VLSI-compatible carbon nanotube doping technique with low work-function metal oxides.

Area of Science:

• Materials Science
• Nanotechnology
• Semiconductor Physics

Background:

• Single-wall carbon nanotubes (SWCNTs) are promising for high-speed transistors.
• Existing carbon nanotube field-effect transistors (CNFETs) are typically p-type.
• A scalable, reproducible n-type doping method for carbon nanotubes (CNTs) is crucial for complementary circuits.

Purpose of the Study:

• To present a novel, wafer-scale, solid-state doping technique for fabricating n-type CNT transistors.
• To demonstrate the efficacy of low work-function metal oxides as gate dielectrics for n-type doping.
• To enable the development of complementary logic circuits using CNTs.

Main Methods:

• Fabrication of aligned CNT transistors using yttrium oxide (Y2Ox) as a gate dielectric.
• Characterization using atomic force microscopy (AFM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD).
• Testing of transistor performance, including on/off current ratio (Ion/Ioff) and inverse subthreshold slope.

Main Results:

• Demonstrated wafer-scale, aligned CNT transistors exhibiting n-type behavior with an Ion/Ioff of 10^6 and an inverse subthreshold slope of 95 mV/dec.
• Confirmed that slow evaporation of yttrium forms a smooth surface, enabling excellent wetting on CNTs.
• XPS and XRD analysis revealed that partially oxidized yttrium acts as a reducing agent, donating electrons for n-type doping.

Conclusions:

• The presented VLSI-compatible doping technique effectively produces n-type CNT transistors using low work-function metal oxides.
• The mechanism involves electron donation from partially oxidized yttrium, leading to n-type doping.
• This method is extendable to other low work-function metals (La, Er, Sc), paving the way for complementary CNT transistor technology.