Modeling Crosstalk Effects in CNT Bus Architectures

Carbon nanotubes (CNTs) have been widely proposed as interconnect fabric for nano and very deep submicron (silicon-based) technologies due to their robustness to electromigration. In this paper, issues associated with crosstalk among bus lines implemented by CNTs are investigated in detail. CNT-based interconnects are modeled and the effects of crosstalk on performance and correct operation are evaluated by simulation. Existing models are modified to account for geometries in bus architectures made of parallel single-walled nanotubes and a single multiwalled nanotube. New RLC equivalent circuits are proposed for these bus architectures. A novel bus architecture with low crosstalk features is also proposed. This bus architecture is made of dual-walled nanotubes arranged in parallel. In this architecture, the crosstalk-induced delay and corresponding uncertainty (as well as crosstalk-induced peak voltage) are significantly reduced; a modest area penalty is incurred. Reductions up to 59% for the crosstalk-induced delay and up to 81% for the crosstalk-induced peak voltage are reported. These results confirm that the proposed bus arrangement noticeably improves performance and provides reliable operation.

I. Introduction

Global interconnects (such as the so-called bus) are widely employed to distribute data, clock, power supply, and ground throughout the entire area of an integrated circuit (IC). At high current density, most materials used in today's interconnects (such as Al and Cu) [1] are affected by electromigration, thus substantially impacting reliability (as measured by the correct operation of the IC). The ITRS Roadmap [2] emphasizes the need for reliable high-speed interconnects for VLSI as well as emerging technologies and suggests the need for innovative materials and process solutions for investigation; moreover, this still remains a very challenging problem due to the tight constraints on the reliable operation and fast operating speed of these ICs. Carbon nanotubes (CNTs) offer unique capabilities due to their conductive, mechanical, and thermal properties [1]. CNTs have been proposed for providing signals for clocking quantum-dot cellular automata (QCA) circuits [3]. These devices can be classified as single-walled nanotubes (SWNTs) and multiwalled nanotubes (MWNTs). SWNTs consist of a single sheet of graphene rolled up into a cylindrical tube that can have a diameter in the nanometer range and a length in the micrometer range [4]. MWNTs consist of two or more SWNTs, which are concentrically wrapped one over the other [4]. Depending on the direction in which they are rolled (referred to as chirality), CNTs can behave either as a semiconductor or a conductor [5]. Semiconductive nanotubes can be employed for the channel of carbon nanotube field-effect transistors (CNFETs) [6]. Conductive (or metallic) nanotubes are envisioned as ideal interconnect devices for emerging technologies at nano scale as well as for today's very deep submicron (silicon-based) electronics [6]–[12].