Topological failure mode taxonomy and variation-aware design space exploration of carbon nanotube field-effect...

Carbon Nanotube Field-Effect Transistors (CNTFETs) represent a promising post-CMOS technology, yet their adoption in sequential logic remains hindered by device-level non-idealities. This work presents a comprehensive device-to-system evaluation of flip-flop topologies in 32nm CNTFET technology using the Stanford compact model. N-type and p-type CNTFET I-V characteristics are characterized across three chiral vectors, establishing physical design constraints. Screening 25 flip-flop architectures from recent literature identifies that only 11 (44%) maintain functionality in CNTFET, with failure modes attributed to threshold voltage asymmetry, ambipolar conduction, and insufficient drive current. The 11 functional topologies undergo rigorous multi-corner analysis: voltage scaling (0.7-1.1 V), chirality variation, data activity dependence, and 200-run Monte Carlo simulations with 10% standard deviation in channel length, oxide thickness, and pitch. System-level validation via a 3-bit shift register confirms cascadability for robust designs while revealing functional failures in three topologies that operated correctly in isolation. Among all candidates, Lin's FF achieves optimal energy efficiency (0.046 aJ) with robust corner-to-corner operation, while Mishra's FF demonstrates superior variation tolerance (81.5% Monte Carlo yield). Eight actionable design guidelines are distilled for CNTFET sequential circuits, including prioritization of TSPC architectures, avoidance of ratioed logic, and early chirality-aware validation. This study provides a foundational reference for emerging-technology digital design, demonstrating that careful topology selection enables robust, energy-efficient sequential logic in CNTFET technology despite significant device-level challenges.