Double-Gate Carbon Nanotube Transistor for Short-Channel Control
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Solution Overview
Problem
The semiconductor industry faces challenges in transistor scaling due to unwanted short channel effects such as drain-induced barrier lowering and large subthreshold swing, which are exacerbated by the reduction in transistor size, and traditional 3D bulk crystal channel materials suffer from carrier scattering and threshold voltage variations.
Innovation Solution
A double-gate carbon nanotube transistor is developed, where carbon nanotubes are formed over a dielectric layer, a dummy gate is removed, and a gate dielectric is formed to encircle the nanotubes, reducing short-channel effects by suspending the nanotubes and creating a double-gate structure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If transistor size is reduced to increase density, then productivity is improved, but short channel effects worsen
Solution Approach 1:
The patent transitions from planar 2D gating to 3D wrap-around gating, where the gate electrode surrounds the carbon nanotube channel in multiple dimensions. This dimensional change provides superior electrostatic control over the channel, effectively suppressing short channel effects while maintaining scaled dimensions for high density.
Solution Approach 2:
The patent employs carbon nanotubes as the channel material, utilizing their unique one-dimensional crystal structure with superior carrier mobility and electrostatic control compared to traditional bulk semiconductor materials. This composite approach combines the advantages of nanoscale confinement with high-quality material properties.
2Reliability
If channel body thickness is reduced to mitigate short channel effects, then reliability is improved, but manufacturing precision worsens
Solution Approach 1:
The patent changes the fundamental parameter of channel geometry from bulk 3D structure to one-dimensional nanotube structure. This parameter change eliminates the need for precise thickness control while maintaining excellent electrostatic control and suppressing short channel effects through the inherent properties of carbon nanotubes.
3Ease of manufacture
If 3D bulk crystal channel materials are used, then ease of manufacture is improved, but reliability worsens due to carrier scattering
Solution Approach 1:
The patent uses carbon nanotubes with their unique one-dimensional crystal structure that inherently provides superior carrier mobility by eliminating bulk scattering mechanisms. The nanotube structure maintains crystalline quality while providing superior electrical transport properties compared to bulk materials.
4Reliability
If body thickness is reduced to improve short channel control, then reliability is improved, but device complexity worsens due to threshold voltage variations
Solution Approach 1:
The patent changes the channel from bulk structure to one-dimensional nanotubes, which provides natural immunity to threshold voltage variations. The quantized energy levels and superior electrostatic control in nanotubes eliminate the sensitivity to dimensional variations that plagues bulk-based devices.
Data Source
AI summary
A method includes depositing a dielectric layer over a substrate, forming carbon nanotubes on the dielectric layer, forming a dummy gate stack on the carbon nanotubes, forming gate spacers on opposing sides of the dummy gate stack, and removing the dummy gate stack to form a trench between the gate spacers. The carbon nanotubes are exposed to the trench. The method further includes etching a portion of the dielectric layer underlying the carbon nanotubes, with the carbon nanotubes being suspended, forming a replacement gate dielectric surrounding the carbon nanotubes, and forming a gate electrode surrounding the replacement gate dielectric.