Size-Dependent Grain Boundary Scattering in Topological Semimetals

We assess the viability of topological semimetals for application in advanced interconnect technology, where conductor size is on the order of a few nanometers and grain boundaries are expected to be prevalent. We investigate the electron transport properties and grain boundary scattering in thin films of the topological semimetals CoSi and CoGe using first-principles calculations combined with the Non-Equilibrium Green's Function (NEGF) technique. Unlike conventional interconnect metals like Cu and Al, we find that CoSi and CoGe conduct primarily through topologically-protected surface states in thin film structures even in the presence of grain boundaries. The area-normalized resistance decreases with decreasing film thickness for CoSi and CoGe thin films both with and without grain boundaries; a trend opposite to that of the conventional metals Cu and Al. The surface-dominated transport mechanisms in thin films of topological semimetals with grain boundaries demonstrates a fundamentally new paradigm of the classical resistivity size-effect, and suggests that these materials may be promising candidates for applications as nano-interconnects where high electrical resistivity acts as a major bottleneck limiting semiconductor device performance.Comment: 18 pages, 9 figures. To be published in Physical Review Applie

A first-principles analysis of ballistic conductance, grain boundary scattering and vertical resistance in aluminum interconnects

We present an ab initio evaluation of electron scattering mechanisms in Al interconnects from a back-end-of-line (BEOL) perspective. We consider the ballistic conductance as a function of nanowire size, as well as the impact of surface oxidation on electron transport. We also consider several representative twin grain boundaries and calculate the specific resistivity and reflection coefficients for each case. Lastly, we calculate the vertical resistance across the Al/Ta(N)/Al and Cu/Ta(N)/Cu interfaces, which are representative of typical vertical interconnect structures with diffusion barriers. Despite a high ballistic conductance, the calculated specific resistivities at grain boundaries are 70-100% higher in Al than in Cu, and the vertical resistance across Ta(N) diffusion barriers are 60-100% larger for Al than for Cu. These results suggest that in addition to the well-known electromigration limitations in Al interconnects, electron scattering represents a major problem in achieving low interconnect line resistance at fine dimensions

Supercapacitors based on patronite-reduced graphene oxide hybrids: experimental and theoretical insights

Here we report the hydrothermal synthesis and detailed study on supercapacitor applications of a patronite hybrid, VS4/reduced graphene oxide, which showed an enhanced specific capacitance of similar to 877 F g(-1) at a current density of 0.5 A g(-1). In comparison to bare vanadium sulfide and reduced graphene oxide, the hybrid showed similar to 6 times and similar to 5 times higher value of specific capacitance, respectively. The obtained energy density (117 W h kg(-1)) and power density (20.65 kW kg(-1)) are comparable to those of other reported transition metal sulfides and their graphene hybrids. Theoretical calculations using density functional theory confirm an enhanced quantum capacitance of VS4/graphene composite systems, owing primarily to the shifting of the graphene Dirac cone relative to the band gap of VS4. The results infer that the hybrid has the potential to be used as a high performance supercapacitor electrode3371887418881Department of Science & Technology (India); Science Engineering Research Board (SERB), India; DST-CNPq/India-Brazil bilateral Cooperation; Interconnect Focus Center (MARCO program); State of New York ; National Science Foundation (NSF); Indo-US Science and Technology Forum (IUSSTF) through a joint INDO-US centre grant; Ministry of Human Resources Development (MHRD), India through a center of excellence gran

Surface-dominated conductance scaling in Weyl semimetal NbAs

Abstract Protected surface states arising from non-trivial bandstructure topology in semimetals can potentially enable advanced device functionalities in compute, memory, interconnect, sensing, and communication. This necessitates a fundamental understanding of surface-state transport in nanoscale topological semimetals. Here, we investigate quantum transport in a prototypical topological semimetal NbAs to evaluate the potential of this class of materials for beyond-Cu interconnects in highly-scaled integrated circuits. Using density functional theory (DFT) coupled with non-equilibrium Green’s function (NEGF) calculations, we show that the resistance-area R A product in NbAs films decreases with decreasing thickness at the nanometer scale, in contrast to a nearly constant R A product in ideal Cu films. This anomalous scaling originates from the disproportionately large number of surface conduction states which dominate the ballistic conductance by up to 70% in NbAs thin films. We also show that this favorable R A scaling persists even in the presence of surface defects, in contrast to R A sharply increasing with reducing thickness for films of conventional metals, such as Cu, in the presence of surface defects. These results underscore the potential of topological semimetals as future back-end-of-line (BEOL) interconnect metals

Unconventional resistivity scaling in topological semimetal CoSi

Abstract Nontrivial band topologies in semimetals lead to robust surface states that can contribute dominantly to the total conduction. This may result in reduced resistivity with decreasing feature size contrary to conventional metals, which may highly impact the semiconductor industry. Here we study the resistivity scaling of a representative topological semimetal CoSi using realistic band structures and Green’s function methods. We show that there exists a critical thickness d c dividing different scaling trends. Above d c , when the defect density is low such that surface conduction dominates, resistivity reduces with decreasing thickness; when the defect density is high such that bulk conduction dominates, resistivity increases as in conventional metals. Below d c where bulk states are depopulated, the persistent Fermi-arc remnant states give rise to decreasing resistivity down to the ultrathin limit, unlike topological insulators. The observed CoSi scaling can apply to broad classes of topological semimetals, providing guidelines for materials screening in back-end-of-line interconnect applications