Intrinsic graphene/metal contact

Nagashio, Kosuke; Ifuku, Ryota; Moriyama, Takaaki; Nishimura, Tomonori; Toriumi, Akira

doi:10.1109/iedm.2012.6478975

Cited by 11 publications

(9 citation statements)

References 11 publications

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“…The large contact resistance with graphene arises from the lack of surface bonding sites, that causes lack of chemical bonding and strong orbital hybridization [89,127,[144][145][146][147]. Several different approaches have been exploited to reduce the contact resistance, such as work function engineering [148], cleaning of source/drain contact areas before the metallization [111,140,143], double contacts geometry [142,149], patterning of contact region [127], carbide formation [150], graphitic contact formation [151].…”

Section: Improving Contact Resistancementioning

confidence: 99%

The role of contact resistance in graphene field-effect devices

Giubileo¹,

Bartolomeo

2017

Progress in Surface Science

217

144

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The extremely high carrier mobility and the unique band structure, make graphene very useful for field-effect transistor applications. According to several works, the primary limitation to graphene based transistor performance is not related to the material quality, but to extrinsic factors that affect the electronic transport properties. One of the most important parasitic element is the contact resistance appearing between graphene and the metal electrodes functioning as the source and the drain. Ohmic contacts to graphene, with low contact resistances, are necessary for injection and extraction of majority charge carriers to prevent transistor parameter fluctuations caused by variations of the contact resistance. The International Technology Roadmap for Semiconductors, toward integration and down-scaling of graphene electronic devices, identifies as a challenge the development of a CMOS compatible process that enables reproducible formation of low contact resistance. However, the contact resistance is still not well understood despite it is a crucial barrier towards further improvements. In this paper, we review the experimental and theoretical activity that in the last decade has been focusing on the reduction of the contact resistance in graphene transistors.We will summarize the specific properties of graphene-metal contacts with particular attention to the nature of metals, impact of fabrication process, Fermi level pinning, interface modifications induced through surface processes, charge transport mechanism, and edge contact formation.

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Section: Improving Contact Resistancementioning

confidence: 99%

The role of contact resistance in graphene field-effect devices

Giubileo¹,

Bartolomeo

2017

Progress in Surface Science

217

144

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show abstract

“…Previous works to understand the graphene-metal interaction have focused on achieving low contact resistance. Broadly speaking, these efforts have involved: (1) obtaining a clean graphene-metal interface [3,[9][10][11][12], (2) contacting graphene through reactive edge-states or defects to form metal-carbides (also called end-contacted) [13][14][15][16][17], and (3) work function engineering [18][19][20][21][22]. However, all of these efforts involved graphene that was contaminated and/or modified before metal deposition by lithography resists and/or plasma exposure, or end-contacted which impede systematic investigations of various parameters on achieving lower contact resistance.…”

Section: Introductionmentioning

confidence: 99%

In search of quantum-limited contact resistance: understanding the intrinsic and extrinsic effects on the graphene–metal interface

et al. 2016

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Owing to its two-dimensional structure, graphene is extremely sensitive to surface contamination. Conventional processing techniques inevitably modify graphene's intrinsic properties by introducing adsorbents and/or defects which limit device performance and understanding the intrinsic properties of graphene. Here we demonstrate femtosecond laser direct patterning of graphene microstructures, without the aid of resists or other chemicals, that enables us to study both intrinsic and extrinsic effects on the graphene-metal interface. The pulsed femtosecond laser was configured to ablate epitaxial graphene (EG) on a sub-micrometer scale and form a precisely defined region without damaging the surrounding material or substrate. The ablated area was sufficient to electrically isolate transfer length measurement structures and Hall devices for subsequent transport measurements. Using pristine and systematically contaminated surfaces, we found that Ni does not form bonds to EG synthesized on SiC in contrast to the well-known C-Ni bond formation for graphene synthesized on metals; known as end-contacting. Without end-contacting, the contact resistance (R C ) of Ni to pristine and resistcontaminated EG are one and two orders of magnitude larger, respectively, than the intrinsic quantum limited contact resistance. The range of reported R C values is explained using carrier transmission probability, as exemplified by the Landauer-Büttiker model, which is dependent on the presence or absence of end-contacts and dopant/work-function mediated conduction. The model predicts the need for both end-contacts and a clean graphene-metal interface as necessary conditions to approach quantum limited contact resistance.

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“…Recently, a number of approaches have been explored to address the issue of poor contacts such as gentle plasma treatment, , ultraviolet/ozone (UVO) treatment, , use of a sacrificial layer, and annealing treatment. ,, The underlying principle of these approaches is to minimize resist residues that are left over at the source/drain contact regions of graphene devices by the lithography process. Out of these approaches, annealing treatment following a series of fabrication processes is the most common practice that has been adopted in many laboratories. − Although decomposition of resist residues takes place at temperatures higher than 200 °C, , the question is whether the resist residues sandwiched between the metal and graphene at the contacts can be removed by annealing because they had already been covered by thick metal film. Indeed, Chan et al observed no significant changes to the contact resistance of their nickel-contacted graphene devices following annealing at 300 °C for 3 h .…”

mentioning

confidence: 99%

“…Indeed, Chan et al observed no significant changes to the contact resistance of their nickel-contacted graphene devices following annealing at 300 °C for 3 h. 10 On the other hand, Nagashio et al found that the contact resistance of their resistfree nickel-contacted graphene devices that had been metallized by evaporation through a shadow mask is similar to that of resist-processed devices upon annealing. 8 More interestingly, to facilitate formation of covalent bonding between metal and graphene edges, annealing treatment plays an indispensable role where the graphene edges are defective 14 but is redundant for defect-free zigzag graphene edges. 15 All of these inconsistent observations give rise to the question of what annealing does to metal−graphene contacts to result in contact enhancement in most cases but insignificant changes under other circumstances.…”

mentioning

confidence: 99%

What Does Annealing Do to Metal–Graphene Contacts?

2014

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Annealing is a postprocessing treatment commonly used to improve metal–graphene contacts with the assumption that resist residues sandwiched at the metal–graphene contacts are removed during annealing. Here, we examine this assumption by undertaking a systematic study to understand mechanisms that lead to the contact enhancement brought about by annealing. Using a soft shadow-mask, we fabricated residue-free metal–graphene contacts with the same dimensions as lithographically defined metal–graphene contacts on the same graphene flake. Both cases show comparable contact enhancement for nickel–graphene contacts after annealing treatment signifying that removal of resist residues is not the main factor for contact enhancement. It is found instead that carbon dissolves from graphene into the metal at chemisorbed Ni– and Co–graphene interfaces and leads to many end-contacts being formed between the metal and the dangling carbon bonds in the graphene, which contributes to much smaller contact resistance.

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Intrinsic graphene/metal contact

Cited by 11 publications

References 11 publications

The role of contact resistance in graphene field-effect devices

The role of contact resistance in graphene field-effect devices

In search of quantum-limited contact resistance: understanding the intrinsic and extrinsic effects on the graphene–metal interface

What Does Annealing Do to Metal–Graphene Contacts?

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