Multi-walled Carbon Nanotube Bundle Interconnects Research Articles

Efficient Passive Shielding of MWCNT Interconnects to Reduce Crosstalk Effects in Multiple-Valued Logic Circuits

In this paper, the effectiveness of passive shielding of multiwalled carbon nanotube (MWCNT) bundle interconnects in reducing the crosstalk effects in carbon nanotube FET based ternary circuits is comprehensively investigated. In addition, based on the tighter sublithographic pitch of MWCNTs compared to Cu, we decrease the space between the carbon nanotube (CNT) interconnects to reduce the area overhead, while still having significantly higher effectiveness compared with Cu. The worst-case crosstalk delay and noise for passively shielded MWCNT and Cu wires at 14 nm technology are evaluated using comprehensive HSPICE simulations. The results indicate that the crosstalk delay and noise area in the efficient passively shielded MWCNT bundle interconnects are much smaller than the shielded Cu wires for ternary logic. Furthermore, the impacts of process variation on the crosstalk effects in these interconnects in ternary logic are investigated using Monte Carlo simulations. The results demonstrate the robustness of the passively shielded MWCNT bundles in ternary logic.

Active Shielding of MWCNT Bundle Interconnects: An Efficient Approach to Cancellation of Crosstalk-Induced Functional Failures in Ternary Logic

This study presents an efficient geometry for active shielding of multiwalled carbon nanotube (MWCNT) bundle interconnects which cancels the crosstalk-induced functional failures in ternary logic. In this geometry, MWCNT bundles are used innovatively as shields on both sides of the signal transmission line to reduce the crosstalk effects while maintaining the minimum interconnect pitch. Simulations are performed using HSPICE for intermediate and global interconnects in ternary logic at 14-nm node. The results indicate that the crosstalk-induced functional failure in ternary logic is omitted by using the proposed structure. Moreover, according to the results, our proposed geometry reduces the crosstalk noise peak as compared to the widened MWCNT bundles, distanced MWCNT bundles and Cu interconnects on average by 41%, 44%, and 61% for the intermediate interconnects and 61%, 46%, and 74% for the global interconnects, respectively, without any considerable power consumption penalties.

Bandwidth expanding technology for dynamic crosstalk aware single-walled and multi-walled carbon nanotube bundle interconnects

In view of scarce bandwidth resources, an inductive peaking technology is used to expand 3-dB bandwidth of the coupled single-walled and multi-walled carbon nanotube bundle interconnects, which take the dynamic crosstalk into account. Based on decoupling technique and ABCD parameter matrix approach, the transfer function of the decoupled victim line at global level of 14 nm technology node is derived to analyze and compare the bandwidth performance under different length, diameter, temperature and load resistance conditions. It is obvious that 3-dB bandwidth can be effectively expanded by adding peaking inductance to the load irrespective of phase-mode. However, the bandwidth will remain nearly unchanged once the adding inductance reaches a certain extent. Furthermore, the overshoot and undershoot in the step response will be caused with the further increase of the peaking inductance. On the other hand, it is shown that the value of 3-dB bandwidth at out-of-phase mode is much smaller than that at in-phase mode under the same condition.

Analysis of Crosstalk Effects for Multiwalled Carbon Nanotube Bundle Interconnects in Ternary Logic and Comparison with Cu interconnects

In this study, the crosstalk-induced effects are investigated in ternary logic by using the three-line bus architecture. The worst case crosstalk delays for both repeated and unrepeated interconnect and the peak crosstalk noise voltage on the victim net are investigated. Analyses have been done for global level multiwalled carbon nanotube (MWCNT) bundle and copper interconnects with carbon nanotube FET-based drivers and receivers at 22 nm node. According to the HSPICE simulations, the crosstalk delay and noise area in the MWCNT bundle interconnects are much smaller than the Cu wires for the ternary logic. In addition, the MWCNT bundle interconnects require a lower number of repeaters as compared to the Cu wires, which results in lower complexity and power consumption. The results indicate that utilizing the MWCNT interconnects instead of Cu wires in ternary systems leads to 63% shorter crosstalk delay without repeater insertion and 65% lower crosstalk noise area and 75% lower power consumption with repeater insertion. It is concluded from the results that the MWCNT bundle global wires are more suitable for ternary very large scale integration systems as compared to the Cu wires.

Temperature-Dependent Modeling and Performance Evaluation of Multi-Walled CNT and Single-Walled CNT as Global Interconnects

The influence of temperature on multi-walled carbon nanotube (MWCNT) interconnects have been studied. A temperature-dependent equivalent circuit model is presented for the impedance parameters of MWCNT bundle interconnects that captures various electron–phonon scattering mechanisms as a function of temperature. To estimate the performance of MWCNT bundle interconnects, the signal delay, power dissipation and power delay product (PDP) were simulated based on a temperature-dependent model that results in improvement in the delay, power and PDP estimation accuracy compared to the temperature-independent model. The results revealed that the power delay product of MWCNT bundle interconnects increases with increasing temperature from 200 K to 450 K for three different technology nodes, i.e., 32 nm, 22 nm and 16 nm, based upon a 1000-μm interconnect length. A similar analysis was performed for single-walled carbon nanotube (SWCNT) bundle interconnects and the results are compared with MWCNT bundle interconnects, indicating that the delay, power and power delay product (PDP) also increased with increasing temperature from 200 K to 450 K. The interconnects of the MWCNT bundle interconnects gave a better performance in terms of delay, power and PDP as compared to the SWCNT bundle interconnects.

Modeling and Analysis of Crosstalk Induced Effects in Multiwalled Carbon Nanotube Bundle Interconnects: An ABCD Parameter-Based Approach

In this paper, the crosstalk effects in both small and large diameter multiwalled carbon nanotube bundle interconnects (MWCNTs) for the future nanoscale integrated circuits are studied with the help of ABCD parameter matrix approach for global levels of interconnects at 22- and 14-nm technology nodes. Here, isolated MWCNTs are modeled using an equivalent single conductor transmission line. The simulation results show that the results are at par with the result of SPICE model. It is observed that performance wise, the large diameter MWCNT bundles are better than both small diameter MWCNT bundles and copper wire for both repeated and unrepeated interconnects. The same trend is observed with the number of inserted repeaters. For repeated wires, the optimized placement of repeaters offsets the delay advantage numbers of MWCNT bundles over copper wire. Technology scaling adversely impacts the delay advantage numbers of small diameter MWCNT bundles. As far as the worst-case crosstalk noise peak voltage is concerned, the large diameter MWCNT bundles also outperform both small diameter MWCNT bundles and copper wire for longer interconnects. However, for shorter interconnects, copper wire and small diameter bundles outclass the large diameter bundles due to their relatively larger time constant. We have compared our crosstalk analysis results with the earlier work to justify the validity of our proposed model and observed that the results with our model are in well conformity with the existing work. It is seen that even the tall Cu vias are not going to significantly affect the performance of MWCNT bundle interconnects. Twice the minimum width global level interconnects are the optimal choice to achieve the maximum delay advantage using MWCNT bundle interconnects in comparison with Cu-based interconnects. Finally, our analysis shows that from the performance and signal integrity perspective, the large diameter MWCNT bundles are a suitable alternative to both small diameter MWCNT bundles and copper interconnects for future integrated circuit technology generations.

Delay and crosstalk reliability issues in mixed MWCNT bundle interconnects

Multi-walled carbon nanotube (MWCNT) bundles have potentially provided attractive solution in nanoscale VLSI interconnects. In current fabrication process, it is not trivial to grow a densely packed bundle having MWCNTs with similar number of shells. A realistic nanotube bundle, in fact, is a mixed CNT bundle consisting of MWCNTs of different diameters. This research paper presents an analytical model of mixed CNT bundle wherein MWCNTs having different number of shells are densely packed. Two different types of MWCNT bundles are presented: (1) MB that contains MWCNTs with similar number of shells (i.e., uniform diameters) and (2) MMB wherein MWCNTs having different number of shells (i.e., non-uniform diameters) are mixed. Multi-conductor transmission line theory is used to present an equivalent single-conductor (ESC) model of different MB and MMB configurations. Using the ESC model, performance is analyzed to address the effect of propagation delay, crosstalk and power dissipation that explores the reliability of an interconnect wire. It is observed that using an MMB arrangement, the overall reduction in delay and crosstalk are 15.33% and 29.59%, respectively, compared to the MB for almost similar power dissipation.