Clock Tree Insertion and Verification for 3D Integrated Circuits

Abstract

The use of three dimensional chip fabrication technologies has emerged as a solution to the difficulties involved with the continued scaling of bulk silicon devices. While the technology exists, it is undervalued and underutilized largely due to the design and verification challenges a complex 3D design presents. This work presents a clock tree insertion and timing verification methodology for three dimensional integrated circuits (3DIC). It has been designed in the context of and incorporated into the 3DIC design methodology also developed within our research group. The 3DIC verification methodology serves as an efficient means to perform all setup and hold timing checks harnessing the power of existing commercial chip design and verification tools. A novel approach is presented in which the multi-die design is temporarily transformed to appear as a traditional 2D design to the commercial tools for verification purposes. Various parasitic extraction algorithms are examined, and we present a method for performing accurate 3D parasitic extraction for timing purposes. We offer theoretical insight into the optimization of a 3D clock tree for power savings and coupling-induced delay minimization. A practical example of the 3DIC design and verification flow is detailed through the explanation of our research group's test chip, a nearly 140,000 cell 3D fast Fourier transform chip currently awaiting fabrication at MIT's Lincoln Labs.