Omni 3D: BEOL-Compatible 3-D Logic With Omnipresent Power, Signal, and Clock

Abstract

This article presents Omni 3D—a 3-D-stacked device architecture that is naturally enabled by back-end-of-line (BEOL)-compatible transistors. Omni 3D interleaves metal layers with 3-D-stacked nFETs and pFETs. Thus, the signal and power routing layers have fine-grained, all-sided access to the field-effect transistor (FET) active regions maximizing 3-D standard cell design flexibility. This is in sharp contrast to approaches such as back-side power delivery network (BSPDN), complementary FETs (CFETs), and stacked FETs. Importantly, the routing flexibility of Omni 3D is enabled by double-side metal and interleaved metal (IM) for inter- and intracell routing, respectively. In this work, we explore Omni 3D variants (e.g., both with and without the IM) and optimize these variants using a virtual-source BEOL-FET compact model. We establish a physical design flow that efficiently uses the double-side routing in Omni 3D and perform a thorough design technology co-optimization (DTCO) of Omni 3D device architecture on several design points. From our design flow, we project ${2.0}\times $ improvement in the energy-delay product (EDP) and ${1.5}\times $ reduction in area on average across our benchmark circuits compared with the state-of-the-art CFETs with BSPDN.