Statistical analysis for on-chip power grid networks and interconnects considering process variation.

摘要

With the aggressive scaling down of semiconductor VLSI devices from 65nm to 45 nm, 32nm, the process induced variability becomes the major design concern. The fundamental change in VLSI chip design in current and future nodes is that what has been designed will not agree with the products manufactured due to the uncertainties in the manufacture processes. Even worse, the variabilities keep growing as the technology scales down continually. The process induced variations manifest themselves from wafer to wafer, die-to-die and device to device within a die. Some are systematic variabilities and some are random variabilities, which have to leave extra margin for worst case. The Monte Carlo method can come to the rescue by simulating the probability of the worst case in a random way. However, it is well known this approach is very time consuming and forbidding slow. It is highly desirable to have more efficient statistical modeling and simulation techniques and tools to guide the design in the presence of uncertainties in the nanometer VLSI regime.;In this dissertation, the influence of the variability, such as threshold voltage variation, interconnect wire height, width variation, on the performance of power grid delivery networks and signal interconnect circuits, are studied. First we develop a new statistical method, which is based on concept of Hermite polynomial chaos, to analyze power grid voltage drop variations of on-chip power grid networks. The new approach considers both wire variations and sub-threshold leakage current variations, which are modeled as lognormal distribution random variables. We also consider spacial correlation of the leakage variables by applying orthogonal decomposition to map the correlated random variables into independent ones before the analysis. Second, we propose a more efficient statistical analysis approach, StoEKS, in which the extended Krylov subspace method is used to speedup the solution procedure of the variational circuit equations. By using the model order reduction technique, StoEKS partially mitigates circuit-size increasing problem associated with the augmented matrices from the Galerkin-based spectral statistical method. Finally, we propose an efficient method to calculate variational interconnect delay, which is a crucial step in the statistical static timing analysis(SSTA). We apply Numerical quadrature method based on orthogonal polynomial representation (OPR) of statistical variations to derive the non-linear, non-Gaussian analytic interconnect delay models in terms of the interconnect wire width, height variations. It can take in variational parameters in OPR form and outputs the delays computed in OPR form again, which is compatible with existing SSTA methods.