Atomic-Layer-Deposition Growth of an Ultrathin HfO2 Film on

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Atomic-Layer-Deposition Growth of Ultra-Thin HfO2 Film on Graphene Meng-Meng Xiao, Chenguang Qiu, Zhiyong Zhang, and Lianmao Peng ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.7b09408 • Publication Date (Web): 13 Sep 2017 Downloaded from http://pubs.acs.org on September 16, 2017

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ACS Applied Materials & Interfaces

Atomic-Layer-Deposition Growth of Ultra-Thin HfO2 Film on Graphene Mengmeng Xiao, Chenguang Qiu, Zhiyong Zhang* and Lian-Mao Peng* Key Laboratory for the Physics and Chemistry of Nanodevices and Department of Electronics, Peking University, Beijing 100871, China.

ABSTRACT: Direct growth of ultra-thin gate dielectric layer with high uniformity and high quality on graphene remains a challenge for developing graphene-based transistors due to the chemical inert surface properties of graphene. Here we develop a method to realize atomic-layer-deposition (ALD) growth of ultra-thin high-κ dielectric layer on graphene through pre-modifying graphene surface using electron beam irradiation. An amorphous carbon layer induced by electron beam scanning is formed on graphene, and then acts as seed for ALD growth of high-κ dielectrics. Uniform HfO2 layer with equivalent oxide thickness (EOT) of 1.3 nm was grown as gate dielectric for top-gate graphene field effect transistors (FETs). The achieved gate capacitance is up to 2.63 µF/cm2, which is the highest gate capacitance on graphene solid state device to-date. In addition, the fabricated top-gate graphene FETs present high carrier mobility of up to 2500 cm2/V.s and negligible gate leakage current of down to 0.1 mA/cm2, showing that the ALD grown HfO2 dielectric layer is highly uniform and of very high quality.

KEYWORDS: Atomic layer deposition, HfO2, Graphene, high-κ, Gate insulator

ACS Paragon Plus Environment


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INTRODUCTION In the past two decades, sp2 carbon based nanomaterials, including graphene1 and carbon nanotube (CNT)2, have attracted intensive research interests especially in electronic applications. Owning to their high carrier mobility, high saturation velocity and ultra-thin body, graphene and CNT has been considered as excellent channel materials to construct high-performance field-effect transistors (FETs) under sub-10 nm technology node for future electronics3. The sp2 carbon skeleton structure contributes to the excellent electronic property and stability for graphene and CNT with atomic thickness, but brings a problem in fabricating gate dielectric layer for high-performance FETs. The lack of dangling bonds in graphene/CNT surface means no nuclear centers exist on high quality graphene surface to initiate atomic layer deposition (ALD) growth of high quality high-κ dielectric, and thus the preparation of ultra-thin gate dielectric on pristine CNT/graphene,such as through the mainstreaming ALD growth method, becomes a challenge for the development of carbon-based high performance nanoelectronic devices.

High-quality gate stack is one of the key components for high-performance FETs based on any semiconducting materials, graphene and CNT are not exception. Various methods have been proposed and investigated aiming to address the dielectric growth problems for carbon based nanomaterials. One alternative solution is to perform the ALD process on the gate metal itself and then aligned it on the top of graphene channel4-6. Methods based on this idea can avoid damaging the graphene’s original properties, while an extra transfer or physical assembly process is needed to align the top gate. Other methods to directly grow uniform high-κ film on graphene/CNT are through pre-building nucleation sites via surface treatments or introduction of interfacial layer before ALD growth. These methods include oxidized metal particle7, perylene tetracarboxylic acid (PTCA)8, DNA molecule9, thick polymer layer10, N2 plasma11, NO212 or O313 functionalization. The introduction of interfacial layer and pre-treatments increases not only the equivalent total oxide thickness (EOT) of the dielectric layers, but also leads to extra scattering or doping brought by the


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functionalization molecules. In addition, the heterogeneous gate oxide often brings instability problem via such processes as diﬀusion of precursors into the bulk of the polymer and growth inside the dielectric film 14. We reported earlier that high quality Y2O3 films could be uniformly grown on graphene via evaporating yttrium film followed by thermal oxidation15-17. However, Y2O3 film grown by this method cannot provide desired surface conformal coverage, which is highly desirable for fabricating state-of-the-art vertical channel transistors such as Fin-FETs18. Meanwhile, high-κ dielectric layer with small EOT and high uniformity is especially necessary to suppress short channel effect (SCE)

19, 20

. As the mainstreaming method to prepare

high- κ dielectric layer in modern transistor fabrication technology, ALD can grow high quality high- κ dielectric due to its precise thickness controllability, excellent surface conformal coverage, high film quality and uniformity, low deposition temperatures19, 20, and is thus the preferred method to grow high quality dielectric layer on channel materials.

In this work, we develop an efficient method to realize ALD growth of ultra-thin high- κ dielectric layer on graphene by using electron beam irradiation to pre-modify graphene surface. An amorphous carbon layer is formed on graphene, induced by electron beam scanning, and acts as the seeds for ALD growth of high- κ dielectrics. Uniform HfO2 layer with EOT of 1.3 nm is grown as gate dielectric for top-gate graphene FETs, and the achieved gate capacitance is up to 2.63μF/cm2, which is the record of gate capacitance on graphene solid state device to-date. In addition, the fabricated top-gate graphene FETs present high carrier mobility of up to 2500 cm2/V.s and negligible gate leakage current of down to 0.1 mA/cm2, indicating high quality and high uniformity of the ALD grown HfO2 dielectric layer on graphene.

RESULTS AND DISCUSSION Chemical vapor deposition (CVD) grown graphene was used in this work, which was grown on Pt foil at 1070°C and then transferred to the SiO2/Si substrate by a



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well-developed bubbling transfer method22, 23. After an annealing process in Ar/H2 at 350°C for 30min, graphene sample with clean surface was ready to grow high-κ dielectric. Figure 1a shows two atomic force microscopic (AFM) images of ALD grown HfO2 on graphene samples with and without electron beam irradiation (EBI) pre-modification. The blue lines in the inset show the height profile which confirms the conformal growth of HfO2 on the EBI modification graphene. HfO2 films were grown on two kinds of graphene samples simultaneously with thickness of approximately 4 nm (See Figure S1 in Supporting Information), which was controlled by growth cycles (35 cycles) during ALD process. For the pristine graphene, only islands of HfO2 were observed with a roughness of approximately 1.7 nm (see Fig. S3b in Supporting Information) and no compact HfO2 film was observed, and these results are consistent with earlier reports8. This is because for a high quality graphene, there exist no continuous nuclear centers for ALD growth on graphene. As a contrast, uniform and compact HfO2 film with a roughness of 0.4 nm (Fig. S3c) was observed on the graphene pre-modified by EBI. The EBI modification process was performed inside a field emission SEM chamber with an oil pump, which may induce a very thin layer of amorphous carbon on the sample during electron beam scanning. The amorphous carbon may come from the contamination from the oil pump system or other organic contamination in the SEM chamber, and is usually composed of sp2 and sp3 bonds

24, 25

. Therefore, the thin amorphous carbon layer can thus act as nuclear

centers for ALD growth of HfO2 film on graphene.

Figure 1b shows two Raman spectra of graphene before and after EBI modification. The intensity ratio of G peak and 2D peak is about 0.5, indicating that the graphene used here is monolayer. The negligible intensity of D peak observed in the Raman spectrum obtained from pristine graphene suggests that that the graphene is of low defect density. On the other hand, after EBI modification, there appears a D peak at 1345cm-1, which might arise from the EBI induced damages24, 25 or amorphous carbon on graphene28. However, in this work, a low energy (1.5 keV) electron beam was used to modify graphene to avoid knock-on damage to carbon atoms in graphene, which


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starts at 80keV29. Therefore, the D-band peak observed in low energy EBI modified graphene is mainly originated from amorphous carbon,which is consistent with a recent report in Ref. [28].

Since it is induced by EBI, the density of amorphous carbon on graphene is proportional to electron dose of EBI. To further verify the effect of EBI modification for ALD-growth on graphene, we explored how irradiation dose of electron-beam affects the HfO2 film growth process on graphene. The electron beam dose in a SEM can be readily adjusted by varying spot size, scan area (magnification) and scan time. Here we adjusted irradiation dose through varying scan time while fixing other parameters. Shown in Fig. 1c are SEM images of ALD grown HfO2 films (35cycles) on graphene regions that were modified by EBI with scanning time of 0s, 15s, 60s and 120s respectively. The relationship of electron beam dose and scanning time was estimated in the supporting information (Fig. S4). Only sparse HfO2 particles were formed on pristine graphene without EBI modification (i.e. scan time is 0s). The density of HfO2 particles increased significantly with scan time, and continuous film without visible pinhole emerged when scanned by 120s. Figure 1d shows that the corresponding leakage current of the HfO2 film on graphene decreases with increasing EBI scan time, indicating that the compactness of HfO2 film increases with the quantity of deposited amorphous carbon. The 4 nm HfO2 film on the graphene modified by EBI with scan time of 120 s reduced current leakage down to 0.1 mA/cm2, which is an order of magnitude lower than the leakage standard (1 mA/cm2) for ultra-low-power (ULP) applications20, 30. Therefore, EBI modification can help to realize ultra-thin uniform HfO2 or other high- κ dielectric on graphene or CNT through ALD-growth. Furthermore, new instruments can be designed to perform EBI modification on graphene with large area, and then provide a high-efficiecny assistant method to realize ALD-growth on graphene.

To further characterize the HfO2 film grown by EBI assistanted ALD as gate dielectric for carbon transistors, we integrated the film into top-gate graphene FETs Top-gate



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graphene FETs were fabricated according to the process flow shown in Fig. 2, in which the EBI dose was fixed by using scan time of 120s. Figure 3a shows how EBI affects the transfer curve of a back-gate graphene FET. Before EBI, the transfer curve of a typical FET is similar to that of previously reported back-gate graphene FETs

16,

22

. The field-effect carrier mobility of the pristine graphene, retrieved from transfer

curves via the well-developed fitting model31, is approximately 3300 cm2/v·s for holes and 3500 cm2/v·s for electrons (see Fig. S2 in Supporting Information). The back-gate FETs measured in air in a few days after the device fabrication (black curve in Fig.3a) showed a positive Dirac point voltage (16.4 V), indicating a light p-type doping induced by oxygen and water molecule adsorption from air 31. After EBI, the transfer curve of the back gate graphene FET was immediately measured (blue curve in Fig. 3a), and showed a drastic change compared with that of the pristine one. The Dirac point voltage shifts to a negative value (-8.4V), which is typical of n-doping device as a result of positive charge accumulation in SiO2 substrate. It is well known that low energy electron beam irradiation will induce emission of secondary electron from SiO2/Si substrate and leave fixed positive charge centers in SiO2 32. These remained positive charge centers in/around graphene channel will induce Coulomb scattering for carriers, and induce significant current degradation. In addition, the Dirac point voltage is shifting back to positive direction when the device was exposed to air, and meanwhile the current increases with exposure time as shown in Fig. 3a. This is because the positive charge centers are gradually recovered by absorbing O2 or water molecules from air 33. After a long time recovery in air, for example 4 weeks (green curve in Fig. 3a), the EBI modified graphene FET was observed to have fully recovered back to its original performance before modification. The ALD process during top-gate graphene FET fabrication is helpful for the recovery of EBI injury ( Fig.S5 in Supporting information) owing to the high-temperature and water-rich condition of the ALD process. Therefore, EBI modification on graphene FETs induces mainly temporary and recoverable performance degradation which can be repaired through certain treatment process or just exposing in air for a long time. Figure 3b shows a SEM image of an as-fabricated top-gate graphene FET using


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EBI assistanted ALD-grown HfO2 film (with a thickness of approximately 4 nm) as the gate dielectric. The area modified by EBI (in yellow rectangle) is designed to be much larger than that of graphene in the channel (in red rectangle) to ensure complete isolation of graphene from the gate. Transfer curve of a typical graphene FET is shown in Fig. 3c, and a numerical fitting of experimental data reveals a mobility 2,392 cm2/V·s for holes and 2,481 cm2/V·s for electrons. The high and symmetric carrier mobility, as well as small Dirac point voltage (about -0.06 V), indicate that the high quality of the prinstine graphene is mainly maintained even after the EBI assistanted ALD process and other complex device fabrication processes. As a statistical comparison in Fig. 3d, results from 16 top-gate FETs are presented showing an average carrier mobility of approximately 2,500 cm2/V·s, which is slightly lower than the average carrier mobility (approximately 3,000 cm2/V·s) for pristine graphene based back-gate FETs without the fabrication of the top-gate stack. It is well known that top-gate FET fabrication always brings obvious mobility degradation in graphene FETs

34, 35

, but the light mobility degradation of our EBI-modification assistant ALD

growth method is within an acceptable level. A high quality dielectric layer must provide both high carrier mobility (low scattering) and large gate capacitance 17. In a double gated graphene FET, the top gate capacitance can be accurately calculated through measuring the efficiency ratio of the top-gate and back gate based on DC measurement curves as shown in Fig. 4a. Transfer curves (Ids-VTG) were measured under different back gate voltages (VBG) 15, 36. The top gate transfer curves present a positive shift of Dirac point voltage when the back-gate voltage varies from 40 V to -40V. Using the dual gates model shown in the inset of Fig. 4a, the gate induced charges in the graphene channel is electrostatically controlled by both the top gate and back gate electric field simultaneously. If the back-gate voltage is changed, the top-gate voltage must change to compensate the charges change induced by the back gate voltage. Therefore, the shift in the top-gate Dirac point voltage ∆VTG, Dirac is shown to be linearly dependent on the change in the back-gate voltage ∆VBG as 15



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COX / CBG = −∆VBG / ∆VTG , Dirac

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(1)

Figure 4b shows these relations between the top-gate Dirac point VTG,Dirac and back gate voltage VBG for three different graphene FETs, indicating good linear dependence according to equation (1). The slope of the VBG-VTG,Dirac curve reflects the top/back gate ratio, i.e. COX/CBG, and the efficiencies are obtained to be respectively 204, 175 and 217 for the three devices . For a SiO2 layer with a thickness of 285 nm and relative dielectric constant of 3.9, the back-gate capacitance is 0.0121 µF/cm2. The maximum top-gate capacitance is thus calculated to be 2.63µF/cm2, with an equivalent oxide thickness (EOT) of 1.3 nm. And this sets a record for the top gate relative efficiency for graphene solid state FETs 37, 38. Table 1 compares the performance of various dielectric films on graphene through different ALD growth methods. Compared with the gate dielectrics reported previously, the EBI assistanted ALD grown HfO2 film on graphene investigated in this work results in a highest carrier mobility, smallest Dirac point voltage and highest gate capacitance. We show that through this EBI modification method, an atom-thin amorphous carbon layer can be formed on graphene, which subsequently acts as a buffer layer to grow ultra-thin uniform and continuous thin HfO2 layer. Furthermore, the amorphous carbon layer possesses the same elements as carbon nanomaterials, and provides abundant dangling bonds for ALD growth. This EBI modification method can be extended to any process, which need to react with the inert nano-interface. Table 1 : Comparison between EBI modification assistance ALD grown HfO2 film and that grown by other methods on graphene

Ref Ref Ref Ref

37, 38 39 40 37

ALD

Modified

Dielectric

method

Al2O3

N2 plasma

Al2O3

Dirac point voltage

Gate capacitance

EOT

(µF/cm2)

(nm)

-5v

0.29

11.87

O2 plasma

1v

0.78

4.42

Y2O3

Y seed layer

~0.5V

1.16

2.97

HfO2

Hf seed layer

1.15V

2.5

1.38


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Ref

10

This work

HfO2

organic polymer

~-0.8v

0.18

19

HfO2

E-beam

-0.06V

2.63

1.30

CONCLUSIONS In summary, we develop a simple method to realize ALD growth of ultra-thin high-κ dielectric on graphene by using electron beam irradiation to pre-modify graphene surface. An amorphous carbon layer is formed on graphene, induced by electron beam scanning in a SEM, and then acts as seeds for ALD growth of high-κ dielectrics. Uniform HfO2 layer with equivalent oxide thickness (EOT) of 1.3 nm was grown as gate dielectric for top-gate graphene FETs, leading to an record high gate capacitance of up to 2.63μF/cm2. In addition, the fabricated top-gate graphene FETs present high statistic carrier mobility (up to 2500 cm2/V·s) and negligible gate leakage current (as low as 0.1 mA/cm2) which is sufficient for ever ultra-low power device application.

MATERIALS AND METHODS Graphene Growth and Transfer: High quality graphene was grown on Pt by chemical vapor deposition process

.

22, 23

Briefly, polycrystalline Pt foil with size of 1cm x 1cm was first heated up to 1050℃ in a 1 in. Linderberg furnace in H2 atmosphere at 300 sccm. A mixture gas of H2/CH4 (800 sccm/5 sccm) was then introduced into the system and kept for 60 min at 1050℃. After CH4 was shut down, the system was slowly cooled down to 500℃ under the protection of 200sccm H2 flow in one hour, followed with a fast cooling process by pulling the quartz tube out from the heating region. The as-grown graphene was transferred to silicon substrate with 285 nm SiO2 by a bubbling transfer process as reported in Refs [19] and [20]. After transfer, the samples were annealed in Ar/H2 (300sccm/50sccm) for 30min at atmosphere pressure and 350℃ to clean the PMMA residual.

Electron Beam Irradiation Modification



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Electron beam irradiation (EBI) modification process was performed at room temperature inside a high-vacuum SEM (FEI Quanta 600F) chamber. To reduce electron beam damage to graphene, low electron beam energy of 1.5KeV was used. We fixed the dell-time as 1 µs at each spot, resolution as 4096×3536 and magnification as 10000, with a scan area about 11um×14um. It takes about 15 s for one time to scan over an area of approximately 150µm2. The total exposure time was controlled by the repeating times of scanning process over the same area.

Device Fabrication Top-gate G-FETs were fabricated according to the process shown in Fig. 2. Graphene was patterned by electron beam lithography (EBL) followed by oxygen plasma etching. Source/drain windows were patterned by EBL on PMMA film, and contact metal of Ti/Au(5nm/40nm) was deposited by electron beam evaporation (EBE) followed by a standard lift-off process. The graphene channel was modified by an EBI modification process in the channel area. Subsequently, gate window was defined using EBL, and HfO2 film was grown by ALD at 90 ℃ by separately injecting Tetrakis (dimethylamido) hafnium(IV) (Aldrich) and H2O vapor as precursors. After ALD process, top-gate metal was formed between S/D by EBL patterning, EBE deposition of Ti/Au(20nm/40nm) and acetone lift-off process.

Supporting Information. Additional characterization of the HfO2 thickness and pristine backgate graphene device performances are available in the supporting information. AUTHOR INFORMATION Corresponding Author *E-mail: (Z.Y.Z.) [email protected]. *E-mail: (L.M.P.) [email protected].


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Author contributions Z.Z. and L.M.P. proposed and supervised the project. M.X. and C.Q. designed the experiments. M.M. performed the characterization and fabrication of the ALD-HfO2 on graphene and FET devices. M.X., Z.Z. and L.M.P. analyzed the data and co-wrote the manuscript. All authors discussed the results and commented on the manuscript.

Notes The authors declare no competing financial interest. ACKNOWLEDGMENT This work was supported by the National Key Research & Development Program (Grant Nos. 2016YFA0201901 and 2016YFA0201902), the National Science Foundation of China (Grant Nos. 61390504, 61321001 and 61427901), and the Beijing Municipal Science and Technology Commission (Grant No. D161100002616001-3).

References: 1. Novoselov, K.S.;Fal, V.I.;Colombo, L.;Gellert, P.R.;Schwab, M.G.; Kim, K. A Roadmap for Graphene.Nature 2012, 490 (7419), 192-200. 2. Franklin, A.D. Electronics: The Road to Carbon Nanotube Transistors.Nature 2013, 498 (7455), 443-444. 3. Qiu, C.G.;Zhang, Z.Y.;Xiao, M.M.;Yang, Y.J.;Zhong, D.L.; Peng, L.M. Scaling Carbon Nanotube Complementary Transistors to 5-nm Gate Lengths.Science 2017, 355 (6322), 271-276. 4. Liao, L.;Lin, Y.;Bao, M.;Cheng, R.;Bai, J.;Liu, Y.;Qu, Y.;Wang, K.L.;Huang, Y.; Duan, X. High Speed Graphene Transistors with a Self-Aligned Nanowire Gate.Nature 2010, 467 (7313), 305-308. 5. Liao, L.; Duan, X. Graphene for Radio Frequency Electronics.Mater Today 2012, 15 (7), 328-338. 6. Liao, L.;Bai, J.;Qu, Y.;Lin, Y.;Li, Y.;Huang, Y.; Duan, X. High-Κ Oxide Nanoribbons as Gate Dielectrics for High Mobility Top-Gated Graphene Transistors. Proc. Natl. Acad. Sci. USA 2010, 107 (15), 6711-6715. 7. Hollander, M.J.;LaBella, M.;Hughes, Z.R.;Zhu, M.;Trumbull, K.A.;Cavalero, R.;Snyder, D.W.;Wang, X.J.;Hwang, E.; Datta, S. Enhanced Transport and Transistor Performance with Oxide Seeded High-K Gate Dielectrics On Wafer-Scale Epitaxial Graphene.Nano Lett. 2011, 11 (9), 3601-3607.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

8. Wang, X.R.;Tabakman, S.M.; Dai, H.J. Atomic Layer Deposition of Metal Oxides On Pristine and Functionalized Graphene.J. Am. Chem. Soc. 2008, 130 (26), 8152-8153. 9. Lu, Y.R.;Bangsaruntip, S.;Wang, X.R.;Zhang, L.;Nishi, Y.; Dai, H.J. DNA Functionalization of Carbon Nanotubes for Ultrathin Atomic Layer Deposition of High κ Dielectrics for Nanotube Transistors with 60 mv/Decade Switching.J. Am. Chem. Soc. 2006, 128 (11), 3518-3519. 10. Farmer, D.B.;Chiu, H.;Lin, Y.;Jenkins, K.A.;Xia, F.N.; Avouris, P. Utilization of a Buffered Dielectric to Achieve High Field-Effect Carrier Mobility in Graphene Transistors. Nano Lett. 2009, 9 (12), 4474-4478. 11. Lim, T.;Kim, D.; Ju, S. Direct Deposition of Aluminum Oxide Gate Dielectric On Graphene Channel Using Nitrogen Plasma Treatment.Appl. Phys. Lett. 2013, 103 (1), 013107. 12. Williams, J.R.;DiCarlo, L.; Marcus, C.M. Quantum Hall Effect in a Gate-Controlled pn Junction of Graphene.Science 2007, 317 (5838), 638-641. 13. Lee, B.;Park, S.;Kim, H.;Cho, K.;Vogel, E.M.;Kim, M.J.;Wallace, R.M.; Kim, J. Conformal Al2O3 Dielectric Layer Deposited by Atomic Layer Deposition for Graphene-Based Nanoelectronics.Appl. Phys. Lett. 2008, 92 (20), 203102. 14. Zhang, L.B.;Patil, A.J.;Li, L.;Schierhorn, A.;Mann, S.;Gösele, U.; Knez, M. Chemical Infiltration During Atomic Layer Deposition: Metalation of Porphyrins as Model Substrates. Angew.Chem., Int. Ed. 2009, 48 (27), 4982-4985. 15. Xu, H.L.;Zhang, Z.Y.;Wang, Z.X.;Wang, S.;Liang, X.L.; Peng, L.M. Quantum Capacitance Limited Vertical Scaling of Graphene Field-Effect Transistor. ACS Nano 2011, 5 (3), 2340-2347. 16. Wang, Z.X.; Xu, H.L.; Zhang, Z.Y.;Wang, S.;Ding, L.;Zeng, Q.S.;Yang, L.J.;Pei, T.;Liang, X.L; Gao, M.;Peng, L.M. Growth and Performance of Yttrium Oxide as an Ideal High-Κ Gate Dielectric for Carbon-Based Electronics. Nano Lett. 2010, 10 (6), 2024-2030. 17. Xu, H.L.; Zhang, Z.Y;Xu, H.T.;Wang, Z.X.;Wang, S.; Peng, L.M. Top-Gated Graphene Field-Effect Transistors with High Normalized Transconductance and Designable Dirac Point Voltage. ACS Nano 2011, 5 (6), 5031-5037. 18. Hisamoto, D.;Lee, W.;Kedzierski, J.;Takeuchi, H.;Asano, K.;Kuo, C.;Anderson, E.;King, T.;Bokor, J.; Hu, C.M. FinFET-a Self-Aligned Double-Gate MOSFET Scalable to 20 nm. IEEE Trans. Electron Devices 2000, 47 (12), 2320-2325. 19. Wind, S.J.;Appenzeller, J.;Martel, R.;Derycke, V.; Avouris, P. Vertical Scaling of Carbon Nanotube Field-Effect Transistors Using Top Gate Electrodes.Appl. Phys. Lett. 2002, 80 (20), 3817-3819. 20. Yeo, Y.;King, T.; Hu, C.M. MOSFET Gate Leakage Modeling and Selection Guide for Alternative Gate Dielectrics Based On Leakage Considerations. IEEE Trans. Electron Devices 2003, 50 (4), 1027-1035. 21. Puurunen, R.L. Surface Chemistry of Atomic Layer Deposition: A Case Study for the Trimethylaluminum/Water Process. J. Appl. Phys. 2005, 97 (121301), 1-52. 22. Chen, B.Y.;Huang, H.X.;Ma, X.M.;Huang, L.;Zhang, Z.Y.; Peng, L.M. How Good Can CVD-Grown Monolayer Graphene be? Nanoscale 2014, 6 (24), 15255-15261.


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23. Gao, L.B.;Ren, W.C.;Xu, H.L.;Jin, L.;Wang, Z.X.;Ma, T.;Ma, L.P.;Zhang, Z.Y.;Fu, Q., Peng, L.M.; Bao X.H.;Cheng, H.M. Repeated Growth and Bubbling Transfer of Graphene with Millimetre-Size Single-Crystal Grains Using Platinum. Nat. Commun. 2012, 3, 699. 24. Ferrari, A.C.; Robertson, J. Interpretation of Raman Spectra of Disordered and Amorphous Carbon.Phys. Rev. B 2000, 61 (20), 14095. 25. Catena, A.;Agnello, S.;Cannas, M.;Gelardi, F.M.;Wehner, S.; Fischer, C.B. Evolution of the Sp2 Content and Revealed Multilayer Growth of Amorphous Hydrogenated Carbon (aC: H) Films On Selected Thermoplastic Materials. Carbon 2017, 117, 351-359. 26. Teweldebrhan, D.; Balandin, A.A. Modification of Graphene Properties Due to Electron-Beam Irradiation. Appl. Phys. Lett. 2009, 94 (1), 013101. 27. Childres, I.;Jauregui, L.A.;Foxe, M.;Tian, J.F.;Jalilian, R.;Jovanovic, I.; Chen, Y.P. Effect of Electron-Beam Irradiation On Graphene Field Effect Devices.Appl. Phys. Lett. 2010, 97 (17), 173109. 28. Choi, J.H.;Lee, J.;Moon, S.M.;Kim, Y.;Park, H.; Lee, C.Y. A Low-Energy Electron Beam Does Not Damage Single-Walled Carbon Nanotubes and Graphene. J. Phys. Chem. Lett. 2016, 7 (22), 4739-4743. 29. Smith, B.W.; Luzzi, D.E. Electron Irradiation Effects in Single Wall Carbon Nanotubes.J. Appl. Phys. 2001, 90 (7), 3509-3515. 30.

C.-H.Jan,

M.Agostinelli,

M.Buehler,

Z.-P.Chen,

S.-J.Choi,

G.Curello,

H.Deshpande,

S.Gannavaram, W.Hafez, U.Jalan, M.Kang, P.Kolar, K.Komeyli, B.Landau, A.Lake, N.Lazo, S.-H.Lee, T.Leo, J.Lin, N.Lindert, S.Ma, L.McGill, C.Meining, A.Paliwal, J.Park, K.Phoa, I.Post, N.Pradhan, M.Prince, A.Rahman, J.Rizk, L.Rockford, G.Sacks, A.Schmitz, H.Tashiro, C.Tsai, P.Vandervoorn, J.Xu, L.Yang, J.-Y.Yeh, J.Yip, K.Zhang, Y.Zhang, P.Bai A 32nm SOC Platform Technology with 2nd Generation High-K/Metal Gate Transistors Optimized for Ultra Low Power, High Performance and High Density Product Applications. IEEE Int. Electron Devices Meet.2009, 28.1.1-28.1.4; DOI: 10.1109/IEDM.2009.5424258 31. Kim, S.;Nah, J.;Jo, I.;Shahrjerdi, D.;Colombo, L.;Yao, Z.;Tutuc, E.; Banerjee, S.K. Realization of a High Mobility Dual-Gated Graphene Field-Effect Transistor with Al2 O3 Dielectric.Appl. Phys. Lett. 2009, 94 (6), 062107. 32. Glavatskikh, I.A.;Kortov, V.S.; Fitting, H. Self-Consistent Electrical Charging of Insulating Layers and Metal-Insulator-Semiconductor Structures.J. Appl. Phys. 2001, 89 (1), 440-448. 33. Woo, S.O.; Teizer, W. Effects of Electron Beam Induced Redox Processes On the Electronic Transport in Graphene Field Effect Transistors.Carbon 2015, 93, 693-701. 34. Lin, Y.M.;Jenkins, K.A.;Valdes-Garcia, A.;Small, J.P.;Farmer, D.B.; Avouris, P. Operation of Graphene Transistors at Gigahertz Frequencies.Nano Lett. 2008, 9 (1), 422-426. 35. Ponomarenko, L.A.; Yang, R.; Mohiuddin, T.M.; Katsnelson, M.I.; Novoselov, K.S.; Morozov, S.V.;Zhukov, A.A.;Schedin, F.;Hill, E.W.; Geim, A.K. Effect of a High-κ Environment On Charge Carrier Mobility in Graphene. Phys. Rev. Lett. 2009, 102 (20), 206603. 36. Meric, I.; Han, M.Y.;Young, A.F.; Ozyilmaz, B.;Kim, P.; Shepard, K.L. Current Saturation in



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Zero-Bandgap, Top-Gated Graphene Field-Effect Transistors.Nat.Nanotechnol.2008,3(11), 654-659. 37. Jeong, S.;Gu, Y.;Heo, J.;Yang, J.;Lee, C.;Lee, M.;Lee, Y.;Kim, H.;Park, S.; Hwang, S. Thickness Scaling of Atomic-Layer-Deposited HfO2 Films and their Application to Wafer-Scale Graphene Tunnelling Transistors. Sci. Rep. 2016, 6, 20907. 38. Lee, Y.;Jeon, W.;Cho, Y.;Lee, M.;Jeong, S.;Park, J.; Park, S. Mesostructured Hf XAlYO2 Thin Films as Reliable and Robust Gate Dielectrics with Tunable Dielectric Constants for High-Performance Graphene-Based Transistors. ACS Nano 2016, 10 (7), 6659-6666. 39. Nourbakhsh, A.;Adelmann, C.;Song, Y.;Lee, C.S.;Asselberghs, I.;Huyghebaert, C.;Brizzi, S.;Tallarida, M.;Schmeisser, D.;Van Elshocht, S.;Heyns, M.;Kong, J.;Palacios, T.; De Gendt, S. Graphene Oxide Monolayers as Atomically Thin Seeding Layers for Atomic Layer Deposition of Metal Oxides. Nanoscale 2015, 7 (24), 10781-10789. 40. Takahashi, N.; Nagashio, K. Buffer Layer Engineering On Graphene Via Various Oxidation Methods for Atomic Layer Deposition. Appl. Phys. Express 2016, 9 (12), 125101.


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Page 15 of 19

b)

a) Bare GR+HfO2

Pristine Graphene Graphene with EBI modification

5 (nm)

2D

G Intensity(a.u.)

0 -5

Modified GR+HfO2 5 (nm)

D 2D G

0 -5 1500

c)

2000

2500

3000

Raman shift(cm-1)

Scan time 0s

d) 105 104 103 102 101 100 10-1 10-2 10-3 10-4 10-5 10-6 10-7 -0.5

Scan time 15s

Jgate(A/cm2)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Scan time 60s

Scan time 120s

scan time 0s Scan time 90s Scan time 120s Scan time 150s Scan time 165s

0.0

0.5

Vtg(V)

Figure 1 a) AFM images showing graphene with (down) and without (up) EBI modification after ALD growth of HfO2. Bule lines shows the height profile of two surfaces. The scale bar denotes 500nm; b) Raman Spectrum obtained from graphene without (blue) and with EBI modification (red). The excitation laser wavelength is 485nm. c) SEM images showing HfO2 films on graphene gown by 35 cycles and

different scan time. The inset scale bar

denotes 200nm. d) Gate leakage currents of top gate G-FETs with 35 cycles HfO2 as the gate dielectric and different scan times.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Figure 2 Process flow showing the fabricate steps of top-gate graphene field-effect transistor through EBID assistant ALD growing HfO2 film as gate insulator.


Page 16 of 19

Page 17 of 19

a)

b)

Before EBI After EBI 60 min after EBI

100

90 min after EBI

Ids(µ µ A)

4 weeks after EBI

VDS=0.1V

10

-60

-40

-20

c)

0

20

40

60

d)

VBG(V)

Experimental Fitting

4000

40 I ds(µµA)

7 6

Hole Electron

Backgate measurement

50

Topgate measurement

30

µh=2392

5 4

-0.5

0.0 VTG(V)

0.5

1.0

µe=2481

VDS=0.1V

3

Mobility(cm2/v⋅ s)

20

10 -1.0

Rtotal(KΩ Ω)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


3000

2000

1000

2

0 -0.9

-0.6

-0.3

0.0

0.3

VTG-VDirac(V)

0.6

0.9

a bcde f gh i j k l mnop

abc de f gh i j k lmnop

Device Index

Figure 3 a). Transfer curves of back gate graphene FETs before and after EBI modification. b) SEM image showing a typical top-gate graphene FET, with a channel width /channel length/gate length of 5 µm/8 µm/5 µm. The red dash rectangle marks the graphene area, the yellow dash rectangle marks the area for EBI modification and HfO2 growth. c) Typical transfer curve of a top gate graphene FET with the same structure as in b) at bias (Vds) of 100 mV. The inset shows the as-measured transfer curve；d) Statistical results of carrier mobility for pristine graphene (with back-gate measurement before EBI modification) and graphene top gate FETs with EBI medications.



a)

b)

150 135

Device 1: COX/CBG=204

0.6


120


105

0.4 VDirac(V)

90 Ids(µ µ A)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 18 of 19

75 60 45 30

0.0

VDS=0.1 V

15

VBG from 40V to -40v,step=-10v

-1.0

-0.5

0.2

0.0

0.5

-0.2

1.0

-40

-20

0

20

40

VBG(V)

VTG(V)

Figure 4 a) Transfer curves of a top-gate G-FET under different back-gate voltages. Inset depicts a schematic view of the dual gate model. b) Relationship of Dirac point voltage and back-gate voltage for three top gate graphene FETs. Solid lines show liner fitting of experiment data.


Page 19 of 19

Table of Contents Bare GR+HfO2

5 (nm)

150 135 120

0

105

-5

Modified 5 (nm)

GR+HfO2

Ids(µ A)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


90 75 60 45

0 -5

30

VDS=0.1 V

15

VBG from 40V to -40v,step=-10v

-1.0

-0.5

0.0

0.5

1.0

VTG(V)


Atomic-Layer-Deposition Growth of an Ultrathin HfO2 Film on

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