EFFECT OF CHANGE OF DIAMETER RATIO ON PERFORMANCE OF MWCNTS AS VLSI INTERCONNECTS

Abstract

ABSTRACT According to the Moore's law, the number of transistors and densities on integrated circuits doubles approximately every two years. Hence as per Moore’s law, the dimensions and performance of devices are scaling down over the last 40 years. Due to scaling, performance of on-chip intermediate length copper interconnect faces many challenges such as using copper as interconnect the speed of device getting slower, power consumption increasing and the requirement of bandwidth does not fulfilled. As technology scales down the problems associated with copper as interconnects are low mean free path, electro migration and high resistivity due to rough surface and grain boundary scattering. The most promising solution of copper problem is Carbon Nanotubes (CNT) for future integrated circuits. As CNTs have good electrical properties, high thermal and mechanical strength. CNTs have long mean free paths (MFPs) on the order of several micro meters as compared to Copper at room temperature, which provide low resistivity and possible ballistic transport in intermediate-length interconnects. An isolated CNT can carry current densities in excess of 1010 A/cm2 without any signs of damage, thereby eliminating electromigration reliability concerns that plague nanoscale Copper interconnects. CNTs are classified as SWCNT (Single-walled Carbon Nanotube) and MWCNT (Multi-walled Carbon Nanotube). SWCNT consists of single shell of graphene sheet, it can have diameters varying from few nanometers to 4nm. MWCNTs is consists of multiple concentric shells of graphene sheets. In this thesis work, the performance of MWCNTs and Copper has been compared at 32nm, 22nm and 16nm technology node at intermediate level of interconnect. The model of MWCNT and Copper as interconnect used for delay calculation has been estimated. Changing the diameter ratio leads to change in number of shell. As the diameter ratio increases this means the number of shell decreases. As the number of shells increases then the number of conducting channels increases. This leads to increase in conductivity of MWCNT, hence decrease in resistivity of MWCNT. The diameter ratio of MWCNT has been varied for all of three technologies to compare performance parameter i.e. delay, power consumption and power delay product(PDP) with respect to copper as interconnect at intermediate level. It is shown that MWCNT gives better result than copper interconnects at intermediate level. Even that the worst case of MWCNT as interconnect provides better performance than copper.