Carbon nanotube based interconnect technology is becoming popular for its various merits over the current copper technology. The ability to conduct high current at high temperatures through the 1D structure is making the CNT interconnect technology an attractive one. Single wall and multi wall CNT interconnects have received greater interest initially when the mixed CNT bundles (MCBs) did not get much attention as VLSI interconnects. But, it was only in 2007 when the conductance study of mixed CNT bundles was done and since then many works have been reported. At this stage, it is essential to review the reports of MCB based interconnect technology. We present in this paper, the first review on MCB VLSI interconnects.

Uma Sathyakam P

Department of Instrumentation

School of Electrical Engineering

Vellore Campus

Partha Sharathi Mallick

Vellore Institute of Technology (VIT) is a private university located in&nbsp;Tamil Nadu, India. Founded in 1984, as Vellore Engineering College, the institution offers 20 undergraduate, 34 postgraduate, four integrated and four research programs. It has campuses in Vellore, Amravati, Bhopal and Chennai.

VIT is one of the top ranked private universities in India according to NIRF, THE and QS Rankings.&nbsp;Govt. of India has recognized&nbsp;VIT, Vellore as an&nbsp;Institution of Eminence. This has allowed VIT to take independent quality initiatives and move up in world ranking.

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VIT University

Nano Communication Networks

This paper proposes novel triangular cross-sectioned geometry of carbon nanotube (CNT) bundles for crosstalk and delay reduction in CNT bundle interconnects for VLSI circuits. First, we formulate the equivalent single conductor (ESC) transmission line models of the interconnects. Through SPICE analysis of the ESC circuits, we find the propagation delays of the proposed CNT bundles. Next, we model the capacitively coupled interconnects for crosstalk analysis. It is found that the coupling capacitance of triangular CNT bundle is 29% lesser than the traditionally used square CNT bundles. Further, the crosstalk-induced delay of triangular interconnects is found to be 30% lesser when compared to square bundle interconnects. The reduction in delay is found to increase as the number of CNTs in the bundle increases. So, we suggest that triangular CNT bundles are the most suitable candidates as global interconnects.

Fulltext

Journal of Circuits, Systems and Computers

Geometry-Based Crosstalk Reduction in CNT 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.

IET Circuits, Devices & Systems

High-speed sub-threshold operation of carbon nanotube interconnects

This paper proposes a body-biased bootstrapped CMOS driver for subthreshold applications. The proposed driver has been implemented with the same number of transistors as conventional bootstrapped CMOS driver. The performance of the subthreshold bootstrapped CMOS driver has been compared with the conventional bootstrapped CMOS driver. Our results show that the proposed body-biased subthreshold bootstrapped CMOS driver has 37% reduction in delay and 39% reduction in power dissipation compared to conventional bootstrapped CMOS driver. The proposed driver is more suitable to drive large loads compared to the conventional driver and operates better at subthreshold region.

Body-Biased Subthreshold Bootstrapped CMOS Driver

In this paper, we propose transmission gates (TGs) as buffers/repeaters for carbon nanotube (CNT)-based VLSI interconnects. Various performance metrics of the TG buffer, viz. propagation delay, crosstalk-induced delay, power dissipation, and power-delay product under super-threshold and sub-threshold conditions are analysed. Performance analysis of TG buffers with CMOS inverter buffers at various interconnect lengths and buffer insertion intervals is done. We have also analysed the performance of Single-wall carbon nanotube (SWCNT) bundle and three different configurations of mixed CNT bundles. By comparing the power-delay product of both the buffers, it is found that TG buffers are more suitable for applications in CNT-based integrated circuits.

IETE Journal of Research

Transmission Gate as Buffer for Carbon-Nanotube-Based VLSI Interconnects

Carbon nanotube (CNT) interconnects are emerging as the ultimate choice for next generation ultra large scale integrated (ULSI) circuits. Significant progress in precise growth of aligned CNTs and integration of multiwalled CNT interconnects into a test chip make them promising candidates for future nanoelectronic chips. Tremendous research efforts were made on silicon based ultra-low-k dielectrics for Cu interconnects, but, the most recent advancements in polymer based composites as dielectric materials open up fresh challenges in the use of low-k dielectrics for CNT interconnects. This paper reviews the emerging polymer composites like Boron Nitride Nanotubes, Graphene/Polyimide composites, Metal Organic Frameworks and small diameter CNTs. Many reviews are already exists on the synthesis, fabrication, dielectric, mechanical, chemical and thermal properties of these materials. In this review, we have explained the specific properties of these materials and the necessities for integrating them into CNT interconnects to meet the requirements of future IC designers.Keywords: low-k dielectric materials, ultra low-k dielectrics, carbon nanotubes, interconnects, dielectric constant,

Journal of Nano Research

Future Dielectric Materials for CNT Interconnects - Possibilities and Challenges

This article presents a realistic inter-carbon nanotube (CNT) electrostatic coupling capacitance and tunnelling conductance model for a mixed CNT bundle. The change of potential across such a bundle necessitates the need to consider the inter-CNT capacitance in the equivalent circuit of CNT interconnects for very large scale integration circuits. The equivalent transmission line circuit model of a unit bundle containing one single-walled CNT (SWCNT) and one multi-walled CNT (MWCNT) has been shown. This new model is then used to calculate the delay induced by the inter-CNT capacitance and tunnelling conductance, which predicts the relative positioning of MW/SWCNTs in mixed CNT bundle.

International Journal of Electronics

Inter-CNT capacitance in mixed CNT bundle interconnects for VLSI circuits

The change of potential across a CNT in a bundle necessitates the need to consider the inter-CNT coupling capacitance in the equivalent circuit of CNT interconnects for VLSI circuits. This paper presents a realistic inter-CNT electrostatic coupling capacitance and tunneling conductance model for this bundle and studied its effects in detail. The equivalent transmission line circuit model of a unit bundle containing one SWCNT and one MWCNT has been shown. This new model is then used to calculate the delay induced by the inter-CNT capacitance and tunneling conductance, which predicts the relative positioning of MW/SWCNTs in mixed CNT bundle.

2011 International Conference on Nanoscience, Technology and Societal Implications

Effect of Realistic Inter-CNT Coupling Capacitance in Mixed CNT Bundle

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.

Journal	Data powered by TypesetNano Communication Networks
Publisher	Data powered by TypesetElsevier BV
ISSN	1878-7789
Open Access	0