Improving Contact Resistance in Top-Gate Carbon Nanotube Transistor through Self-Aligned MoO _<i>x</i> Nanoparticle Contact Doping

Carbon nanotubes (CNTs) are promising candidates for next-generation back-end-of-line (BEOL) compatible devices due to their excellent scalability, energy efficiency, compatibility with low-temperature processes, and high-speed charge transport. However, top-gate carbon nanotube field-effect transistors (CNFETs) often suffer from high contact resistance RC, which significantly reduces the on-state current and hinders the realization of high-performance devices. This is primarily attributed to gate-field screening at the contact–channel interface, which increases RC compared to their back-gate counterparts. In this work, we address this limitation through a combination of numerical modeling and experimental validation using self-aligned contact doping enabled by MoOx nanoparticles. A self-consistent one-dimensional Poisson solver coupled with the Landauer–Büttiker formalism reveals that contact doping improves the Schottky barrier and enhances carrier tunneling. Experimentally, top-gate CNFETs with 0.8 nm MoOx-doped Pd contacts exhibit a 58% reduction in RC, a significant increase in output current, and a reduction in effective Schottky barrier height from 72 to 20 meV, while maintaining long-term stability for over 71 days. Furthermore, Monte Carlo simulations incorporating realistic CNT diameter distributions predict a reduction of up to 52% in dense CNT arrays with a diameter of 1.0 nm. This study provides both fundamental insight and experimental demonstration of self-aligned MoOx contact doping as a scalable strategy to mitigate contact resistance in top-gate CNFETs.