Breakdown current density of graphene nanoribbons

Abstract

Graphene nanoribbons (GNRs) with widths down to 16 nm have been characterized for their currentcarrying capacity. It is found that GNRs exhibit an impressive breakdown current density, on the order of 10 8 A/cm 2 . The breakdown current density is found to have a reciprocal relationship to GNR resistivity and the data fit points to Joule heating as the likely mechanism of breakdown. The superior current-carrying capacity of GNRs will be valuable for their application in on-chip electrical interconnects. The thermal conductivity of sub-20 nm graphene ribbons is found to be more than 1000 W/m-K.Keywords: Graphene, Breakdown current density, Nano ribbons, Maximum current * raghu@gatech.edu, Ph: 404 385 6463 2 Graphene is a promising electronic material because of many interesting properties like ballistic transport 1 , high intrinsic mobility 2 , and width-dependent bandgap 3 . Graphene, in its 2D form, has been shown to have a high thermal conductivity 4 of around 5000 W/m-K pointing to its potential use as an on-chip heat spreader.Graphene nano ribbons (GNRs) have been predicted to be superior to Cu in terms of resistance per unit length 5 for use as on-chip interconnects. A high current-carrying capacity is critical for interconnect applications and reliability. There have been a number of studies on carbon nanotube (CNT) breakdown current density, and the current-carrying capacity of single-walled CNTs 6 is found to be on the order of 10 8 A/cm 2 ; in carbon nanofibers, the breakdown current density (J BR ) has been measured 7 to be around 5x10 6 A/cm 2 . Electrical breakdown has been used to burn away successive shells in a multi-wall CNT 8,9 . More recently, electrical breakdown has been used to obtain semiconducting CNTs from a mixture of CNTs since metallic ones burn away at a lower breakdown voltage 10 . Theoretical projections suggest that J BR of graphene should be on the same order as for CNTs. However, little experimental evidence exists on the electrical breakdown of either 2D graphene or 1D GNRs. In this work, it is experimentally shown that GNRs demonstrate an impressive J BR . A simple relation between J BR and nanowire resistivity is seen to emerge from the experimental data.Few-layer graphene (1-5 layers) is used as the starting material (see supporting material 11 ).Each device consists of parallel ribbons fabricated between sets of electrodes, Fig. 1. The ribbon width between a pair of electrodes is designed to be the same for all the parallel ribbons. The range of widths studied in this work is 16nm<W<52nm, while the range of length is 0.2µm<L<1.0µm. Twenty one devices have been studied in this work, with each device yielding 5-10 GNRs (depending on the overlap of patterned channels to few-layer graphene) between the middle electrode pair. The outer electrode pair is used to test for contact resistance (in a four-point probe setup). A semiconductor analyzer is used to apply a voltage ramp (at the rate of 50 mV/s) between the middle electrodes. Due to increasing current density in the GNRs, the...

Graphene-on-Diamond Devices with Increased Current-Carrying Capacity: Carbon sp2-on-sp3 Technology

“…For graphene-on-UNCD, we obtained J BR ≈5×10 8 A/cm 2 as the highest value, while the majority of devices broke at J BR ≈2×10 8 A/cm 2 . The reference graphene-on-SiO 2 /Si had J BR ≈10 8 A/cm 2 , which is consistent with literature [7][8][9]. The Graphene-on-Diamond: Carbon sp 2 -on-sp 3 Technology, UCR and ANL, Nano Letters (2012) 11 comparison with our own reference devices is more meaningful because they had similar graphene channel length, width, aspect ratio, quality and location of the metal pads, which serve as additional heat sinks.…”

“…We note here that FLG ribbons studied in Ref. [7] had the width of 22 nm and length of 0.75 m. For this reason, the close proximity of the source and drain metal contacts could have influenced the overall value of the breakdown current density.…”

“…All our measurements have been performed under ambient conditions where the thermal breakdown can be facilitated by oxidation. The oxidation temperature is likely in the range 600 -800 o C [7,36]. One should Graphene-on-Diamond: Carbon sp 2 -on-sp 3 Technology, UCR and ANL, Nano Letters (2012) 14 expect that the JBR for the high quality graphene-on-diamond in vacuum will be substantially higher.…”

Clar’s Theory, π-Electron Distribution, and Geometry of Graphene Nanoribbons

“…Since its first characterization in 2004, 1 graphene has developed into a major research topic of its own and from the beginning, its unique electron transport properties [2][3][4][5][6][7] (For a review, see Ref. 8 ) have propelled the hope for application in a post-silicon generation of electronic devices.…”

Contact resistivity and current flow path at metal/graphene contact

“…An increase in the on/off current ratio (I on /I off ) is one of the critical issues to realize the graphene FETs. Although the contact properties are important in terms of an increase in I on , only a small number of experiments [1][2][3][4][5][6] have addressed this matter compared to the bandgap engineering for a decrease in I off . 7,8 In fact, an ohmic contact is obtained without any difficulty due to the lack of a bandgap, but it is concerned that a very small density of states (DOS) for graphene might suppress the current injection from the metal to graphene.…”