agonists with intrinsic efficacy. We computationally simulated 430 000 molecular dockings to the μ-opioid receptor to construct a compound library. Hits were then verified experimentally. Using the verified compounds, we performed simulations to build a second library with a common scaffold and selected compounds that showed a bias to μ- and δ-opioid receptors in a cell-based assay. Three compounds (ID110460001, ID110460002, and ID110460003) with a dual-biased agonistic effect for μ- and δ-opioid receptors were identified. These candidates are full agonists for the μ-opioid receptor and show specific binding modes. On the basis of our findings, we expect our novel compounds to act as more biased agonists compared to existing drugs, including oliceridine.
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http://dx.doi.org/10.1021/acsptsci.1c00044DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8204323PMC
June 2021

Improved Properties of the Atomic Layer Deposited Ru Electrode for Dynamic Random-Access Memory Capacitor Using Discrete Feeding Method.

ACS Appl Mater Interfaces 2021 May 16;13(20):23915-23927. Epub 2021 May 16.

Department of Materials Science and Engineering and Inter-University Semiconductor Research Center, Seoul National University, Seoul 08826, Republic of Korea.

Ruthenium (Ru) thin films deposited via atomic layer deposition (ALD) with a normal sequence and discrete feeding method (DFM) and their performance as a bottom electrode of dynamic random-access memory (DRAM) capacitors were compared. The DFM-ALD was performed by dividing the Ru feeding and purge steps of the conventional ALD process into four steps (shorter feeding time + purge time). The surface morphology of the Ru films was improved significantly with the DFM-ALD, and the preferred orientation of the Ru films was changed from relatively random to a <101>-oriented direction. Under the DFM-ALD condition, the higher susceptibility of oxygen atoms to the Ru electrode resulted in a higher proportion of the RuO formation on the Ru film surface during the subsequent TiO ALD process. This higher RuO portion leads to higher crystallinity of the local-epitaxially grown TiO films with a rutile phase. Such improvement also decreased the interfacial component of equivalent oxide thickness (EOT) by ∼0.1 nm compared with the cases on sputtered Ru film, which showed an even smoother surface morphology. Consequently, the minimum EOT values when the Ru bottom electrodes deposited via DFM-ALD were adopted were 0.76 and 0.48 nm for TiO and Al-doped TiO films, respectively, while still satisfying the DRAM leakage current density specification (<10 A/cm at a capacitor voltage of 0.8 V).
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http://dx.doi.org/10.1021/acsami.1c03795DOI Listing
May 2021

Computational and Histological Analyses for Investigating Mechanical Interaction of Thermally Drawn Fiber Implants with Brain Tissue.

Micromachines (Basel) 2021 Apr 2;12(4). Epub 2021 Apr 2.

Department of Bio and Brain Engineering, Korea Advanced Institute of Science and Technology (KAIST), Deajeon 34141, Korea.

The development of a compliant neural probe is necessary to achieve chronic implantation with minimal signal loss. Although fiber-based neural probes fabricated by the thermal drawing process have been proposed as a solution, their long-term effect on the brain has not been thoroughly investigated. Here, we examined the mechanical interaction of thermally drawn fiber implants with neural tissue through computational and histological analyses. Specifically, finite element analysis and immunohistochemistry were conducted to evaluate the biocompatibility of various fiber implants made with different base materials (steel, silica, polycarbonate, and hydrogel). Moreover, the effects of the coefficient of friction and geometric factors including aspect ratio and the shape of the cross-section on the strain were investigated with the finite element model. As a result, we observed that the fiber implants fabricated with extremely softer material such as hydrogel exhibited significantly lower strain distribution and elicited a reduced immune response. In addition, the implants with higher coefficient of friction (COF) and/or circular cross-sections showed a lower strain distribution and smaller critical volume. This work suggests the materials and design factors that need to be carefully considered to develop future fiber-based neural probes to minimize mechanical invasiveness.
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http://dx.doi.org/10.3390/mi12040394DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8067235PMC
April 2021

Sustainable resistance switching performance from composite-type ReRAM device based on carbon [email protected] core-shell wires.

Sci Rep 2020 11 2;10(1):18830. Epub 2020 Nov 2.

Department of Advanced Materials Engineering for Information and Electronics, Kyung Hee University, Yongin, 17104, Korea.

A novel nanocomposite-based non-volatile resistance switching random access memory device introducing single-walled carbon nanotube (SWCNT)@TiO core-shell wires was proposed for flexible electronics. The SWCNT was de-bundled by ultrasonication with sodium dodecylbenzene sulfonate (SDBS), and then the TiO skin layer on the SWCNT surface was successfully introduced by adding benzyl alcohol as a weak surfactant. The nanocomposite resistance switching layer was composed of the [email protected] core-shell wires and poly(vinyl alcohol) (PVA) matrix by a simple spin-coating method. The device exhibited reproducible resistance switching performance with a remarkably narrow distribution of operating parameters (V and V were 2.63 ± 0.16 and 0.95 ± 0.11 V, respectively) with a large R/R ratio of 10 for 200 consecutive switching cycles. Furthermore, the excellent resistance switching behavior in our device was maintained against mechanical stress up to 10 bending test. We believe that the nanocomposite memory device with [email protected] core-shell wires would be a critical asset to realize practical application for a flexible non-volatile memory field.
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http://dx.doi.org/10.1038/s41598-020-75944-3DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7608622PMC
November 2020

Modulation of the adsorption chemistry of a precursor in atomic layer deposition to enhance the growth per cycle of a TiO thin film.

Phys Chem Chem Phys 2021 Feb;23(4):2568-2574

Department of Advanced Materials Engineering for Information and Electronics, Kyung Hee University, Gyeonggi 17104, Korea.

Atomic layer deposition (ALD) has scarcely been utilized in large-scale manufacturing and industrial processes due to its low productivity, even though it possesses several advantages for improving the device performance. The major cause of its low productivity is the slow growth rate, which is determined by the amount of chemisorbed precursor. The slow growth rate of ALD has become even more critical due to the introduction of heteroleptic-based precursors for achieving a higher thermal stability. In this study, we investigated the theoretical and experimental chemisorption characteristics of the Ti(CpMe5)(OMe)3 precursor during the ALD of TiO2. By density functional theory calculations, the relationship between the steric hindrance effect and the chemistry of a chemisorbed precursor was revealed. Based on the calculation result, a way for improving the growth per cycle by 50% was proposed and demonstrated, successfully.
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http://dx.doi.org/10.1039/d0cp04176aDOI Listing
February 2021

Chemistry of ruthenium as an electrode for metal-insulator-metal capacitor application.

Nanotechnology 2021 Jan;32(4):045201

Department of Advanced Materials Engineering for Information and Electronics, Kyung Hee University, Yongin, Gyeonggi 17104, Republic of Korea.

Notwithstanding its excellent properties such as high work function and low resistance, Ru has not been widely applied in the preparation of electrodes for various electronic devices. This is because of the occurrence of severe morphological degradation in the actual devices employing Ru. Herein, we investigated Ru chemistry for electrode application and the degradation mechanism of Ru during subsequent processes such as thin film deposition or thermal annealing. We revealed that subsurface oxygen induces Ru degradation owing to the alteration of Ru chemistry by the pretreatment under various gas ambient conditions and due to the growth behavior of TiO deposited via atomic layer deposition (ALD). The degradation of Ru is successfully ameliorated by conducting an appropriate pretreatment prior to ALD. The TiO thin film deposited on the pretreated Ru electrode exhibited a rutile-phased crystal structure and smooth surface morphology, thereby resulting in excellent electrical properties. This paper presents an important development in the application of Ru as the electrode that can facilitate the development of various next-generation electronic devices.
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http://dx.doi.org/10.1088/1361-6528/abbf6aDOI Listing
January 2021

Defect Analysis and Reliability Characteristics of (HfZrO₄)(SiO₂) High- Dielectrics.

J Nanosci Nanotechnol 2020 11;20(11):6718-6722

Department of Electrical and Computer Engineering, Sungkyunkwan University, Suwon 16419, Republic of Korea.

Hafnium zirconium silicon oxide ((HfZrO₄)1-(SiO₂)) materials were investigated through the defect analysis and reliability characterization for next generation high- dielectric. Silicate doped hafnium zirconium oxide (HfZrO) films showed a reduction of negative flat-band voltage () shift compared to pure HfZrO₄. This result was caused by a decrease in donor-like interface traps (Dit) and positive border traps (). As the silicon oxide (SiO₂) content increased, the was shifted in the positive direction from -1.23 to -1.10 to -0.91 V and the slope of the capacitance-voltage (C-V) curve increased. The nonparallel shift of the C-V characteristics was affected by the , while the was responsible for the parallel C-V curve shift. The values of reduced from 4.3 × 10, 3.5 × 10, and 3.0 × 10 cmeV, as well as the values of were decreased from 5.24, 3.90 to 2.26 × 10 cm. Finally, reduction of defects in the HfZrO₄-base film with an addition of SiO₂ affected the gate oxide reliability characteristics, such as gate leakage current (), bias temperature stress instability (BTSI), and time dependent gate dielectric breakdown (TDDB).
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http://dx.doi.org/10.1166/jnn.2020.18791DOI Listing
November 2020

Hafnium Incorporation in InZnO Thin Film Transistors as a Carrier Suppressor.

J Nanosci Nanotechnol 2020 Nov;20(11):6675-6678

Department of Electrical and Computer Engineering, Sungkyunkwan University, Suwon 16419, Republic of Korea.

In this study, we fabricated Hf-doped indium zinc oxide thin-film transistors (HIZO TFTs) using a solution process. Channel layers of the TFTs were optimized by varying the molar ratio of Hf in the channel layers. The electrical properties of the fabricated devices were compared to gallium indium zinc oxide (GIZO). HIZO TFTs showed 0.12 V threshold voltage, 0.45 V/decade subthreshold swing and 1.24 × 10 on-off current ratio, which were excellent compared to that of GIZO. In particular, when a positive gate bias stress of 10 V was applied for 10³ s, the HIZO TFT exhibited a lower threshold voltage shift of 1.11 V than the GIZO TFT (1.88 V). These results originate from the higher oxygen bonding with Hf in IZO compared to Ga atoms. We confirmed that Hf acts as an excellent carrier suppressor whose properties exceed those of Ga.
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http://dx.doi.org/10.1166/jnn.2020.18761DOI Listing
November 2020

Solution-Based Indium-Zinc Oxide/Indium-Gallium-Zinc Oxide Double-Channel Thin-Film Transistors with Incorporated Hydrogen Peroxide.

J Nanosci Nanotechnol 2020 Nov;20(11):6643-6647

Department of Electrical and Computer Engineering, Sungkyunkwan University, Suwon 16419, Republic of Korea.

We fabricated and evaluated solution-based double-channel thin-film transistors (TFTs) that consisted of an indium-zinc oxide (IZO) front layer and an indium-gallium-zinc oxide (IGZO) back channel with the addition of hydrogen peroxide (H₂O₂). The devices showed superior electrical properties with regard to saturation mobility (12.9 cm₂/V·s), the on-off ratio (5 × 10), and the subthreshold swing (0.21 V/decade). All the devices were subjected under bias and illumination stress for reliability assessment. The threshold voltage shift stability of positive and negative bias illumination stress under different wavelengths was also enhanced. Thus, we achieved improved performance using IZO/IGZO TFTs with back channels that incorporated H₂O₂.
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http://dx.doi.org/10.1166/jnn.2020.18760DOI Listing
November 2020

Multimaterial and multifunctional neural interfaces: from surface-type and implantable electrodes to fiber-based devices.

J Mater Chem B 2020 08;8(31):6624-6666

Department of Bio and Brain Engineering, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 34141, Republic of Korea.

Neural interfaces have enabled significant advancements in neuroscience and paved the way for clinical applications in the diagnosis, treatment, and prevention of neurological disorders. A variety of device modalities, such as electrical, chemical and optical neural interfacing, are required for the comprehensive monitoring and modulation of neural activity. The development of recent devices with multimodal functionalities has been driven by innovations in materials engineering, especially the utilization of organic soft materials such as polymers, carbon allotropes, and hydrogels. A transition from rigid to soft materials has improved device performance through enhanced biocompatibility and flexibility to realize stable long-term performance. This article provides a comprehensive review of a variety of neural probes ranging from surface-type and implantable electrodes to fiber-based devices. We also highlight the influence of materials on the development of these neural interfaces and their effects on device performance and lifetime.
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http://dx.doi.org/10.1039/d0tb00872aDOI Listing
August 2020

The Effects of Curcuma longa L., Purple Sweet Potato, and Mixtures of the Two on Immunomodulation in C57BL/6J Mice Infected with LP-BM5 Murine Leukemia Retrovirus.

J Med Food 2018 Jul 4;21(7):689-700. Epub 2018 Jun 4.

1 Department of Medical Nutrition, Kyung Hee University , Yongin, Korea.

The immune response is stimulated to protect the body from external antigens and is controlled by several types of immune cells. In the present study, the immunomodulatory effects of Curcuma longa L., purple sweet potato, and mixtures of the two (CPM) were investigated in C57BL/6 mice infected with LP-BM5 murine leukemia virus (MuLV). Mice were divided into seven groups as follows: normal control, infected control (LP-BM5 MuLV infection), positive control (LP-BM5 MuLV infection+dietary supplement of red ginseng 300 mg/kg body weight), the original powder of C. longa L. (C; LP-BM5 MuLV infection+dietary supplement of C 189 mg/kg body weight), the original powder of purple sweet potato (P; LP-BM5 MuLV infection+dietary supplement of P 1811 mg/kg body weight), CPM Low (CPL; LP-BM5 MuLV infection+CPM 2 g/kg body weight), and CPM High (CPH; LP-BM5 MuLV infection+CPM 5 g/kg body weight). Dietary supplementation lasted for 12 weeks. Dietary supplementation of CPM inhibited LP-BM5 MuLV-induced lymphadenopathy and splenomegaly and inhibited reduction of messenger RNA (mRNA) expression of major histocompatibility complex (MHC) I and II. Moreover, CPM reduced the decrease in T- and B cell proliferation, reduced the population of CD4(+)/CD8(+) T cells, and remedied the unbalanced production of T helper-1 (Th1)/T helper-2 (Th2) cytokines in LP-BM5 MuLV-infected mice. In addition, CPM inhibited reduction of phagocytosis in peritoneal macrophages and decreased serum levels of immunoglobulin A (IgA), immunoglobulin E (IgE), and immunoglobulin G (IgG). These results suggest that CPM had a positive effect on immunomodulation in C57BL/6 mice induced by LP-BM5 leukemia retrovirus infection.
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http://dx.doi.org/10.1089/jmf.2017.4093DOI Listing
July 2018

Quantitative Analysis of the Incorporation Behaviors of Sr and Ti Atoms During the Atomic Layer Deposition of SrTiO Thin Films.

ACS Appl Mater Interfaces 2018 Mar 5;10(10):8836-8844. Epub 2018 Mar 5.

Department of Materials Science and Engineering and Inter-University Semiconductor Research Center , Seoul National University , Seoul 08826 , Republic of Korea.

The atomic layer deposition (ALD) of multication oxide films is complicated because the deposition behaviors of the component oxides are not independent of one another. In this study, the Ti and Sr atom incorporation behaviors during the ALD of SrTiO films were quantitatively examined via the carefully designed ALD process sequences. HO and O were adopted as the oxygen sources of the SrO subcycles, whereas only O was used for the TiO ALD subcycles. Apart from the general conjecture on the roles of the different types of oxygen sources, the oxygen source that was adopted for the subcycles of the other component oxide had almost complete control of the metal atom incorporation behaviors. This means that the first half-cycle of ALD played a dominant role in determining the metal incorporation rate, which revealed the critical role of the steric hindrance effect during the metal precursor injection for the ALD rate. O had almost doubled its reactivity toward the Ti and Sr precursors compared with HO. Although these are the expected results from the common knowledge on ALD, the quantitative analysis of the incorporation behaviors of each metal atom provided insightful viewpoints for the ALD process of this technically important oxide material. Furthermore, the SrTiO films with a bulk dielectric constant as high as 236 were obtained by the Ru-SrTiO-RuO capacitor structure.
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http://dx.doi.org/10.1021/acsami.7b18807DOI Listing
March 2018

Wafer-Scale Synthesis of Reliable High-Mobility Molybdenum Disulfide Thin Films via Inhibitor-Utilizing Atomic Layer Deposition.

Adv Mater 2017 Dec 2;29(47). Epub 2017 Nov 2.

Device Laboratory, Device and System Research Center, Samsung Advanced Institute of Technology, Suwon, 16678, Republic of Korea.

A reliable and rapid manufacturing process of molybdenum disulfide (MoS ) with atomic-scale thicknesses remains a fundamental challenge toward its successful incorporation into high-performance nanoelectronics. It is imperative to achieve rapid and scalable production of MoS exhibiting high carrier mobility and excellent on/off current ratios simultaneously. Herein, inhibitor-utilizing atomic layer deposition (iALD) is presented as a novel method to meet these requirements at the wafer scale. The kinetics of the chemisorption of Mo precursors in iALD is governed by the reaction energy and the steric hindrance of inhibitor molecules. By optimizing the inhibition of Mo precursor absorption, the nucleation on the substrate in the initial stage can be spontaneously tailored to produce iALD-MoS thin films with a significantly increased grain size and surface coverage (>620%). Moreover, highly crystalline iALD-MoS thin films, with thicknesses of only a few layers, excellent room temperature mobility (13.9 cm V s ), and on/off ratios (>10 ), employed as the channel material in field effect transistors on 6″ wafers, are successfully prepared.
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http://dx.doi.org/10.1002/adma.201703031DOI Listing
December 2017

Mesostructured HfxAlyO2 Thin Films as Reliable and Robust Gate Dielectrics with Tunable Dielectric Constants for High-Performance Graphene-Based Transistors.

ACS Nano 2016 07 1;10(7):6659-66. Epub 2016 Jul 1.

Device Lab., Device & System Research Center, Samsung Advanced Institute of Technology , Suwon 16678, Republic of Korea.

We introduce a reliable and robust gate dielectric material with tunable dielectric constants based on a mesostructured HfxAlyO2 film. The ultrathin mesostructured HfxAlyO2 film is deposited on graphene via a physisorbed-precursor-assisted atomic layer deposition process and consists of an intermediate state with small crystallized parts in an amorphous matrix. Crystal phase engineering using Al dopant is employed to achieve HfO2 phase transitions, which produce the crystallized part of the mesostructured HfxAlyO2 film. The effects of various Al doping concentrations are examined, and an enhanced dielectric constant of ∼25 is obtained. Further, the leakage current is suppressed (∼10(-8) A/cm(2)) and the dielectric breakdown properties are enhanced (breakdown field: ∼7 MV/cm) by the partially remaining amorphous matrix. We believe that this contribution is theoretically and practically relevant because excellent gate dielectric performance is obtained. In addition, an array of top-gated metal-insulator-graphene field-effect transistors is fabricated on a 6 in. wafer, yielding a capacitance equivalent oxide thickness of less than 1 nm (0.78 nm). This low capacitance equivalent oxide thickness has important implications for the incorporation of graphene into high-performance silicon-based nanoelectronics.
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http://dx.doi.org/10.1021/acsnano.6b01734DOI Listing
July 2016

Frustration of Negative Capacitance in Al2O3/BaTiO3 Bilayer Structure.

Sci Rep 2016 Jan 8;6:19039. Epub 2016 Jan 8.

Department of Materials Science &Engineering and Inter-university Semiconductor Research Center, College of Engineering, Seoul National University, Seoul 151-744, Republic of Korea.

Enhancement of capacitance by negative capacitance (NC) effect in a dielectric/ferroelectric (DE/FE) stacked film is gaining a greater interest. While the previous theory on NC effect was based on the Landau-Ginzburg-Devonshire theory, this work adopted a modified formalism to incorporate the depolarization effect to describe the energy of the general DE/FE system. The model predicted that the SrTiO3/BaTiO3 system will show a capacitance boost effect. It was also predicted that the 5 nm-thick Al2O3/150 nm-thick BaTiO3 system shows the capacitance boost effect with no FE-like hysteresis behavior, which was inconsistent with the experimental results; the amorphous-Al2O3/epitaxial-BaTiO3 system showed a typical FE-like hysteresis loop in the polarization - voltage test. This was due to the involvement of the trapped charges at the DE/FE interface, originating from the very high field across the thin Al2O3 layer when the BaTiO3 layer played a role as the NC layer. Therefore, the NC effect in the Al2O3/BaTiO3 system was frustrated by the involvement of reversible interface charge; the highly stored charge by the NC effect of the BaTiO3 during the charging period could not be retrieved during the discharging process because integral part of the polarization charge was retained within the system as a remanent polarization.
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http://dx.doi.org/10.1038/srep19039DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4705700PMC
January 2016

Analysis of Job Stress, Psychosocial Stress and Fatigue among Korean Police Officers.

Iran J Public Health 2014 May;43(5):687-8

2. Dept. of International Radiological Science, Hallym University of Graduate Studies, Seoul, Republic of Korea.

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http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4449418PMC
May 2014

High-concentration boron doping of graphene nanoplatelets by simple thermal annealing and their supercapacitive properties.

Sci Rep 2015 May 5;5:9817. Epub 2015 May 5.

1] Photo-electronic Hybrids Research Center, Korea Institute of Science and Technology (KIST), Seoul 136-791, Korea [2] Nano-Materials and Engineering, Korea University of Science and Technology (UST), Dae-Jeon, Korea.

For the utilization of graphene in various energy storage and conversion applications, it must be synthesized in bulk with reliable and controllable electrical properties. Although nitrogen-doped graphene shows a high doping efficiency, its electrical properties can be easily affected by oxygen and water impurities from the environment. We here report that boron-doped graphene nanoplatelets with desirable electrical properties can be prepared by the simultaneous reduction and boron-doping of graphene oxide (GO) at a high annealing temperature. B-doped graphene nanoplatelets prepared at 1000 °C show a maximum boron concentration of 6.04 ± 1.44 at %, which is the highest value among B-doped graphenes prepared using various methods. With well-mixed GO and g-B2O3 as the dopant, highly uniform doping is achieved for potentially gram-scale production. In addition, as a proof-of-concept, highly B-doped graphene nanoplatelets were used as an electrode of an electrochemical double-layer capacitor (EDLC) and showed an excellent specific capacitance value of 448 F/g in an aqueous electrolyte without additional conductive additives. We believe that B-doped graphene nanoplatelets can also be used in other applications such as electrocatalyst and nano-electronics because of their reliable and controllable electrical properties regardless of the outer environment.
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http://dx.doi.org/10.1038/srep09817DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4419459PMC
May 2015

Structure and electrical properties of Al-doped HfO₂ and ZrO₂ films grown via atomic layer deposition on Mo electrodes.

ACS Appl Mater Interfaces 2014 Dec 4;6(24):22474-82. Epub 2014 Dec 4.

Department of Materials Science and Engineering and Inter-University Semiconductor Research Center, Seoul National University , Seoul 151-742, Republic of Korea.

The effects of Al doping in atomic-layer-deposited HfO2 (AHO) and ZrO2 (AZO) films on the evolutions of their crystallographic phases, grain sizes, and electric properties, such as their dielectric constants and leakage current densities, were examined for their applications in high-voltage devices. The film thickness and Al-doping concentration were varied in the ranges of 60-75 nm and 0.5-9.7%, respectively, for AHO and 55-90 nm and 1.0-10.3%, respectively, for AZO. The top and bottom electrodes were sputtered Mo films. The detailed structural and electrical property variations were examined as functions of the Al concentration and film thickness. The AHO films showed a transition from the monoclinic phase (Al concentration up to 1.4%) to the tetragonal/cubic phase (Al concentration 2.0-3.5%), and finally, to the amorphous phase (Al concentration >4.7%), whereas the AZO films remained in the tetragonal/cubic phase up to the Al concentration of 6.4%. For both the AHO and AZO films, the monoclinic and amorphous phases had dielectric constants of 20-25, and the tetragonal/cubic phases had dielectric constants of 30-35. The highest electrical performance levels for the application to the high-voltage charge storage capacitors in flat panel displays were achieved with the 4.7-9.7% Al-doped AHO films and the 2.6% Al-doped AZO films.
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http://dx.doi.org/10.1021/am506525sDOI Listing
December 2014

Evaluating the top electrode material for achieving an equivalent oxide thickness smaller than 0.4 nm from an Al-doped TiO₂ film.

ACS Appl Mater Interfaces 2014 Dec 25;6(23):21632-7. Epub 2014 Nov 25.

Department of Materials Science and Engineering and Inter-university Semiconductor Research Center, Seoul National University , 1 Gwanak-ro, Gwanak-gu, Seoul 151-742, Republic of Korea.

The effects of Pt and RuO2 top electrodes on the electrical properties of capacitors with Al-doped TiO2 (ATO) films grown on the RuO2 bottom electrode by an atomic layer deposition method were examined. The rutile phase ATO films with high bulk dielectric constant (>80) were well-grown because of the local epitaxial relationship with the rutile structured RuO2 bottom electrode. However, the interface between top electrode and ATO was damaged during the sputtering process of the top electrode, resulting in the decrease in the dielectric constant. Postmetallization annealing at 400 °C was performed to mitigate the sputtering damage. During the postmetallization annealing, the ATO layer near the RuO2 top electrode/ATO interface was well-crystallized because of the structural compatibility between RuO2 and rutile ATO, while the ATO layer near the Pt top electrode/ATO interface still exhibited an amorphous-like structure. Despite the same thickness of the ATO films, therefore, the capacitors with RuO2 top electrodes showed higher capacitance compared to the capacitors with Pt top electrodes. Eventually, an extremely low equivalent oxide thickness of 0.37 nm with low enough leakage current density (<1 × 10(-7) A/cm(2) at 0.8 V) and physical thickness of 8.7 nm for the next-generation dynamic random access memory was achieved from ATO films with RuO2 top electrodes.
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http://dx.doi.org/10.1021/am506677eDOI Listing
December 2014

Controlling the Al-doping profile and accompanying electrical properties of rutile-phased TiO2 thin films.

ACS Appl Mater Interfaces 2014 May 1;6(10):7910-7. Epub 2014 May 1.

Department of Materials Science and Engineering and Inter-university Semiconductor Research Center, Seoul National University , Seoul 151-742, Republic of Korea.

The role of Al dopant in rutile-phased TiO2 films in the evaluation of the mechanism of leakage current reduction in Al-doped TiO2 (ATO) was studied in detail. The leakage current of the ATO film was strongly affected by the Al concentration at the interface between the ATO film and the RuO2 electrode. The conduction band offset of the interface increased with the increase in the Al dopant concentration in the rutile TiO2, which reduced the leakage current in the voltage region pertinent to the next-generation dynamic random access memory application. However, the Al doping in the anatase TiO2 did not notably increase the conduction band offset even with a higher Al concentration. The detailed analyses of the leakage conduction mechanism based on the quantum mechanical transfer-matrix method showed that Schottky emission and Fowler-Nordheim tunneling was the dominant leakage conduction mechanism in the lower and higher voltage regions, respectively. The chemical analyses using X-ray photoelectron spectroscopy corroborated the electrical test results.
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http://dx.doi.org/10.1021/am501247uDOI Listing
May 2014

Highly improved uniformity in the resistive switching parameters of TiO2 thin films by inserting Ru nanodots.

Adv Mater 2013 Apr 6;25(14):1987-92. Epub 2013 Feb 6.

WCU Hybrid Materials Program, Department of Materials Science and Engineering and Inter-university Semiconductor Research Center, Seoul National University, Seoul, Korea.

Limiting the location where electron injection occurs at the cathode interface to a narrower region is the key factor for achieving a highly improved RS performance, which can be achieved by including Ru Nanodots. The development of a memory cell structure truly at the nanoscale with such a limiting factor for the electric-field distribution can solve the non-uniformity issue of future ReRAM.
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http://dx.doi.org/10.1002/adma.201204572DOI Listing
April 2013

Optimization of chemical structure of Schottky-type selection diode for crossbar resistive memory.

ACS Appl Mater Interfaces 2012 Oct 3;4(10):5338-45. Epub 2012 Oct 3.

WCU Hybrid Materials Program, Department of Materials Science and Engineering and Inter-university Semiconductor Research Center, Seoul National University, Seoul 151-744, Korea.

The electrical performances of Pt/TiO(2)/Ti/Pt stacked Schottky-type diode (SD) was systematically examined, and this performance is dependent on the chemical structures of the each layer and their interfaces. The Ti layers containing a tolerable amount of oxygen showed metallic electrical conduction characteristics, which was confirmed by sheet resistance measurement with elevating the temperature, transmission line measurement (TLM), and Auger electron spectroscopy (AES) analysis. However, the chemical structure of SD stack and resulting electrical properties were crucially affected by the dissolved oxygen concentration in the Ti layers. The lower oxidation potential of the Ti layer with initially higher oxygen concentration suppressed the oxygen deficiency of the overlying TiO(2) layer induced by consumption of the oxygen from TiO(2) layer. This structure results in the lower reverse current of SDs without significant degradation of forward-state current. Conductive atomic force microscopy (CAFM) analysis showed the current conduction through the local conduction paths in the presented SDs, which guarantees a sufficient forward-current density as a selection device for highly integrated crossbar array resistive memory.
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http://dx.doi.org/10.1021/am301293vDOI Listing
October 2012

One-dimensional TiO₂@Ag nanoarchitectures with interface-mediated implementation of resistance-switching behavior in polymer nanocomposites.

ACS Appl Mater Interfaces 2012 Nov 12;4(11):5727-31. Epub 2012 Nov 12.

A nanocomposite capable of showing a resistance-switching behavior is prepared using novel resistance-switchable fillers embedded in a polymer matrix. The filler in this study employs a conformal passivation layer of highly crystalline TiO₂ on surfaces of conductive Ag nanowires to effectively gate electron flows delivered through the conductive core, resulting in an excellent resistance-switching performance. A nanocomposite prepared by controlled mixing of the resistance-switchable nanowires with a polymer matrix successfully exhibited a resistance-switching behavior of highly enhanced reliability and a resistance on/off ratio, along with flexibility due to the presence of nanowires of a tiny amount. The advantages of our approach include a simple and low-cost fabrication procedure along with sustainable performances suitable for a resistance-switching random-access-memory application.
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http://dx.doi.org/10.1021/am301362fDOI Listing
November 2012

Impact of bimetal electrodes on dielectric properties of TiO2 and Al-doped TiO2 films.

ACS Appl Mater Interfaces 2012 Sep 16;4(9):4726-30. Epub 2012 Aug 16.

WCU Hybrid Materials Program, Department of Materials Science and Engineering and Inter-university Semiconductor Research Center, Seoul National University, Seoul 151-744, Korea.

Rutile structured Al-doped TiO(2) (ATO) and TiO(2) films were grown on bimetal electrodes (thin Ru/thick TiN, Pt, and Ir) for high-performance capacitors. The work function of the top Ru layer decreased on TiN and increased on Pt and Ir when it was thinner than ~2 nm, suggesting that the lower metal within the electrodes influences the work function of the very thin Ru layer. The use of the lower electrode with a high work function for bottom electrode eventually improves the leakage current properties of the capacitor at a very thin Ru top layer (≤2 nm) because of the increased Schottky barrier height at the interface between the dielectric and the bottom electrode. The thin Ru layer was necessary to achieve the rutile structured ATO and TiO(2) dielectric films.
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http://dx.doi.org/10.1021/am301094tDOI Listing
September 2012
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