• Journal of the Microelectronics and Packaging Society
• /
• v.30 no.2
• /
• pp.60-64
• /
• 2023

In this study, the electrical contact resistance characteristics between graphene and metals, which is one of important factors for the performance of graphene-based devices, were compared. High-quality graphene was synthesized by chemical vapor deposition (CVD) method, and Al, Cu, Ni, and Ti as electrode materials were deposited on the graphene surface with equal thickness of 50 nm. The contact resistances of graphene transferred to SiO₂/Si substrates and metals were measured by the transfer length method (TLM), and the average contact resistances of Al, Cu, Ni, and Ti were found to be 345 Ω, 553 Ω, 110 Ω, and 174 Ω, respectively. It was found that Ni and Ti, which form chemical bonds with graphene, have relatively lower contact resistances compared to Al and Cu, which have physical adsorption properties. The results of this study on the electrical properties between graphene and metals are expected to contribute to the realization of high-performance graphene-based devices including electronics, optoelectronic devices, and sensors by forming low contact resistance with electrodes.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2016.02a
• /
• pp.287.2-287.2
• /
• 2016

Silicon has considerably good characteristics on electron, hole mobility and its price. With 2-D sinlge-layer Graphene/n-Si heterojunction solar cell shows that in one sun condition exhibit power conversion efficiency(PCE) of 10.1%. This photovoltaic effect was achieved by applying gate voltage to the Schottky junction of the heterostructure solar cell. Energy band diagram shows that Schottky barrier between Si and graphene can be adjust by the external electric field. because of the fermi level of the graphene can be changed by external gate voltage, we can control the Schottkky barrier of the heterostructure solar cell. The ratio between generated power of solar cell and consumption electrical power is remarkable. Since we use the graphene as the top gate electrode, most of the sun light can penetrate into the active area.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2013.02a
• /
• pp.618-618
• /
• 2013

Graphene is only one atom thick planar sheet of sp2-bonded carbon atoms arranged in a honeycomb crystal lattice, which has flexible and transparent characteristics with extremely high mobility. These noteworthy properties of graphene have given various applicable opportunities as electrode and/or channel for various flexible devices via suitable physical and chemical modifications. In this work, for the development of all-graphene devices, we performed to synthesize alternately patterned structure of mono- and multi-layer graphene by using the patterned Ni film on Cu foil, having much different carbon solid solubilities. Depending on the process temperature, Ni film thickness, introducing occasion of methane and gas ratio of CH4/H2, the thickness and width of the multi-layer graphene were considerably changed, while the formation of monolayer graphene on just Cu foil was not seriously influenced. Based on the alternately patterned structure of mono- and multi-layer graphene as a channel and electrode, respectively, the flexible TFT (thin film transistor) on SiO2/Si substrate was fabricated by simple transfer and O2 plasma etching process, and the I-V characteristics were measured. As comparing the change of resistance for bending radius and the stability for a various number of repeated bending, we could confirm that multi-layer graphene electrode is better than Au/Ti electrode for flexible applications.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2012.08a
• /
• pp.112-112
• /
• 2012

Graphene has been considered as one of the potential post Si-materials due to its high mobility. [1] However, since graphene is semi-conductor with zero band gap, it is difficult to achieve high Ion/Ioff ratio, one of the most important requirements for commercial devices. There have been many attempts to open its band gap for high Ion/Ioff ratio, but most of them end up lowering the mobility. [2-5] Thus, we proposed and demonstrated a new device structure for graphene transistor based on one of the unique properties of graphene for high Ion/Ioff: using this approach, we were able to achieve the ratio over $10^5$. [6] Our device has several major advantages over previously proposed graphene based electronic devices. Since our device does not alter the given properties of graphene, such as opening the band gap, it has no fundamental issues on mobility degradations. In addition, our device is fully compatible with current Si technology and we were able to fabricate the devices with 6 inch wafer scale with CVD (Chemical Vapor Deposition) grown graphene. In this presentation, we will discuss about the details of our graphene device including the device structure and the detailed understanding of working mechanism. We will present device characteristics including I-V curves with $10^5$ on/off ratio. We will also present the performance of an inverter based on our devices. Finally, we will discuss the current issues and their potential solutions.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2014.02a
• /
• pp.273.1-273.1
• /
• 2014

Graphene, a two dimensional plane structure of $sp^2$ bonding, has been promised for a new material in many scientific fields such as physics, chemistry, and so on due to the unique properties. Chemical vapor deposition (CVD) method using transitional metals as a catalyst can synthesize large scale graphene with high quality and transfer on other substrates. However, it is difficult to control the number of graphene layers. Therefore, it is important to manipulate the number of graphene layers. In this work, homogeneous solid solution of Cu and Ni was used to control the number of graphene layers. Each films with different thickness ratio of Cu and Ni were deposited on $SiO_2/Si$ substrate. After annealing, it was confirmed that the thickness ratio accords with the composition ratio by X-ray diffraction (XRD). The synthesized graphene from CVD was analyzed via raman spectroscopy, UV-vis spectroscopy, and 4-point probe to evaluate the properties. Therefore, the number of graphene layers at the same growth condition was controlled, and the correlation between mole fraction of Ni and the number of graphene layers was investigated.

• Journal of Sensor Science and Technology
• /
• v.21 no.6
• /
• pp.425-428
• /
• 2012

This paper presents the fabrication and characterization of graphene based hydrogen sensors. Graphene was synthesized by annealing process of Ni/3C-SiC thin films. Graphene was transferred onto oxidized Si substrates for fabrication of chemiresistive type hydrogen sensors. Au electrode on the graphene shows ohmic contact and the resistance is changed with hydrogen concentration. Nanoparticle catalysts of Pd and Pt were decorated. Response factor and response (recovery) time of hydrogen sensors based on the graphene are improved with catalysts. The response factors of pure graphene, Pt and Pd doped graphenes are 0.28, 0.6 and 1.26, respectively, at 50 ppm hydrogen concentration.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2011.02a
• /
• pp.458-458
• /
• 2011

Graphene, a single atomic layer of sp2-bonded carbon, shows substantial potential for various applications. Chemical manipulation of its electronic properties will be of great importance. In this study, we have investigated interaction between graphene and organic molecular layer of tetrafluorotetracyanoquinodimethane (F4-TCNQ), a strong electron acceptor. F4-TCNQ films of varying thickness were evaporated onto graphene mechanically exfoliated on SiO2/Si substrates. F4-TCNQ molecules increase the frequencies of Raman G and 2D bands of graphene while decreasing the linewidth of G band and 2D/G intensity ratio, which is consistent with increase of hole density in graphene. These results exemplify the possibility of chemical tuning of electronic properties of graphene.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2010.02a
• /
• pp.368-368
• /
• 2010

Monolayers of graphite can be grown by fine controlled surface graphitization on the surfaces of various metallic and semiconducting materials. Epitaxial graphene grown on polished silicon carbide crystal surfaces has drawn much attention due to well known vacuum annealing procedures from surface analysis methods, especially scanning tunneling microscopy(STM) and scanning tunneling spectroscopy(STS). In this study, we have grown single layer and few layer graphene on silicon terminated 6H-SiC(0001) crystals. The growth of graphene layers were observed by low energy electron diffraction(LEED) patterns. Scanning tunneling microscopy and spectroscopy measurements were performed to illustrate the electronic structure which may display some clue on the influence of the underlying structure. Spatially resolved STS results acquired at the edges of epitaxial graphene show in detail the electron density of states, which is compared to theoretical calculations. STM measurements were also done on graphene films grown by chemical vapor deposition(CVD) and transferred onto a SiC(0001) crystal. These observations may provide a hint for the understanding of carrier scattering at the edges.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2012.08a
• /
• pp.318-318
• /
• 2012

A graphene layer is most important materials in resent year to enhance the electrical properties of semiconductor device due to high mobility, flexibility, strong mechanical resistance and transparency[1,2]. The resistance switching memory with the graphene layer have been reported for next generation nonvolatile memory device[3,4]. Also, the graphene layer is able to improve the electrical properties of memory device because of the high mobility and current density. In this study, the resistance switching memory device with metal-oxide nano-particles embedded in polyimide layer on the graphene mono-layer were fabricated. At first, the graphene layer was deposited $SiO_2$/Si substrate by using chemical vapor deposition. Then, a biphenyl-tetracarboxylic dianhydride-phenylene diamine poly-amic-acid was spin coated on the deposited metal layer on the graphene mono-layer. Then the samples were cured at $400^{\circ}C$ for 1 hour in $N_2$ atmosphere after drying at $135^{\circ}C$ for 30 min through rapid thermal annealing. The deposition of aluminum layer with thickness of 200 nm was done by a thermal evaporator. The electrical properties of device were measured at room temperature using an HP4156a precision semiconductor parameter analyzer and an Agilent 81101A pulse generator. We will discuss the switching mechanism of memory device with metal-oxide nano-particles on the graphene mono-layer.

• Journal of Electrochemical Science and Technology
• /
• v.15 no.2
• /
• pp.291-298
• /
• 2024

Due to its high theoretical capacity, Silicon (Si) has shown great potential as an anode material for lithium-ion batteries (LIBs). However, the large volume change of Si during cycling leads to poor cycling stability and low Coulombic efficiency. In this study, we synthesized Si/Carbon C45:Graphene composites using a ball-milling method with a fixed Si content (20%) and investigated the influence of the C45/Gr ratio on the electrochemical performance of the composites. The results showed that carbon C45 networks can provide good conductivity, but tend to break at Si locations, resulting in poor conductivity. However, the addition of graphene helps to reconnect the broken C45 networks, improving the conductivity of the composite. Moreover, the C45 can also act as a protective coating around Si particles, reducing the volume expansion of Si during charging/discharging cycles. The Si/C45:Gr (70:10 wt%) composite exhibits improved electrochemical performance with high capacity (~1660 mAh g^-1 at 0.1 C) and cycling stability (~1370 mAh g^-1 after 100 cycles). This work highlights the effective role of carbon C45 and graphene in Si/C composites for enhancing the performance of Si-based anode materials for LIBs.