Edge Engineered Graphene Nanoribbons as Nanoscale Interconnect: DFT Analysis

Density functional theory (DFT) with non-equilibrium Green's function (NEGF) formalism and HSPICE simulator have been used to analyse the effect of elemental oxygen atom passivation on the structural, electronic and transport properties of Graphene Nanoribbons (GNRs). The analysis of delay, power dissipation, crosstalk effect, stability and frequency analysis has also been performed to understand its interconnect application. The present study includes all the possible morphologies of zigzag and armchair edge states of GNRs with oxygen and hydrogen passivation. The structural stability of GNRs, analysed in terms of binding energy $(E_{binding})$ observed that the Zigzag graphene nanoribbon (ZGNR) with both edge oxygen passivated, is the most stable configuration, where stability of the configuration increases with Oxygen concentration. Further, frotextm the bandstructure and density-of-states calculations, it has been observed that considered 6 atom wide and hydrogen passivated Armchair GNR (AGNR) is semiconducting in nature, whereas, with same width hydrogen passivated ZGNR is metallic. On the other hand, passivation of AGNR with increasing concentration of oxygen form them to metallic in nature. Based on the enhanced metallicity and increment in fermi velocity due to passivation of GNRs with oxygen, these structures may be a potential candidate for interconnects. Their computed electron transport properties, dynamical parameters, delay, power delay product and crosstalk induced delay confirms that the zigzag GNR with both the edges passivated with oxygen (O-ZGNR-O) can be considered as best contender for interconnect application due to its remarkable electrical and thermal transport in comparison to other GNR's. The O-ZGNR-O shows lowest value of kinetic inductance and quantum capacitance of. 01032H/m and 2.21 nF/m respectively with higher stability and higher immunity to crosstalk effect in comparison to other proposed GNRs, which is required for nanoscale interconnects. The relative stability of GNRs have been analyzed in terms of nyquist plot with different interconnect lengths. The results suggest that O-ZGNR-O have lowest delay and power dissipation with higher stability, hence defends its application for interconnect application.

I. Introduction

Since last one decade, we have breached all conventional laws for the scaling of devices and reached to an age of nanoscale devices [1], [2]. At nanoscale, the interconnects face various challenges, that affects their performance like enhanced delay and parasitic effects [3]. Due to reliability issues with aluminum initially used, Aluminum (Al) had been replaced by Copper (Cu). However, the Cu also has few drawbacks at the nanoscale, like the resistance of copper interconnects increases expeditiously due to its small mean free path [4]–[6]. Mean free path of electrons is due to the combined effects of scattering (grain boundary, side wall scattering of electrons) and electro migration. Due to these challenges with Cu interconnects at Nanoscale, the conventional Cu material has been attempted to get replaced by the nanostructures of carbon. Resistance, inductance, capacitance and delay of the device have become more and more pronounced issues for choosing the best interconnect materials. Graphene, an allotrope of carbon is a two dimensional (2D) material, which has 0.34 nm atomic layer of carbon with hexagonal honeycomb structure. This 2D monolayer has various unique properties [7] like high current density with low resistivity, large mean free path, higher superconductivity [10], making it a better and reliable candidate for the next-generation interconnects. In the last few years, the research on one dimensional materials has made remarkable progress, reason being the bulk silicon (Si) technology is approaching its physical limit and inturn challenges like unwanted tunneling [11], leakage currents, and scattering at nanoscale, hence graphene can be considered as the promising candidate to replace Si in future nanoelectronic devices. Graphene nanoribbons (GNRs) are greatly studied, both experimentally and theoretically for possible nanoelectronic device applications [12]–[14]. It can be used as semiconductors or conductors depending on the edge configurations [15], [16], semiconducting graphene can be used in transistor channels while its metallic counterparts can be used in interconnect applications. For the practical implementation, the graphene nanoribbons (GNRs) could be the most suitable for interconnect. Although, the geometric structure changes the property of GNR slightly, compared to the ideal behaviour of graphene [3]. Due to this, graphene nanoribbons have emerged as an interesting material for interconnects application. The most common form of graphene nanoribbons are Zigzag and Armchair, where Zigzag nanoribbons are always metallic and Armchair nanoribbons may be semiconducting or metallic depending on the width.