Techniques for Production of Large Area Graphene for Electronic and Sensor Device Applications

Graphene 2D Mater. 2014; 1:47–58 Research Article Open Access Bing Li, Genhua Pan, Shakil A. Awan, and Neil Avent Techniques for Production of Large Area Graphene for Electronic and Sensor Device Applications Abstract: Here we review commonly used techniques for providing visually identifiable and nearly charge-neutral the production of large area and high quality graphene graphene layers, which make it possible to characterize to meet the requirements of industrial applications, in- the physical properties of graphene. Although graphene cluding epitaxial growth on SiC, chemical vapour deposi- has been theoretically studied for over 60 years [2] and ef- tion (CVD) on transition metals and growth from solid car- forts to make thin films of graphite by mechanical exfoli- bon source. The review makes a comparison of the growth ation date back to 1990 [4, 5], only graphite films no thin- mechanisms, quality (such as mobility and homogeneity) ner than 50 to 100 layers were produced before 2004. The and properties of the resultant graphene, limitations and significance of Manchester’s results lies in the discovery of the prospect of each production method. A particular fo- the unique electronic properties in the naturally-occurring cus of the review is on direct (transfer free) growth on di- two-dimensional material due to the unique transport electric substrate as this is potentially one of the promis- properties of massless Dirac fermions. This has led to a ing techniques for graphene production which can readily surge of research interest in this material. More extraordi- be integrated into existing semiconductor fabrication pro- nary properties of graphene have since been unearthed, cesses. such as electron mobility of 106cm2· V−1·s−1 at room tem- 2 −1 −1 perature [6] (a limit up to 40000 cm ·V ·s on SiO2 sub- DOI 10.2478/gpe-2014-0003 strate [7]), ultralow resistivity [2], anomalous quantum Received March 17, 2014; accepted October 2, 2014 hall effect [8], different electronic transport performance in armchair or zig-zag edge orientations [9], behaviour of massless Dirac fermions [10, 11], unusual band struc- ture [12, 13], high thermal stability [14], ultrahigh breaking 1 Introduction strength of 1 TPa and tensile strength of 125 GPa [15], high transparency at certain wavelengths [16, 17], high chemi- Graphene, a single-atom-thick allotrope of carbon having cal resistance [18], long spin diffusion length at room tem- 2 sp -bonded atoms in a 2-dimensional honeycomb lattice, perature [19], controllable doping level [20], etc. These ex- can be regarded as a basic building block of 3D graphite, tensive and unique properties of graphene have made the 1D carbon nanotubes and 0D fullerenes [1–3]. Graphene material to be known as the “21st century wonder mate- was first produced by the Manchester group in 2004 [1,2], rial”. It is promising for the post Moore’s era [2, 12, 21], on a Si wafer with carefully chosen thickness of SiO2, by with potential technological applications in many areas the so called scotch-tape method or mechanical exfolia- including electronics [22], photonics [23, 24], biological tion. A 300 nm thick SiO2 layer on the Si substrate elec- and chemical sensors [25, 26], energy storage [27], spin- trically isolates the graphene and weakly interacts with it, tronics [28–30] and quantum computing [31]. However, to realise its full potential for industrial scale applications, large scale production of high quality Bing Li, Genhua Pan: Wolfson Nanomaterials and Devices Labora- graphene on device compatible substrates is one of the key tory, School of Computing and Mathematics, Faculty of Science and Environment, Plymouth University, Plymouth, Devon, PL4 8AA, UK requirements. Significant progress in this respect has al- and Centre for Research in Translational Biomedicine, Plymouth ready been made since the discovery of graphene [1]. This University, Plymouth, Devon, PL4 8AA, UK paper aims to provide an up to date review of the produc- Neil Avent: Centre for Research in Translational Biomedicine, Ply- tion techniques for large area graphene films. mouth University, Plymouth, Devon, PL4 8AA, UK The techniques of large area graphene production de- Shakil A. Awan: Wolfson Nanomaterials and Devices Laboratory, veloped so far can be mainly categorized into the follow- School of Computing and Mathematics, Faculty of Science and Envi- ronment, Plymouth University, Plymouth, Devon, PL4 8AA, UK ing types [32]: epitaxial growth on SiC substrate, chemi- and Cambridge Graphene Centre, Department of Engineering, Uni- cal vapour deposition (CVD) on transition metal, physical versity of Cambridge, CB3 0FA, UK © 2014 Bing Li et al., licensee De Gruyter Open. This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivs 3.0 License. Unauthenticated Download Date | 5/23/18 11:14 PM 48 Ë B. L et al. vapour deposition (PVD) with a solid carbon source. These However, compared with graphene grown on C terminated techniques share common basic principles, which are the face, a lower mobility (102-103cm2V−1s−1) and carrier den- decomposition of inorganic or organic molecules at ele- sity (1013cm−2) can be seen as the absence of electron- vated temperatures and the formation of sp2- hybridized C- doped interface [42]. C bond on catalytic surfaces. However, each method uses The major attraction of this method is the direct specific substrate and growth conditions, such as carbon growth of graphene on insulating SiC wafers, therefore source, reaction temperature, pressure, heating and cool- transfer of graphene to another insulating substrate is ing rates, reaction duration, types and sizes of catalytic not required for device applications. This has provided a surfaces, which may lead to different requirement of post- unique platform for exploring electronic devices, such as processing for application purposes. Here, we discuss the field effect transistors and integrated electronic circuits, characteristics of each method together with their advan- which has attracted major interest in the field [43]. For ex- tages and disadvantages for device applications. ample, graphene transistors operating at 100 GHz frequen- cies [44] and graphene integrated circuits operating at fre- quencies up to 10 GHz [45] have recently been developed 2 Epitaxial growth from single by IBM. However, the epitaxial technique has several limita- crystal SiC substrates tions in meeting the industrial requirements for electronic applications. In particular, the graphene grown on the sin- Berger and his co-workers reported in 2004 [21], the same gle crystal SiC wafers is not atomically flat as those on Si year as the discovery of exfoliated graphene [1], the epitax- wafers, but with a terraced morphology [12], as typically ial growth of ultrathin graphite films by thermal decom- shown in Fig. 1 [40]. The high cost of the SiC crystal start- position of 6H-SiC(0001) single crystals in an ultrahigh ing material also renders it impractical for large-scale com- vacuum (UHV), which was perhaps the first technique re- mercial applications. The very high growth temperature in ported for large area graphene production, although the ultra-high vacuum is another limitation. solid-state graphitization mechanisms of silicon carbide had been studied well before 2004 [33, 34]. The production of monolayer epitaxial graphene was subsequently re- 3 Chemical Vapour Deposition ported by the same group in 2006 [12]. When a single crystal SiC substrate is heated up to a temperature in excess of One of the major breakthroughs in the production of 1200 °C in an UHV chamber, the Si atoms on the surface are large area graphene, following the epitaxial method, is sublimated due to the lower vapor pressure [34–36], leav- the growth of graphene by CVD method [46–48] using ing behind C atoms on the SiC crystal surface. Because of short chain hydrocarbon gases, such as methane and ethy- the very small mismatch of the SiC(0001) crystal and the lene [49–53], on a catalytic surface of transition metals, graphene honeycomb lattices, the carbon atoms are able to such as Ni [17, 54, 55], Ru [56–58], Ir [59], Au [60], Cu [46], reconstruct into a graphene sheet on top of the SiC (0001) Pt [61], Rh [62, 63], Pd [64, 65] and Fe [66]. Short chain hy- crystal surface [21, 37]. drocarbon gases have long been used in carbon nanotube The epitaxial growth of graphene on single crystal SiC growth [67, 68]. A limited number of early attempts before is not self-limiting. The number of layers, quality and prop- 2004 can also be found on the growth of very thin graphite erties of the graphene depends on whether the graphene layers or even monolayer graphite by CVD, for example, on grows on the Si or C terminated face, and also on the Pt(111) by Land et al. [69], and on TiC(111) by Nagashima et annealing temperatures [38, 39] and the vacuum condi- al. [70], however, no attempts have been made in the char- tions [40]. On the C terminated face, graphene tends to acterization of the electron transport properties of these grow into more layers, usually more than 10 layers. The films. first few layers are highly electron-doped with random In the CVD growth process, a polycrystalline metal orientation while the subsequent layers are not as much sheet [71, 72], or metal film deposited on a substrate [73, doped as the first few layers [41]. The electronic proper- 74], acting as a catalytic surface, is usually pre-annealed ties of the graphene layers are affected by these electronic (800-1000°C) in vacuum to obtain larger crystalline grains. charges and show a mobility of 104-105cm2V−1s−1 with Short chain hydrocarbon molecules are then introduced to the corresponding carrier density of 1013cm−2. In contrast, the chamber, where they are adsorbed on the metal sur- growth of graphene on the Si face is more controllable, face, decompose into carbon atoms and form graphene resulting in fewer layers with improved properties [41].

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