System-level performance evaluation of three-dimensional integrated circuits

Abstract

As the critical dimensions in VLSI design continue to shrink, system performance of integrated circuits (ICs) will be increasingly dominated by interconnect delay [1]. For the technology generations approaching 50 nm and beyond, innovative system architectures and interconnect technologies will be required to meet the projected system performance [2]. Interconnect material solutions such as copper and low-k inter-level dielectric (ILD) offer only a limited improvement in system performance. Significant and scalable solutions to the interconnect delay problem will require fundamental changes in system design, architecture, and fabrication technologies. Three-dimensional (3-D) ICs can alleviate interconnect delay problems by offering flexibility in system design, placement and routing. They (3-D ICs) can be formed by vertical integration of multiple device layers using wafer bonding, recrystallization, or selective epitaxial growth. The flexibility to place devices along the vertical dimension allows higher device density and smaller form factor in 3-D ICs. The critical signal path that may limit system performance can also be shortened to achieve faster clock speed. By 3-D integration, device layers fabricated with different front-end process technologies can be stacked along the 3rd dimension to form systems-on-a-chip [3]. In this thesis work, opportunities and challenges for 3-D integration of logic networks, microprocessors, and programmable logic have been explored based on system-level modeling and analysis. A stochastic wire-length distribution model has been derived to predict interconnection complexity in 3-D ICs. As more device layers are integrated, the 3-D wire-length distribution becomes narrower compared to that of 2-D ICs, resulting in a significant reduction in the number and length of semi-global and global wires. In 3-D ICs with 2-4 device layers, 30% - 50% reduction in wire-length can be achieved. Besides performance modeling, thermal analysis has also been performed to assess power dissipation and heat removal issues in 3-D ICs. The total capacitance associated with signal interconnects and clock networks can be reduced by 3-D integration, leading to lower power dissipation for system performance comparable to that of 2-D ICs. However, for higher system performance in 3-D ICs, power dissipation increases significantly, and it is likely that innovative cooling techniques will be needed for reliable operation of devices and interconnects.