Rapid approximation of the transient response of high-speed global interconnects is needed to estimate the time delay, crosstalk, and overshoot in a GSI multilevel wiring network. This paper outlines a rigorous and physical solution for transients in a capacitively-loaded distributed rlc interconnect using a convergent series of modified Bessel functions. Compact models for time delay and repeater insertion are derived. The single-line model is extended to evaluate crosstalk in two-coupled lines. These solutions are validated by HSPICE simulation, and have potential applications to rapid rlc timing analysis, global wire sizing and repeater insertion, signal integrity estimation, and reliability modeling (e.g. voltage overshoot and high current density concerns).

Twenty-first century opportunities for GSI will be governed in part by a hierarchy of physical limits on interconnects whose levels are codified as fundamental, material, device, circuit, and system. Fundamental limits are derived from the basic axioms of electromagnetic, communication, and thermodynamic theories, which immutably restrict interconnect performance, energy dissipation, and noise reduction. At the material level, the conductor resistivity increases substantially in sub-50-nm technology due to scattering mechanisms that are controlled by quantum mechanical phenomena and structural/morphological effects. At the device and circuit level, interconnect scaling significantly increases interconnect crosstalk and latency. Reverse scaling of global interconnects causes inductance to influence on-chip interconnect transients such that even with ideal return paths, mutual inductance increases crosstalk by up to 60% over that predicted by conventional RC models. At the system level, the number of metal levels explodes for highly connected 2-D logic megacells that double in size every two years such that by 2014 the number is significantly larger than ITRS projections. This result emphasizes that changes in design, technology, and architecture are needed to cope with the onslaught of wiring demands. One potential solution is 3-D integration of transistors, which is expected to significantly improve interconnect performance. Increasing the number of active layers, including the use of separate layers for repeaters, and optimizing the wiring network, yields an improvement in interconnect performance of up to 145% at the 50-nm node.

An interconnect distribution model for homogeneous, three-dimensional (3-D) architectures with variable separation of strata is presented. Three-dimensional architectures offer an opportunity to reduce the length of the longest interconnects. The separation of strata has little impact on the length of interconnects but a large impact on the number of interstratal interconnects. Using a multilevel interconnect methodology for an ITRS 2005 100 nm ASIC, a two-strata architecture offers a 3.9/spl times/ increase in wire-limited clock frequency, an 84% decrease in wire-limited area or a 25% decrease in the number of metal levels required. In practice, however, such fabrication advances as improved alignment tolerances in wafer-bonding techniques are needed to gain key advantages stemming from 3-D architectures for homogeneous gigascale integrated circuits.

A multilevel interconnect architecture design methodology that optimizes the interconnect cross-sectional dimensions of each metal layer is introduced that reduces logic macrocell area, cycle time, power consumption or number of metal layers. The predictive capability of this methodology, which is based on a stochastic wiring distribution, provides insight into defining the process technology parameters for current and future generations of microprocessors and application-specific integrated circuits (ASICs). Using this methodology on an ASIC logic macrocell case study for the 100 nm technology generation, the optimized n-tier multilevel interconnect architecture reduces macrocell area by 32%, cycle time by 16% or number of wiring tracks required on the topmost tier by 62% compared to a conventional design where pitches are doubled for every successive pair of levels. A new repeater insertion methodology is also described that further enhances gigascale integration (GSI) system performance. By using repeaters, a further reduction of 70% in macrocell area, 18% in cycle time, 25% in number of metal levels or 44% in power dissipation is achieved, when compared to an n-tier design without repeaters. The key distinguishing feature of the methodology is its comprehensive framework that simultaneously solves two distinct problems-optimal wire sizing and wiring layer assignment-using independent constraints on maximum repeater area for efficient design space exploration to optimize the area, power, frequency, and metal levels of a GSI logic megacell.

Minimum power CMOS ASIC macrocells are designed by minimizing the macrocell area using a new methodology to optimally insert repeaters for n-tier multilevel interconnect architectures. The minimum macrocell area and power dissipation are projected for the 100, 70 and 50 nm technology generations and compared with a n-tier design without using repeaters. Repeater insertion and a novel interconnect geometry scaling technique decrease the power dissipation by 58-68% corresponding to a macrocell area reduction of 70-78% for the global clock frequency designs of these three technology generations.