Two-Dimensional Vertical Transistor with One-Dimensional van der Waals Contact.

Area of Science:

• Materials Science
• Nanotechnology
• Electronics Engineering

Background:

• Two-dimensional (2D) materials offer a path for scaling down transistors via vertical field-effect transistors (VFETs).
• A significant challenge in VFET scaling is the short channel effect as 2D material thickness approaches ~10 nm.
• Existing contact methods struggle to maintain performance in ultrathin channels.

Purpose of the Study:

• To demonstrate the feasibility of using semimetal carbon nanotubes (CNTs) as 1D van der Waals (vdW) contacts in VFETs.
• To investigate the performance of VFETs with ultrashort 2D channels and CNT contacts.
• To analyze the mechanisms behind the improved performance in CNT-contacted VFETs.

Main Methods:

• Fabrication of VFETs using transition metal dichalcogenide (e.g., MoS2) as the 2D channel material.
• Integration of semimetal carbon nanotubes (CNTs) as 1D van der Waals (vdW) contacts to the 2D channel.
• Electrical characterization of the fabricated CNT-VFETs, including on/off ratios, subthreshold swing, and current densities.

Main Results:

• CNT-VFETs with 5-10 nm MoS2 channels achieved high on/off ratios (>10^5) and low subthreshold swing (120-160 mV/dec).
• High current densities exceeding 10^4 A/cm^2 were observed, even with channel thicknesses down to ~3.4 nm.
• Performance improvements are attributed to reduced short channel effects due to CNT contacts' weaker electrostatic screening and tunable barriers.

Conclusions:

• Employing 1D CNT vdW contacts effectively mitigates short channel effects in ultrathin 2D material VFETs.
• CNT-VFETs demonstrate excellent electrical characteristics, enabling operation with sub-5 nm channels.
• These findings highlight the potential of 1D vdW contacts for future ultrascaled transistors in nanoelectronics and nano-optoelectronics.