Study the Temperature-Dependent Modeling and Performance Analysis of Mixed Carbon Nanotube (CNT) Bundle Based VLSI Interconnects

Abstract

The resistance of copper (Cu) interconnect is increasing with advancement of technology nodes in deep submicron (DSM) which causes degradation in interconnect performances in terms of crosstalk and propagation delay. Recent research shows that the carbon nanotubes (CNT) are preferred over Cu interconnects due to their high current carrying capacity and high thermal conductivity. CNT has high equivalent resistance but it reduces to very small value when it used in bundle. However, a realistic CNT bundle contains a mix of Single walled carbon nanotubes (SWCNTs) and Multi walled carbon nanotubes (MWCNTs). So, many researchers proposed different structures of mixed CNT bundle (MCB) based on the different arrangements of SWCNT and MWCNT. Currently primary focus of researchers is on the performance analysis of different structures of MCB. Beyond 45nm technology node, due to temperature variation there is significant change in the performance of the CNT based interconnects. So temperature-dependent performance analysis of interconnects is very important. A lot of research has been done for the temperature-dependent analysis of SWCNT and MWCNT individually. However no analysis has been made to analyze temperature-dependent performance analysis for coupled mixed CNT bundle based interconnects. In this thesis, the temperature-dependent circuit modeling and performance analysis in terms of crosstalk in capacitively coupled MCB interconnects, at the far end of victim line, have been analyzed with four different structures of mixed CNT bundles (MCB-1, MCB-2, MCB-3 and MCB-4) constituted under case-1 and case-2 at 22 nm technology node. The impact of tunneling and intershell coupling between neighbouring shells on temperature–dependent equivalent circuit parameters of an MWCNT bundle are also critically analyzed and employed for different structures of MCBs under case-1. A similar analysis is performed for Cu interconnects and comparisons are made between results obtained through these analyses over a temperature ranging from 300K to 500K. iv The SPICE simulation results reveal that, compared with all structures of MCBs under case-1 and case-2, with rise in temperature from 300K to 500K, crosstalk -induced noise voltage levels at the far end of victim line, are found to be significantly large in Cu. It is also observed that due to the dominance of larger temperature-dependent resistance and ground capacitance in case-1, the MCB-2 is of lower crosstalk-induced noise voltage levels than other structures of MCBs. On the other hand, the MCB-1 has smaller time duration of victim output. Results further reveal that, compared with case- 2 of MCB, with rise in temperatures, the victim line gets less prone to crosstalkinduced noise in MCB interconnects constituted under case-1, due to tunneling effects and intershell coupling between neighbouring shells. Based on these comparative results, a promising structure of mixed CNT bundle (MCB-2) has been proposed among other structures under the consideration of tunneling effects and intershell coupling (case-1).