• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2010년도 추계학술대회 논문집
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• pp.369-370
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• 2010

• 센서학회지
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• 제27권3호
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• pp.204-208
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• 2018

Monolayer graphene grown via chemical vapor deposition (CVD) is recognized as a promising material for sensor applications owing to its extremely large surface-to-volume ratio and outstanding electrical properties, as well as the fact that it can be easily transferred onto arbitrary substrates on a large-scale. However, the Dirac voltage of CVD-graphene devices fabricated with transferred graphene layers typically exhibit positive shifts arising from transfer and photolithography residues on the graphene surface. Furthermore, the Dirac voltage is dependent on the channel lengths because of the effect of metal-graphene contacts. Thus, large and nonuniform Dirac voltage of the transferred graphene is a critical issue in the fabrication of graphene-based sensor devices. In this work, we propose a fabrication process for graphene field-effect transistors with Dirac voltages close to zero. A vacuum annealing process at $300^{\circ}C$ was performed to eliminate the positive shift and channel-length-dependence of the Dirac voltage. In addition, the annealing process improved the carrier mobility of electrons and holes significantly by removing the residues on the graphene layer and reducing the effect of metal-graphene contacts. Uniform and close to zero Dirac voltage is crucial for the uniformity and low-power/voltage operation for sensor applications. Thus, the current study is expected to contribute significantly to the development of graphene-based practical sensor devices.

• 한국재료학회:학술대회논문집
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• 한국재료학회 2012년도 춘계학술발표대회
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• pp.69.3-69.3
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• 2012

A high-performance low-voltage graphene field-effect transistor (FED array was fabricated on a flexible polymer substrate using solution-processable, high-capacitance ion gel gate dielectrics. The high capacitance of the ion gel, which originated from the formation of an electric double layer under the application of a gate voltage, yielded a high on-current and low voltage operation below 3 V. The graphene FETs fabricated on the plastic substrates showed a hole and electron mobility of 203 and 91 $cm^2/Vs$, respectively, at a drain bias of - I V. Moreover, ion gel gated graphene FETs on the plastic substrates exhibited remarkably good mechanical flexibility. This method represents a significant step in the application of graphene to flexible and stretchable electronics.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2012년도 제43회 하계 정기 학술대회 초록집
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• pp.67-67
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• 2012

Graphene, two-dimensional one-atom-thick planar sheet of carbon atoms densely packed in a honeycomb crystal lattice, exhibits fascinating electrical properties, such as a linear energy dispersion relation and high mobility in addition to a wide-range optical absorption and high thermal conductivity. Graphene's outstanding tensile strength allows graphene-based electronic and photonic devices to be flexible, bendable, or even stretchable. Recently many groups have reported high performance electronic and optoelectronic devices based on graphene materials, i.e. field-effect transistors, gas sensors, nonvolatile memory devices, and plasmonic waveguides, in which versatile properties of graphene materials have been incorporated into a flexible electronic or optoelectronic platform. However, there are several fundamental or technological hurdles to be overcome in real applications of graphene in electronics and optoelectronics. In this tutorial we will present a short introduction to the basic material properties and recent progresses in applications of graphene to electronics and optoelectronics and discuss future outlook of graphene-based devices.

• 통합자연과학논문집
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• 제2권4호
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• pp.280-284
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• 2009

The unique electronic property of graphene sheets provides potential applications in nanocomposites and fabricating various nicroelectrical devices, such as field-effect transistors, ultrasensitive sensors, and electromechanical resonators. Several effective techniques have been developed for preparing graphene sheets. Among these technique, mechanical exfoliation can produce pure graphene and epitaxial graphene sheets have been prepared by treatment of silicon carbide wafers at high temperature. Recently, graphene sheets have been developed by chemical reduction method from graphene oxide. In this work, we have synthesized graphene sheets based on mechanical exfoliation and chemical reduction methods. Graphene sheets were characterized by field-effect scanning electron microscope (FE-SEM). The size of graphene sheets was from few hundreds nanometer to decades micrometer.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2011년도 제41회 하계 정기 학술대회 초록집
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• pp.121-121
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• 2011

Graphene formed by chemical vapor deposition was exposed to the various plasmas of Ar, O2, N2, and H2 to examine its effects on the bonding properties of graphene to metal. Upon the Ar plasma exposure of patterned graphene, the subsequently deposited metal electrodes remained intact, enabling successful fabrication of field effect transistor (FET) arrays. The effects of enhancing adhesion between graphene and metals were more evident from O2 plasmas than Ar, N2, and H2 plasmas, suggesting that chemical reaction of O radicals induces hydrophilic property of graphene more effectively than chemical reaction of H and N radicals and physical bombardment of Ar ions. From the electrical measurements (drain current vs. gate voltage) of field effect transistors before and after Ar plasma exposure, it was confirmed that the plasma treatment is very effective in controlling bonding properties of graphene to metals accurately without requiring buffer layers.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2012년도 제42회 동계 정기 학술대회 초록집
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• pp.578-578
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• 2012

Graphene, a flat one-atom-thick two-dimensional layer of carbon atoms, is considered to be a promising candidate for nanoelectronics due to its exceptional electronic properties. Most of all, future nanoelectronics such as flexible displays and artificial electronic skins require low cost manufacturing process on flexible substrate to be integrated with high resolutions on large area. The solution based printing process can be applicable on plastic substrate at low temperature and also adequate for fabrication of electronics on large-area. The combination of printed electronics and graphene has allowed for the development of a variety of flexible electronic devices. As the first step of the study, we prepared the gate electrodes by printing onto the gate dielectric layer on PET substrate. We showed the performance of graphene field-effect transistor with electrohydrodynamic (EHD) inkjet-printed Ag gate electrodes.

• 전자공학회논문지
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• 제53권2호
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• pp.117-122
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• 2016

최근 환경, 의료분야에서 실시가 검출 및 인체 삽입형 pH 센서에 대한 요구가 증가하고 있다. 이에 본 연구에서는 생체적 합성이 우수한 그래핀을 이용하여 실시간 pH 검출이 가능한 센서를 개발하였다. Polyethylene terephthalate(PET) 기판에 전사된 그래핀 표면에 이온 용액속에서 동작하는 전계효과 트랜지스터(solution-gated field-effect transistors; SGFETs)를 제작하였으며 이를 이용하여 이온 용액의 pH를 검출하였다. 제작한 트랜지스터의 게이트 채널 길이는 $500{\mu}m$, 게이트 채널 폭은 8mm이다. 이온 용액속에서 트랜지스터 동작특성 및 pH 감도를 평가하기 위하여 드레인-소스 전압($V_{DS}$)에 따른 드레인-소스 전류($I_{DS}$) 및 게이트-소스 전압($V_{GS}$)에 따른 드레인-소스 전류($I_{DS}$)를 측정하였다. PET기판에 전사된 그래핀 위에 제작한 그래핀 SGFETs의 전류-전압 특성은 이온 용액내에서 매우 안정적으로 동작하였으며 그래핀 SGFETs의 Dirac point는 이온 용액의 pH값이 증가함에 따라 양의 방향으로 19.32 mV/pH씩 증가하였다.

• 접착 및 계면
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• 제22권4호
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• pp.153-157
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• 2021

이차원 탄소 동소체인 그래핀은 기존 재료보다 우수한 기계적, 전기적 특성을 지니고 있다. 특히, 그래핀의 전하이동도는 실리콘 대비 100배가량 높다고 알려져 차세대 전자소자의 핵심재료로 각광을 받고 있다. 하지만, 그래핀은 외부 환경의 변화에 매우 민감하여 수분 혹은 산소에 취약하여 그래핀 기반 전자소자의 안정성이 취약하다는 단점이 존재하기에 이를 해결하기 위해 다양한 시도가 이뤄지고 있다. 본 연구에서는 그래핀 전계효과 트랜지스터의 절연막을 전사시에 사용되는 고분자 층의 표면 에너지를 조절하여 안정성을 크게 향상시키는 연구를 수행하였다. 절연층으로 쓰인 고분자의 표면 에너지가 낮아짐에 따라 물 분자 혹은 산소와 같은 대기중의 불순물 흡착을 효과적으로 제어함으로써, 안정성을 향상시킬 수 있었다.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2011년도 제40회 동계학술대회 초록집
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• pp.482-483
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• 2011

Graphene is a good candidate for the future nano-electronic materials because it has excellent conductivity, mobility, transparency, flexibility and others. Until now, most graphene researches are focused on the nano electronic device applications, however, biological application of graphene has been relatively less reported. We have fabricated a deoxyribonucleic acid (DNA) conjugated graphene field-effect transistor (FET) and measured the electrical transport characteristics. We have used graphene sheets grown on Ni substrates by chemical vapour deposition. The Raman spectra of graphene sheets indicate high quality and only a few number of layers. The synthesized graphene is transferred on top of the substrate with pre-patterned electrodes by the floating-and-scooping method [1]. Then we applied adhesive tapes on the surface of the graphene to define graphene flakes of a few micron sizes near the electrodes. The current-voltage characteristic of the graphene layer before stripping shows linear zero gate bias conductance and no gate operation. After stripping, the zero gate bias conductance of the device is reduced and clear gate operation is observed. The change of FET characteristics before and after stripping is due to the formation of a micron size graphene flake. After combined with 30 base pairs single-stranded poly(dT) DNA molecules, the conductance and gate operation of the graphene flake FETs become slightly smaller than that of the pristine ones. It is considered that DNA is to be stably binding to the graphene layer due to the ${\pi}-{\pi}$ stacking interaction between nucleic bases and the surface of graphene. And this binding can modulate the electrical transport properties of graphene FETs. We also calculate the field-effect mobility of pristine and DNA conjugated graphene FET devices.