This approach has broader applications and could be adapted for other advanced field-effect transistor channel materials, including two-dimensional semiconductors.~ Researchers.
The team at the University of California, San Diego, in collaboration with the Taiwan Semiconductor Manufacturing Company, has recently created new carbon nanotube metal-oxide-semiconductor field-effect transistors (MOSFETs) using localised solid-state extension doping.
One-dimensional semiconductors like carbon nanotubes offer the potential to reduce the gate length of metal–oxide–semiconductor field-effect transistors (MOSFETs) beyond what is achievable with silicon-based transistors. However, creating industry-compatible doping methods and controlling the polarity of these devices is a complex challenge.
These top-gate complementary carbon nanotube MOSFETs have been developed using localised conformal solid-state extension doping to determine device polarity and ensure balanced performance. In these transistors, the channel remains undoped.
This allows for the achievement of complementary metal oxide semiconductor or CMOS-compatible threshold voltages for n- and p-MOSFETs at +0.29 V and -0.25 V, respectively. The fabrication process, which is compatible with standard industry practices, employs localised charge transfer.
This transfer occurs from defect levels in silicon nitride (SiNx) for n-type devices or from an electrostatic dipole at the SiNx/aluminium oxide (Al2O3) interface for p-type devices. The SiNx donor defect densities can reach up to 5 × 10¹⁹ cm⁻³, potentially supporting carbon nanotube carrier densities of 0.4 nm⁻¹ in the extensions of scaled nanotube devices.