Migration to 3-D provides a possible pathway for future Integrated Circuits (ICs) beyond 2-D CMOS, which is at the brink of its own fundamental limits. Partial attempts so far for 3-D integration using die to die and layer to layer stacking do not represent true progression , and suffer from their own challenges with lack of intrinsic thermal management being among the major ones. Our proposal for 3-D IC, Skybridge, is a truly fine-grained vertical nanowire based fabric that solves technology scaling challenges, and at the same time achieves orders of magnitude benefits over 2-D CMOS.

Nanoscale 3D-integrated Application Specific ICs (N3ASICs) [1], a computing fabric based on semiconductor nanowire grids, is targeted as a scalable alternative to end-of-the-line CMOS. In contrast to device-centric approaches like CMOS, N3ASIC design choices across device, circuit and architecture levels are geared towards reducing manufacturing requirements while focusing on overall benefits.

Several nanoscale-computing fabrics based on novel materials such as semiconductor nanowires, carbon nanotubes, graphene, etc. have been proposed in recent years. However, their integration and interfacing with external CMOS has received only limited attention. In this paper we explore integration challenges for nanoscale fabrics focusing on registration and overlay requirements especially. We address the following questions: (i) How can we mitigate the overlay requirements between nano-manufacturing and conventional lithography steps?

CMOS faces new device and technology challenges: MOSFETs require ultra-sharp doping profiles and complex processing; integration of devices into circuits requires arbitrary interconnection with overlay precision beyond known manufacturing solutions (3σ=±3nm, 16nm CMOS, ITRS’11[1]). To overcome these challenges, we propose a new nanoscale computing fabric with integrated design of device, interconnect and circuits to minimize manufacturing requirements while providing ultra-dense, high-performance, and low-power solution surpassing scaled CMOS.