A physics-based investigation of Pt-salt doped carbon nanotubes for local interconnects

Ramos

et al. 2019

In this paper, we investigate by combining electrical measurements with an atomistic-to-circuit modeling approach, the conductance of doped stand-alone multi-wall carbon nanotubes (MWCNTs) as a viable candidate for the next-generation of back-end-of-line (BEOL) interconnects. Ab-initio simulations predict a doping-related shift of the Fermi level, which reduces shell chirality variability and improves electrical resistivity up to 90% by converting semiconducting shells to metallic. Electrical measurements of Pt-salt doped CNTs provide up to 50% of resistance reduction, which is a milestone result for future CNT interconnect technology. Moreover, we find that defects and contacts introduce additional resistance, which limits the efficiency of doping and are the primary cause for the mismatch between theoretical predictions and experimental measurements on doped CNTs. Index Terms-Carbon nanotube, defective CNTs, doped CNTs, local on-chip interconnects, individual CNT growth, doping process of CNT, CNT contact resistance.

Section: A Doping Of Mwcntmentioning

confidence: 99%

Investigation of Pt-Salt-Doped-Standalone- Multiwall Carbon Nanotubes for On-Chip Interconnect Applications

Ramos

et al. 2019

“…For MWCNT, both CNT diameter and number of shells can fluctuate during the fabrication process. Typically, the diameter variation of fabricated CNT shows a Gaussian or normal (N ) distribution [19], [20].…”

Section: A Diameter Variationsmentioning

confidence: 99%

“…1. However, preliminary experimental results suggest that if each catalyst nanoparticle is confined in a nanoscale via hole [19], the relative diameter variation of individually grown MWCNT can be reduced below 10%. It is believed that this variation, which includes both catalyst size variation and intrinsic CNT growth variation, can be further reduced by improving the nanoscale via hole fabrication process.…”

Section: A Diameter Variationsmentioning

confidence: 99%

Variability Study of MWCNT Local Interconnects Considering Defects and Contact Resistances--Part I: Pristine MWCNT

Lee

et al. 2018

In this paper, an enhanced compact model of multiwalled carbon nanotube (MWCNT) interconnects while considering defects and contact resistance is proposed. Based on the atomistic-level simulations, we have found that defect densities impact MWCNT resistance and ultimately their electrical performance. Furthermore, we have computed by atomisticlevel simulations the end-contact resistance between single-wall carbon nanotube (SWCNT) and Palladium (Pd) electrode to mimic the Pd-CNT end-contact resistance of each CNT shell in MWCNT. We have developed an advanced shell-by-shell model to include various parameters such as shell diameter, shell chirality, defects on each shell, and connectivity of each shell to endcontacts. We run Monte Carlo simulations to perform variability studies on each of these parameters to understand the electrical performance variation on MWCNT interconnects. We present simulation results to convey the critical impact of variations. The impact of doping on MWCNT variability in the form of Fermi level shift will be addressed in Part II of this paper.

“…As described in [20], we developed a CNT integration process to grow individual MWCNTs at predefined locations on a silicon wafer by hot filament assisted CVD, and to individually contact them with Palladium (Pd) electrodes for electrical characterization. External doping of the MWCNT by PtCl 4 salt was then developed.…”

Section: Comparisons With Experimental Datamentioning

confidence: 99%

“…Doping is capable of changing semiconducting CNTs into metallic CNTs concerning their electrical performance, and thus it is possible to reduce chirality variation and overall MWCNT resistance variation. In [20], we showed by atomistic-level simulation and experimental results how doping alters CNT chirality. However, there is still a need for further investigations to understand the impact of doping in the presence of various sources of variations such as defects, diameter, chirality, and connectivity.…”

Section: Introductionmentioning

confidence: 99%

Variability Study of MWCNT Local Interconnects Considering Defects and Contact Resistances--Part II: Impact of Charge Transfer Doping

Lee

et al. 2018

In this paper, the impact of charge transfer doping on the variability of MWCNT local interconnects is studied by experiments and simulations. We calculate the number of conducting channels of both metallic and semiconducting CNTs as a function of Fermi level shift due to doping based on the calculation of transmission coefficients. By using the MWCNT compact model proposed in Part I of this paper, we study the charge transfer doping of MWCNTs employing Fermi level shift to reduce the performance variability due to changes in diameter, chirality, defects and contact resistance. Simulation results show that charge transfer doping can significantly improve MWCNT interconnect performance and variability by increasing the number of conducting channels of shells and degenerating semiconducting shells to metallic shells. As a case study on a MWCNT of 11 nm outer diameter, when the Fermi level shifts to 0.1 eV, up to ∼80% of performance and standard deviation improvements are observed. Furthermore, a good match between experimental data and simulation results is observed, demonstrating the effectiveness of doping, the validity of the MWCNT compact model and proposed simulation methodology. Index Terms-multi-walled carbon nanotubes, charge transfer doping, defects, Fermi level, variability, Monte Carlo simulation.