SWCNT Bundle Research Articles

Performance Analysis of CNT Bundle Interconnects in Various Low-k Dielectric Media

The capacitance of the interconnect, which contributes to RC delay, power, and crosstalk, is increasingly limiting the performance of ULSI chips as IC technology advances. Different dielectric materials are employed as electrical shielding between interconnects (also called as inter-wire dielectrics) to minimise the coupling capacitance of closely spaced interconnects, and they are compared in terms of their performance. For SWCNT and MWCNT interconnects at various global interconnect lengths for 20 nm and 14 nm technology nodes, performance parameters such as crosstalk delay, power dissipation, power crosstalk delay product (PCDP) and crosstalk noise are calculated and compared. It is observed that, upon using different dielectric materials in CNT bundle interconnect, MWCNT bundle interconnects is performing better compared to SWCNT bundle interconnects at 20 nm and 14 nm technology nodes for all global interconnect lengths.

Novel Circuit Model of Multi-walled CNT Bundle Interconnects Using Multi-valued Ternary Logic

This research paper presents a novel circuit modeling and analysis of ternary logic for MWCNT bundle interconnects with active shielding under the influence of temperature variations. The far end crosstalk-induced noise and propagation delay of MWCNT bundle interconnects has been analyzed with and without the effect of shielding. A standard ternary inverter (STI) driver model is used to obtain the ternary logic at output. The temperature-dependent analysis is also carried out at different temperatures such as 300, 400 and 500 K. The temperature-dependent comparative analysis for MWCNT bundle, SWCNT bundle and copper interconnects with and without shielding is also performed. It has been observed that MWCNT bundle with active shielding outperforms the SWCNT and Cu by 75.7% and 84.4%, respectively. Similarly, the power dissipation is substantially reduced in the case of MWCNT bundle with respect to the Cu and SWCNT interconnects. It is also reported that the noise margin is marginally stable in ternary interconnects under the influence of temperature variation.

High‐speed sub‐threshold operation of carbon nanotube interconnects

Sub-threshold voltage operated circuits are the future for ultra-low-power applications. These circuits are inherently slow due to the very small sub-threshold currents. Here, the authors propose two approaches for improving the speed of SWCNT bundle interconnects driven by CNTFET-based circuits under sub-threshold conditions. First, the authors modulate the channel length of the CNTFETs that are used in the driver circuits to increase sub-threshold output current. The output current is maximum when the channel length is optimised to 15 nm. Second, the authors design driver circuits made of CNTFET-based inverters and transmission gates for SWCNT bundle interconnects at sub-threshold voltages. The authors consider five different configurations of the driver and load circuits. SPICE simulations show that transmission gates play a vital role in driver circuits by reducing the propagation delay and increasing the switching speed at high frequencies. Finally, the authors perform temperature-dependent analysis of the best cases from the proposed circuits and show that the propagation delay and power dissipated by them increases drastically at increased temperatures up to 500 K.

Modelling and analysis of crosstalk induced noise effects in bundle SWCNT interconnects and its impact on signal stability

In order to analyse crosstalk delay and stability in single wall carbon nanotube bundle (SWCNT) interconnects, the time and frequency domain response are investigated in this paper. Based on the transmission line model and by using matrix formulation, we perform the Nyquist stability analysis to survey the dependence of the degree of relative stability for coupled SWCNT bundle interconnects. We present an exact transfer function formula for a SWCNT bundle and two coupled SWCNT bundle interconnects. The proposed model can be extended to coupled n bundled SWCNT interconnects. In order to demonstrate the crosstalk effects, we seek to compare the coupled SWCNT bundle interconnects with the SWCNT bundle interconnect. The results show that due to the capacitive and mutual inductive couplings between two SWCNT bundles, the stability of near-end output increases and the created undesirable voltage on the far-end output may reduce the stability and degrade logic. Also, it is observed that stability and switching delay of near-end output increases with increasing the interconnect length and diameter. Furthermore, maximum overshoot and switching delay of far-end output increases with length and diameter of interconnect. Also, as the parasitic coupling capacitance increases and the mutual inductance decreases, stability of near-end output increases whereas the stability of the far-end output decreases. Finally, compared to Advanced Design System results, the model exhibits an excellent accuracy.

Humidity-enhanced sub-ppm sensitivity to ammonia of covalently functionalized single-wall carbon nanotube bundle layers

A low-cost method for carbon nanotubes (CNTs) network production from solutions on flexible polyethylene naphthalate substrates has been adopted to prepare high quality and well characterized SWCNT bundle layers to be used as the active layer in chemiresistor gas sensors. Two types of SWCNTs have been tested: pristine SWCNTs, deposited from a surfactant solution, and covalently functionalized SWCNTs, deposited from a dimethyl-acetamide solution. The humidity effects on the sensitivity of the SWCNTs network to NH3 have been investigated. The results show that relative humidity favors the response to NH3, confirming recent theoretical predictions. The COOH-functionalized sample displays the largest response owing to both its hydrophilic nature, favoring the interaction with H2O molecules, and its largest surface area. Compared to data available in the literature, the present sensors display a remarkable sensitivity well below the ppm range, which makes them quite promising for environmental and medical applications, where NH3 concentrations (mostly of the order of tens of ppb) have to be detected.

Thermally aware performance analysis of single-walled carbon nanotube bundle as VLSI interconnects

A comparative performance analysis in terms of delay, power dissipation, power delay product (PDP), and crosstalk noise between SWCNT bundle interconnects with resistance estimated using conventionally (temperature independent model), and thermally aware model is investigated. The results are also compared with those of currently used copper interconnects at 22 nm technology node. It is observed that, with rise in temperature from 300 to 500 K, SWCNT bundles have a lower delay than that of copper interconnect at different lengths from 100 to $$1000\,\upmu \hbox {m}$$1000μm whereas reverse is true for power dissipation. The SPICE simulation results further reveal that for temperature variations ranging from 300 to 500 K, compared to conventional metal (copper) conductors, crosstalk noise voltage levels (positive peaks) in capacitively coupled SWCNT bundle, at the far end of victim line, are significantly low. Moreover, a relative average improvement in delay, power, and PDP using a thermally aware model in comparison with a temperature independent model is about 22.44, 7.59 and 31.96 %, respectively, with length variations from 100 to $$1000\,\upmu \hbox {m}$$1000μm, whereas for varied tube diameter is about 16.6, 5.6 and 19.72 %, respectively. The average relative improvement in the time duration reduction of victim output, for varied tube diameters, is about 21.7 % by using a thermally-aware model instead of a temperature-independent model of an SWCNT bundle resistance.

Adsorption of F127 onto single-walled carbon nanotubes characterized using small-angle neutron scattering.

Aqueous single-walled carbon nanotube dispersions are often made using polymers from the pluronic family of amphiphilic block copolymers; however, relatively few studies have been conducted using small-angle neutron scattering techniques to discover the mechanism by which they act. SANS results reported here show that a relatively simple core-shell cylinder model can be used to fit data successfully at different contrasts. The results across all contrasts showed that the best fit gave an inner nanotube radius of 10 Å, corresponding to small nanotube bundles with a small amount of water present (20%), and a polydisperse adsorbed layer thickness of 61 Å, with a water content of 94% in the adsorbed layer. The data fitting is thus consistent with a small SWCNT bundle surrounded by an extended and water-swollen F127 adsorbed layer. Comparing the scattering from F127/SWCNT at different contrasts, it has been found that the polymer-decorated SWCNTs are contrast matched at a D2O/H2O volume ratio of 0.36:0.64, corresponding to a scattering-length density of 1.92 × 10(-6) Å(-2).

PERFORMANCE ANALYSIS OF SWCNTS BUNDLES AND MWCNT INTERCONNECTS FOR SUBTHRESHOLD CIRCUITS

In this paper present the performance analysis of two possible realizations of a CNT-based nano-interconnect, namely one obtained by using a bundle of SWCNT and another one employing an MWCNT and their applicability as interconnects in nanoscale integrated circuits in subthreshold regime. The time delay, power dissipation and power delay product of SWCNT bundle and MWCNT interconnect configurations are derived and compared to those of the copper (Cu) wire counterparts for the intermediate and global interconnects for three different technologies (32-, 22- and 16nm). It is observed that, compared with the Cu, and SWCNT bundle the MWCNT interconnect can lead to a reduction of all above three parameters and it becomes more significant with increasing interconnect length. Because of considerable improvement in Power Delay Product MWCNT interconnect will be more suitable for the next generation of interconnect technology as compared with the SWCNT bundle and Cu counterpart in subthreshold regime also.

Electron diffraction and electron energy-loss spectroscopy studies of a hybrid material composed of coronene molecules encapsulated in single-walled carbon nanotubes

Electron diffraction and electron energy-loss spectroscopy (EELS) studies were conducted on bundles of single-walled carbon nanotubes encaging coronene molecules (coronenes@SWCNTs). Selected area electron diffraction (SAED) pattern of the coronenes@SWCNTs suggests that the coronene molecules inside the SWCNTs are separated into segments. Each segment is a stack consisting of ∼ 10 molecules and has a different tilted condition with respect to the nanotube axis. EELS spectra of the coronenes@SWCNTs show characteristic structures due to interband transitions between the van Hove singularities of the SWCNTs, and also π-plasmon and π + σ plasmon (volume plasmon) peaks. The volume plasmon energy of 23.0 eV for the coronene@SWCNTs is larger than that of an empty SWCNT bundle, indicating a contribution from the valence electrons of the coronene molecules. This value for the volume plasmon energy was reproduced using a model with an average of 85% filling of the SWCNTs by the coronene molecules. Therefore, both the SAED and EELS observations suggest that the SWCNTs are highly filled with coronene molecules. Further indication was that interband transition energies of coronene molecules of the present coronenes@SWCNTs material may be different from those in isolated ones and/or in solid state.

Structure–property–processing relationships of single-wall carbon nanotube thin film piezoresistive sensors

In an investigation of structure–property–processing relationships for SWCNT thin film piezoresistive sensors, the gauge factor of the sensors for a small tensile deformation (less than 2% strain) was found to be close to unity and showed negligible dependence on the film thickness and SWCNT bundle length (L) and diameter (d). However, for a large tensile deformation (20–30% strain), the film thickness and the microstructure of SWCNTs had a compounding effect on the piezoresistive behavior. A gauge factor of ∼5 was obtained for the sensors fabricated with SWCNT bundles of short length and thin diameter (L=549nm and d=3.7nm) with thicker films. Furthermore, the gauge factor of the sensors was found inversely proportional to the excluded volume Vex of SWCNT bundles (Vex∝1/L2d).

Transient analysis of mixed carbon nanotube bundle interconnects

Presented for the first time is an accurate modelling hierarchy for mixed CNT bundle interconnects. Single-walled CNTs and multi-walled CNTs have been modelled as equivalent single conductor transmission lines and then combined to form a mixed CNT bundle interconnect, which is basically a multiple equivalent single conductor model. Two multiple equivalent single conductor interconnects have been taken to form the multiconductor transmission line model. The delays from transient analysis for both models for a unit bundle have been compared with the corresponding ones for SWCNT bundles and MWCNTs that exist in the literature. It is found that mixed CNT bundle interconnects are superior to both SWCNT bundle and MWCNT interconnects in terms of delay.

Performance and Reliability Analysis of Bundled SWCNT as IC Interconnects

This work has investigated the performance of Single-walled carbon nanotube bundle as futuristic interconnect material under process constraints and compared its suitability as IC interconnect material as per ITRS predictions. It also analyzes variance of each parasitic effect along with the variations in process parameters. This paper pinpoints the variables causing bottlenecks in realizing optimum performance and improving reliability. It also evaluates the effect of diameter variations of CNTs in an SWCNT bundle and metallic tube ratio on the performance and reliability for 22nm technological node. The results demonstrate that the relative variations in the resistance are critically effected by the variations in metallic tube ratios rather than diameter variations. The diameter variation introduces its critical effect only at global level.

Crosstalk Prediction of Single- and Double-Walled Carbon-Nanotube (SWCNT/DWCNT) Bundle Interconnects

The crosstalk effects in single- and double-walled carbon-nanotube (SWCNT and DWCNT) bundle-interconnect architectures are investigated in this paper. Some modified equivalent-circuit models are proposed for both SWCNT and DWCNT bundles, where capacitive couplings between adjacent bundles are incorporated. These circuit models are further used to predict the performance of SWCNT and DWCNT bundle interconnects in comparison with the Cu wire counterpart at all interconnect levels for advanced future technology generations. It is found that, compared with the SWCNT bundle, the DWCNT bundle interconnect can lead to a reduction of crosstalk-induced time delay, which will be more significant with increasing bundle length, while the peak voltage of the crosstalk-induced glitch in SWCNT and DWCNT bundle interconnects is in the same order as that of Cu wires. Due to the improvement in time delay, it is numerically confirmed that the DWCNT bundle interconnect will be more suitable for the next generation of interconnect technology as compared with the SWCNT bundle counterpart.