Overcoming Ambient Drift and Negative-Bias Temperature Instability in Foundry Carbon Nanotube Transistors

Carbon nanotube field-effect transistors (CNFETs) are promising candidates for back-end-of-line logic integration as a complementary path for continued electronic scaling. However, overcoming CNFET ambient drift (i.e., air stability) and reliability is underexplored. Here, we demonstrate that silicon nitride encapsulation limits ambient atmosphere-induced threshold voltage shift (∼8× reduction of median ΔV_T over 90 days). With stabilized nitride-encapsulated CNFETs, we characterize CNFET negative bias temperature instability (NBTI) with both DC and AC stress across the electric field, temperature, gate oxide thickness, and stress frequency. AC pulsed operation significantly improves CNFET NBTI vs DC operation across a wide frequency range of 1 kHz-10 MHz. A 20% duty cycle AC operation at 10 MHz could extend the NBTI time to failure by > 10⁴× vs DC for a target |ΔV_T| tolerance ≤100 mV with a gate bias V_GS,Stress = -1.2 V at 125 °C. This work improves our understanding of overcoming ambient drift and BTI reliability in CNFETs.