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Electrical Double Layer Capacitance in a Graphene-embedded Al2O3 Gate Dielectric.

Ki Min B, Kim SK, Jun Kim S, Ho Kim S, Kang MA, Park CY, Song W, Myung S, Lim J, An KS - Sci Rep (2015)

Bottom Line: Graphene heterostructures are of considerable interest as a new class of electronic devices with exceptional performance in a broad range of applications has been realized.In this system, the enhanced capacitance of the hybrid structure can be understood by the formation of a space charge layer at the graphene/Al2O3 interface.The electrical properties of the interface can be further explained by the electrical double layer (EDL) model dominated by the diffuse layer.

View Article: PubMed Central - PubMed

Affiliation: Thin Film Materials Research Center, Korea Research Institute of Chemical Technology (KRICT), Yuseong P. O. Box 107, Daejeon 305-600, Republic of Korea.

ABSTRACT
Graphene heterostructures are of considerable interest as a new class of electronic devices with exceptional performance in a broad range of applications has been realized. Here, we propose a graphene-embedded Al2O3 gate dielectric with a relatively high dielectric constant of 15.5, which is about 2 times that of Al2O3, having a low leakage current with insertion of tri-layer graphene. In this system, the enhanced capacitance of the hybrid structure can be understood by the formation of a space charge layer at the graphene/Al2O3 interface. The electrical properties of the interface can be further explained by the electrical double layer (EDL) model dominated by the diffuse layer.

No MeSH data available.


Related in: MedlinePlus

Preparation and characterization of a graphene-embedded Al2O3 capacitor.(a) Schematic of the graphene-embedded Al2O3 capacitor fabrication process. (b) TEM cross-sectional image of the graphene-embedded Al2O3 capacitor. (c) Raman spectrum of graphene sheets as a function of the number of layers (single, bi-, and tri-layer). XPS spectra of (d) C 1s for graphene on Al2O3 and (e) Al 2p for Al2O3 layer on ITO.
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f1: Preparation and characterization of a graphene-embedded Al2O3 capacitor.(a) Schematic of the graphene-embedded Al2O3 capacitor fabrication process. (b) TEM cross-sectional image of the graphene-embedded Al2O3 capacitor. (c) Raman spectrum of graphene sheets as a function of the number of layers (single, bi-, and tri-layer). XPS spectra of (d) C 1s for graphene on Al2O3 and (e) Al 2p for Al2O3 layer on ITO.

Mentions: Figure 1a shows the fabrication process of a graphene-embedded metal-insulator-metal (MIM) capacitor. Al2O3 films were deposited on cleaned ITO-coated glass using the ALD process and the graphene was synthesized utilizing the same method as previous works (see Methods)27. The synthesized graphene was transferred onto the Al2O3 film by a poly(methyl methacrylate) (PMMA) assisted wet transfer method. The graphene was patterned by Al pre-patterning and subsequent O2 plasma etching. The lateral dimension of patterned graphene was 0.8 × 1.0 mm. On the transferred graphene, Al2O3 was deposited again through the ALD process. Finally, the top electrode (Cr/Au of 5 nm/70 nm) was deposited by thermal evaporation with a shadow mask for capacitance measurements. The chemical and structural characterization of Al2O3 and the interface properties between graphene and Al2O3 were investigated using X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and transmission electron microscopy (TEM). As shown in the cross-sectional TEM image (Fig. 1b), the thickness of Al2O3 films on ITO and graphene was about 40 nm, and a graphene sheet inserted in Al2O3 also was observed. Fig. 1c reveals Raman spectra of the single, bi-, and tri-layer graphene transferred onto Al2O3, clearly showing the graphene fingerprints, i.e., D-, G-, and 2D-bands. Because the intensity of the D-band was extremely small, the graphene was nearly defect-free and has a large domain size. We also confirmed the number of graphene layers through the ratio of 2D and G peaks (Supplementary Fig. S1a, b). After the formation of the Al2O3 layer onto graphene by ALD, highly-crystalline graphene was well-preserved, as confirmed by the intensity of the D-band (Supplementary Fig. S1c). The chemical identification of Al2O3 and graphene was carried out using XPS analysis. Figure 1d shows the C 1s core level spectra obtained from graphene on Al2O3, indicating that sp2 C-C bonds, a small C-O bond, and C = O bond were observed. Figure 1e exhibits a peak at 74 eV, corresponding to the Al 2p of Al2O3. These results reveal that the graphene and Al2O3 layers are well-formed. It is well known that the deposition of few nm-thick Al2O3 layers onto graphene by ALD is difficult because of the inert and hydrophobic surface of graphene. In our study, however, the 40 nm-thick Al2O3 layer was utilized for the formation of the Al2O3-graphene hybrid layer. In the formation of the Al2O3 layer on graphene, dangling bonds or functional groups on the graphene sheet can react with ALD precursors on the edges and defect sites, and Al2O3 layer was deposited uniformly by using these defects as staring nucleation sites. The uniformity of the top Al2O3 layer on graphene was examined by atomic force microscopy (AFM). The RMS roughness was about 0.305 nm, which was compared with Al2O3 on ITO (Supplementary Fig. S2).


Electrical Double Layer Capacitance in a Graphene-embedded Al2O3 Gate Dielectric.

Ki Min B, Kim SK, Jun Kim S, Ho Kim S, Kang MA, Park CY, Song W, Myung S, Lim J, An KS - Sci Rep (2015)

Preparation and characterization of a graphene-embedded Al2O3 capacitor.(a) Schematic of the graphene-embedded Al2O3 capacitor fabrication process. (b) TEM cross-sectional image of the graphene-embedded Al2O3 capacitor. (c) Raman spectrum of graphene sheets as a function of the number of layers (single, bi-, and tri-layer). XPS spectra of (d) C 1s for graphene on Al2O3 and (e) Al 2p for Al2O3 layer on ITO.
© Copyright Policy - open-access
Related In: Results  -  Collection

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Show All Figures
getmorefigures.php?uid=PMC4632157&req=5

f1: Preparation and characterization of a graphene-embedded Al2O3 capacitor.(a) Schematic of the graphene-embedded Al2O3 capacitor fabrication process. (b) TEM cross-sectional image of the graphene-embedded Al2O3 capacitor. (c) Raman spectrum of graphene sheets as a function of the number of layers (single, bi-, and tri-layer). XPS spectra of (d) C 1s for graphene on Al2O3 and (e) Al 2p for Al2O3 layer on ITO.
Mentions: Figure 1a shows the fabrication process of a graphene-embedded metal-insulator-metal (MIM) capacitor. Al2O3 films were deposited on cleaned ITO-coated glass using the ALD process and the graphene was synthesized utilizing the same method as previous works (see Methods)27. The synthesized graphene was transferred onto the Al2O3 film by a poly(methyl methacrylate) (PMMA) assisted wet transfer method. The graphene was patterned by Al pre-patterning and subsequent O2 plasma etching. The lateral dimension of patterned graphene was 0.8 × 1.0 mm. On the transferred graphene, Al2O3 was deposited again through the ALD process. Finally, the top electrode (Cr/Au of 5 nm/70 nm) was deposited by thermal evaporation with a shadow mask for capacitance measurements. The chemical and structural characterization of Al2O3 and the interface properties between graphene and Al2O3 were investigated using X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and transmission electron microscopy (TEM). As shown in the cross-sectional TEM image (Fig. 1b), the thickness of Al2O3 films on ITO and graphene was about 40 nm, and a graphene sheet inserted in Al2O3 also was observed. Fig. 1c reveals Raman spectra of the single, bi-, and tri-layer graphene transferred onto Al2O3, clearly showing the graphene fingerprints, i.e., D-, G-, and 2D-bands. Because the intensity of the D-band was extremely small, the graphene was nearly defect-free and has a large domain size. We also confirmed the number of graphene layers through the ratio of 2D and G peaks (Supplementary Fig. S1a, b). After the formation of the Al2O3 layer onto graphene by ALD, highly-crystalline graphene was well-preserved, as confirmed by the intensity of the D-band (Supplementary Fig. S1c). The chemical identification of Al2O3 and graphene was carried out using XPS analysis. Figure 1d shows the C 1s core level spectra obtained from graphene on Al2O3, indicating that sp2 C-C bonds, a small C-O bond, and C = O bond were observed. Figure 1e exhibits a peak at 74 eV, corresponding to the Al 2p of Al2O3. These results reveal that the graphene and Al2O3 layers are well-formed. It is well known that the deposition of few nm-thick Al2O3 layers onto graphene by ALD is difficult because of the inert and hydrophobic surface of graphene. In our study, however, the 40 nm-thick Al2O3 layer was utilized for the formation of the Al2O3-graphene hybrid layer. In the formation of the Al2O3 layer on graphene, dangling bonds or functional groups on the graphene sheet can react with ALD precursors on the edges and defect sites, and Al2O3 layer was deposited uniformly by using these defects as staring nucleation sites. The uniformity of the top Al2O3 layer on graphene was examined by atomic force microscopy (AFM). The RMS roughness was about 0.305 nm, which was compared with Al2O3 on ITO (Supplementary Fig. S2).

Bottom Line: Graphene heterostructures are of considerable interest as a new class of electronic devices with exceptional performance in a broad range of applications has been realized.In this system, the enhanced capacitance of the hybrid structure can be understood by the formation of a space charge layer at the graphene/Al2O3 interface.The electrical properties of the interface can be further explained by the electrical double layer (EDL) model dominated by the diffuse layer.

View Article: PubMed Central - PubMed

Affiliation: Thin Film Materials Research Center, Korea Research Institute of Chemical Technology (KRICT), Yuseong P. O. Box 107, Daejeon 305-600, Republic of Korea.

ABSTRACT
Graphene heterostructures are of considerable interest as a new class of electronic devices with exceptional performance in a broad range of applications has been realized. Here, we propose a graphene-embedded Al2O3 gate dielectric with a relatively high dielectric constant of 15.5, which is about 2 times that of Al2O3, having a low leakage current with insertion of tri-layer graphene. In this system, the enhanced capacitance of the hybrid structure can be understood by the formation of a space charge layer at the graphene/Al2O3 interface. The electrical properties of the interface can be further explained by the electrical double layer (EDL) model dominated by the diffuse layer.

No MeSH data available.


Related in: MedlinePlus