Byung Jin Cho

Korea Advanced Institute of Science and Technology , Sŏul, Seoul, South Korea

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Publications (174)490.46 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: A decade after the discovery of graphene flakes, exfoliated from graphite, we have now secured large scale and high quality graphene film growth technology via a chemical vapor deposition (CVD) method. With the establishment of mass production of graphene using CVD, practical applications of graphene to electronic devices have gained an enormous amount of attention. However, several issues arise from the interfaces of graphene systems, such as damage/unintentional doping of graphene by the transfer process, the substrate effects on graphene, and poor dielectric formation on graphene due to its inert features, which result in degradation of both electrical performance and reliability in actual devices. The present paper provides a comprehensive review of the recent approaches to resolve these issues by interface engineering of graphene for high performance electronic devices. We deal with each interface that is encountered during the fabrication steps of graphene devices, from the graphene/metal growth substrate to graphene/high-k dielectrics, including the intermediate graphene/target substrate.
    12/2015; 2(1). DOI:10.1186/s40580-015-0042-x
  • Onejae Sul · Jaehoon Bong · Alex Yoon · Byung Jin Cho
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    ABSTRACT: We report that oxygen plasma treatment of CVD-grown graphene can improve the integrity of an aluminum oxide layer deposited by atomic layer deposition. There is an optimum process window for treatment with O2 plasma which does not cause serious degradation in the quality of the graphene, but provides significant improvement in the gate dielectric integrity in relation to capacitance uniformity, leakage current, and dielectric breakdown voltage.
    Journal of Nanoscience and Nanotechnology 09/2015; 15(1). DOI:10.1166/jnn.2015.9058 · 1.56 Impact Factor
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    ABSTRACT: In this letter, we discuss the mechanism of Schottky barrier height (SBH) modulation of the TaN/Ge contact by varying the nitrogen concentration in the TaN. The Fermi level, which is strongly pinned near the valence band edge of Ge, moves to the conduction band edge of Ge with higher nitrogen concentration in the reactive sputtered TaN. This SBH modulation is attributed to the presence of an electric dipole induced by Ge–N bonds at the interface of the TaN/Ge contact. This SBH modulation due to the semiconductor-nitrogen bonds at the interface is not specific to TaN/Ge, but rather is a general feature in various transition-metal nitride systems on various semiconductors.
    IEEE Electron Device Letters 08/2015; 36(10). DOI:10.1109/LED.2015.2470535 · 2.75 Impact Factor
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    ABSTRACT: Sinusoidal wrinkles develop in compressively stressed film as a means to release stored elastic energy. Here, a simple way to fabricate large-area, periodic, hexagonal wrinkled pattern on nanocrystalline graphitic films grown on c-plane sapphire (<50 nm thick) by the spontaneous delamination–buckling of the as-grown film during cooling is reported. According to the continuum mechanics calculation, strain-relief pattern adopting the hexagonal wrinkled pattern has a lower elastic energy than that of the telephone cord wrinkle at thickness regime below 50 nm. A high-fidelity transfer method is developed to transfer the hexagonal wrinkled films onto arbitrary substrates. Nanoindentation studies show that hexagonal wrinkle film engineered this way may act as shock absorber. The hexagonal wrinkled carbon film is able to selectively promote the differentiation of human mesenchymal stem cell toward the osteogenic lineage in the absence of osteogenic inducing medium.
    Advanced Functional Materials 08/2015; DOI:10.1002/adfm.201502010 · 11.81 Impact Factor
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    ABSTRACT: We demonstrate Fermi-level unpinning and contact resistance reduction by surface passivation using SF6 plasma treatment of a metal/germanium (Ge) contact. A specific contact resistivity (ρc) of 1.14×10-3 Ω·cm2 and 0.31 eV of Schottky barrier height (SBH) are achieved for a Ti/SF6-treated n-type Ge (n-Ge) (Nd = 1×1017 cm-3) contact, exhibiting 1700 times ρc reduction from a Ti/non-treated n-Ge contact. A convenient and effective passivation process of the Ge surface is presented to alleviate Fermi-level pinning at metal/Ge contact and lower source/drain (S/D) contact resistance of Ge n-type field effect transistors (FET).
    IEEE Electron Device Letters 08/2015; 36(8):1-1. DOI:10.1109/LED.2015.2440434 · 2.75 Impact Factor
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    ABSTRACT: The chemical vapor deposition (CVD) of graphene on Cu substrates enables the fabrication of large-area monolayer graphene on desired substrates. However, during the transfer of the synthesized graphene, topographic defects are unavoidably formed along the Cu grain boundaries, degrading the electrical properties of graphene and increasing the device-to-device variability. Here, we introduce a method of hot-pressing as a surface pre-treatment to improve the thermal stability of Cu thin film for the suppression of grain boundary grooving. The flattened Cu thin film maintains its smooth surface even after the subsequent high temperature CVD process necessary for graphene growth, and the formation of graphene without wrinkles is realized. Graphene field effect transistors (FETs) fabricated using the graphene synthesized on hot-pressed Cu thin film exhibit superior field effect mobility and significantly reduced device-to-device variation.
    Nano Research 04/2015; 8(4):1075-1080. DOI:10.1007/s12274-014-0585-x · 7.01 Impact Factor
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    ABSTRACT: Insulating layers based on oxides and nitrides provide high capacitance, low leakage, high breakdown field and resistance to electrical stresses when used in electronic devices based on rigid substrates. However, their typically high process temperatures and brittleness make it difficult to achieve similar performance in flexible or organic electronics. Here, we show that poly(1,3,5-trimethyl-1,3,5-trivinyl cyclotrisiloxane) (pV3D3) prepared via a one-step, solvent-free technique called initiated chemical vapour deposition (iCVD) is a versatile polymeric insulating layer that meets a wide range of requirements for next-generation electronic devices. Highly uniform and pure ultrathin films of pV3D3 with excellent insulating properties, a large energy gap (>8 eV), tunnelling-limited leakage characteristics and resistance to a tensile strain of up to 4% are demonstrated. The low process temperature, surface-growth character, and solvent-free nature of the iCVD process enable pV3D3 to be grown conformally on plastic substrates to yield flexible field-effect transistors as well as on a variety of channel layers, including organics, oxides, and graphene.
    Nature Material 03/2015; 14(6). DOI:10.1038/nmat4237 · 36.50 Impact Factor
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    ABSTRACT: We report on the diffusion barrier properties of chemical-vapor-deposition grown graphene, graphene oxide, and reduced graphene oxide (rGO) for copper metallization in integrated circuits. Single-layer graphene shows the best diffusion barrier performance among the three but it has poor integration compatibility, displaying weak adhesion and poor nucleation for Cu deposition on top of it. Within the allowable thermal budget in the back-end-of-line process, rGO in a range of 1 nm thickness shows excellent thermal stability with suitable integration compatibility at 400 °C for 30 min. The diffusion barrier property was verified through optical, physical, and chemical analyses. The use of an extremely thin rGO layer as a Cu barrier material is expected to provide an alternative route for further scaling of copper interconnect technology.
    Applied Physics Letters 02/2015; 106(6):063112. DOI:10.1063/1.4908559 · 3.30 Impact Factor
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    ABSTRACT: We investigate the impact of metal-interfacial layer-semiconductor source/drain (M-I-S S/D) structure with heavily doped n-type interfacial layer (n+-IL) or with undoped IL on sub-10-nm n-type germanium (Ge) FinFET device performance using 3-D TCAD simulations. Compared to the metal- semiconductor S/D structure, the M-I-S S/D structures provide much lower contact resistivity. Especially, the M-I-S S/D structure with n+-IL provides much lower contact resistivity, resulting in ~5× lower contact resistivity than 1×10-8 Ω-cm2, specified in International Technology Roadmap for Semiconductors. In addition, we found that the M-I-S structure with n+-IL remarkably suppresses the sensitivity of contact resistivity to S/D doping concentration.
    IEEE Electron Device Letters 12/2014; 35(12):1185-1187. DOI:10.1109/LED.2014.2364574 · 2.75 Impact Factor
  • Ju Hyung We · Sun Jin Kim · Byung Jin Cho
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    ABSTRACT: TEG (Thermoelectric power generator) modules are attractive energy harvesters, as they can deliver electrical output power from the temperature difference of all sorts of things. Recently, growing interests in self-powered wearable mobile electronics provoke the necessity of flexible TEG modules. However, the technology on flexible TEG modules is still at a very early stage. Here we demonstrate flexible high-performance TEG modules using a screen-printed inorganic thermoelectric thick film and organic conducting polymer hybrid composite. By infiltrating the organic conducting polymer, poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS), into the micropores of the screen-printed thermoelectric thick film, the flexibility of the module is greatly enhanced without degradation of the output characteristics of the module. This work provides a promising new approach which has the potential to achieve a flexible high-performance TEG module.
    Energy 08/2014; 73:506–512. DOI:10.1016/ · 0.53 Impact Factor
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    ABSTRACT: A method of graphene transfer without metal etching is developed to minimize the contamination of graphene in the transfer process and to endow the transfer process with a greater degree of freedom. The method involves direct delamination of single-layer graphene from a growth substrate, resulting in transferred graphene with nearly zero Dirac voltage due to the absence of residues that would originate from metal etching. Several demonstrations are also presented to show the high degree of freedom and the resulting versatility of this transfer method.
    Small 08/2014; 11(2). DOI:10.1002/smll.201401196 · 8.37 Impact Factor
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    ABSTRACT: Layered structures of transition metal dichalcogenides stacked by van der Waals interactions are now attracting the attentions of many researchers because they have fascinating electronic, optical, thermoelectric and catalytic properties emerging at the monolayer limit. However, the commonly used methods for preparing monolayers have limitations of low yield and poor extendibility into large-area applications. Herein, we demonstrate the synthesis of large area MoSe2 with high quality and uniformity by selenization of MoO3 via chemical vapor deposition on arbitrary substrates such as SiO2 and sapphire. The resultant monolayer was intrinsically doped, as evidenced by the formation of charged excitons under low temperature photoluminescence analysis. A van der Waals heterostructure of MoSe2 on graphene was also demonstrated. Interestingly, the MoSe2/graphene heterostructures show strong quenching of the characteristic photoluminescence from MoSe2, indicating the rapid transfer of photo-generated charge carriers between MoSe2 and graphene. The development of highly controlled heterostructures of two dimensional materials will further advances in the physics and chemistry of reduced dimensional systems and will provide novel applications in electronics and optoelectronics.
    ACS Nano 07/2014; 8(7). DOI:10.1021/nn405685j · 12.88 Impact Factor
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    ABSTRACT: Crystallization of materials has attracted research interests for a long time, and its mechanisms in three-dimensional materials have been well studied. However, crystallization of two-dimensional (2D) materials is yet to be challenged. Clarifying the dynamics underlying growth of 2D materials will provide the insight for the potential route to synthesize large and highly crystallized 2D domains with low defects. Here we present the growth dynamics and recrystallization of 2D material graphene under a mobile hot-wire assisted chemical vapor deposition (MHW-CVD) system. Under the local but sequential heating by MHW-CVD system, the initial nucleation of nano-crystalline graphenes, which were not extended into the growth stage due to the insufficient thermal energy, took a recrystallization and converted into a grand single crystal domain. While this process, the stitching-like healing of graphene was also observed. The local but sequential endowing thermal energy to nano-crystalline graphenes enabled us to simultaneously reveal the recrystallization and healing dynamics in graphene growth, which suggests an alternative route to synthesize a highly crystalline and large domain size graphene. Also, this recrystallization and healing of 2D nano-crystalline graphenes offers an interesting insight on the growth mechanism of 2D materials.
    Nano Letters 06/2014; 14(8). DOI:10.1021/nl5012323 · 13.59 Impact Factor
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    ABSTRACT: We report a post-synthetic n-doping method for chemical-vapor-deposition (CVD) grown graphene using wet chemical processing. An ammonium fluoride solution was found effective in converting pristine hole doping into electron doping in addition to the mobility improvement of charge carriers. We verified the doping by electrical measurements, Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) analyses and suggest that the mechanism of n-doping is electrostatic doping by ionic physisorption of ammonium ions on the graphene surface. This simple chemical doping method provides a facile and robust route to n-doping of large area graphene for the realization of high performance graphene-based electronic devices.
    Nanoscale 06/2014; 6(15). DOI:10.1039/c4nr01160k · 7.39 Impact Factor
  • Sun Jin Kim · Ju Hyung We · Byung Jin Cho
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    ABSTRACT: The conversion of body heat into electrical energy using a thermoelectric (TE) power generator is useful for wearable self-powered mobile electronic systems such as medical sensors or smart watches. We herein demonstrate a glass fabric-based flexible TE generator using a screen printing technique and the self-sustaining structure of a TE device without top and bottom substrates. With this technique it is possible to make the device thin (similar to 500 mu m), lightweight (similar to 0.13 g cm(-2)), and flexible. In addition, the developed TE generator achieved an unprecedentedly large output power density which is several tens of times higher than that of flexible TE generators reported to date. The developed TE generator shows an allowable bending radius of as low as 20 mm and no change in performance by repeated bending for 120 cycles. This work can expedite the development of wearable self-powered mobile devices.
    Energy & Environmental Science 06/2014; 7(6):1959. DOI:10.1039/c4ee00242c · 20.52 Impact Factor
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    ABSTRACT: We demonstrate top-gate graphene field effect transistors (FETs) on an aluminum nitrite (AlN) substrate with high surface phonon energy. Electrical transport measurements reveal significant improvement of the carrier mobility of graphene FETs on AlN compared to those on SiO2. This is attributed to the suppression of surface phonon scattering due to the high surface phonon energy of the AlN substrate. The RF cut-off frequency of the graphene FET is also greatly increased when the AlN substrate is used. AlN can easily be formed on a Si or SiO2 substrate using a standard semiconductor process and thus provides a practical way to improve the performance of graphene FETs.
    Applied Physics Letters 05/2014; 104(19):193112-193112-4. DOI:10.1063/1.4878316 · 3.30 Impact Factor
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    ABSTRACT: We report an alternative approach to lower contact resistance and extend charge transfer length by forming graphene antidot arrays under metal electrode to introduce edge contact of graphene. The edge contact resistivity of ∼2.2 × 10−9 Ω·cm2 is experimentally estimated, based on the experiment and one-dimensional equivalent circuit model, and the result agrees well with the previous theoretical report. The proposed contact module structure can open alternative ways to overcome the poor contact performance and the current crowding effect at the metal-graphene contact.
    Applied Physics Letters 05/2014; 104(18):183506. DOI:10.1063/1.4875709 · 3.30 Impact Factor
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    ABSTRACT: A soft program method is proposed for charge-trap flash (CTF) memory devices. By adding a subsequent small positive gate pulse after main Fowler–Nordheim (FN) injection programming, early charge loss is greatly reduced. The multi-level cell performance as well as the initial flat-band voltage (VFB) instability can thereby be improved by removing the trapped electrons at the shallow traps in the blocking oxide layer. The proposed soft program method is a simple but very effective way to improve the fast retention property without changing the memory structure, especially for cases where the κ-value of the blocking oxide is high.
    Solid-State Electronics 04/2014; 94:86–90. DOI:10.1016/j.sse.2014.02.012 · 1.50 Impact Factor
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    ABSTRACT: We investigated the ultrafast carrier dynamics and phonon relaxation of CVD-grown monolayer and 9-layer graphene on a quartz substrate. Excitation was performed at 400 and 800 nm. The normalized change in optical density ΔOD was probed over the range 260–640 nm (1.94–4.77 eV), reaching down into the region of graphene’s Fano resonance, previously not investigated in femtosecond broadband pump–probe experiments. Time constants of 160 fs and 4 ps were found and assigned to carrier–optical phonon scattering and slower phonon relaxation processes, respectively. The carrier distribution at early times was clearly hotter for 400 nm excitation than for 800 nm excitation. A pronounced spectral bleach feature was observed below 300 nm. It immediately formed after photoexcitation and recovered slowly, with a time constant of 35 ps for monolayer and time constants of 120 and 970 ps for 9-layer graphene. The same dynamics were found for weak transient absorption features above 300 nm, which emerged after ca. 0.5 ps. The slow dynamics were assigned to interfacial heat flow from graphene to the quartz substrate. The bleach and absorption features were well described by a simple model assuming a red-shift of the Fano resonance. This red-shift disappeared with progressive cooling of graphene. We therefore suggest that the red-shift is induced by shrinking of the band separation due to lattice heating.
    The Journal of Physical Chemistry C 03/2014; 118(12):6454–6461. DOI:10.1021/jp4072197 · 4.77 Impact Factor
  • Seung Min Song · Jae Hoon Bong · Byung Jin Cho
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    ABSTRACT: Understanding of the contact between graphene and metal is a key issue to improve device performance. We extend the previous finding of work function pinning of monolayer graphene under various metals to multilayer graphene and discover that the work function of graphene under metal can be tuned from 4.3 eV to 5.1 eV by controlling the number of graphene layers. The work function of graphene is found to gradually shift with the number of graphene layers and four layers of graphene successfully screen this shift. These findings provide an alternative approach to control the work function of graphene electrodes.
    Applied Physics Letters 02/2014; 104(8):083512-083512-3. DOI:10.1063/1.4866337 · 3.30 Impact Factor

Publication Stats

2k Citations
490.46 Total Impact Points


  • 2008–2014
    • Korea Advanced Institute of Science and Technology
      • Department of Electrical Engineering
      Sŏul, Seoul, South Korea
  • 2007–2008
    • National University of Singapore
      • Department of Electrical & Computer Engineering
      Tumasik, Singapore
  • 2004
    • National Chiao Tung University
      • Department of Electronics Engineering
      Hsinchu, Taiwan, Taiwan
    • Institute of Microelectronics
      Tumasik, Singapore
    • National Tsing Hua University
      • Department of Electronic Engineering
      Hsin-chu-hsien, Taiwan, Taiwan
  • 2003–2004
    • University of Texas at Austin
      • Department of Electrical & Computer Engineering
      Austin, Texas, United States