P-TFET Source Doping Profile for Low Subthreshold Swing
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Solution Overview
Problem
Current tunnel field-effect transistors (TFETs), particularly p-type TFETs, face challenges in achieving low subthreshold swing and high on-current due to high doping levels leading to source degeneration and increased leakage currents, while also being difficult to fabricate with low defect densities.
Innovation Solution
A p-type TFET design featuring a source region with a lowly doped section and a highly doped section, where the lowly doped section is at least 10 nm long and has a doping level below 5×10^18 at/cm^3, and the highly doped section is between 1 monolayer and 20 nm long with a doping level above 5×10^18 at/cm^3, allowing for reduced doping degeneracy and increased electric field for improved tunneling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If high doping levels are used in the source region to increase on-current, then tunneling efficiency improves, but source degeneration occurs and subthreshold swing increases
Solution Approach 1:
The source region is divided into two zones with different doping levels: a lightly-doped bulk region (10^16-10^18 atoms/cm³) and a highly-doped tunneling region (10^19-10^21 atoms/cm³) at the source-channel interface. This local differentiation allows the bulk to maintain low degeneracy for good subthreshold swing while the interface provides high doping for efficient tunneling and high on-current.
2Object-generated harmful factors
If high doping levels are used to reduce leakage currents, then off-state performance improves, but source degeneration increases and fabricability decreases
Solution Approach 1:
High doping is applied locally only at the source-channel interface region where it is most effective for reducing leakage and enhancing tunneling, while the bulk source region remains lightly-doped. This localized approach minimizes the total amount of dopant required, simplifying fabrication processes and reducing defects compared to uniform high-doping approaches.
3Power
If uniform high doping is applied to the source region, then on-current increases, but defect density increases and fabricability decreases
Solution Approach 1:
The doping profile transitions from uniform high doping to a spatially varying profile with low doping in the bulk and high doping at the interface. This reduces the total dopant volume, minimizing precipitation and clustering defects, while still achieving the necessary tunneling efficiency at the critical interface region for high on-current.
Solution Approach 2:
The source region is segmented into distinct doping zones that can be formed using separate processing steps or graded doping approaches, allowing better control over dopant distribution and reducing fabrication-induced defects compared to uniform doping.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This design achieves a low subthreshold swing and high on-current, reducing doping degeneracy and maintaining a steep subthreshold swing, while being easier to fabricate with fewer defects, thus improving the performance of p-TFETs to match or exceed that of n-TFETs.
Implementation Method 1
Reaching sub-60 mV/dec SS is possible thanks to the TFET's working principle, which is based on band-to-band tunneling (BTBT), instead of on drift and diffusion like a MOSFET.
Implementation Method 2
The counterdoped pocket increases the electric field at the tunnel junction, resulting in more efficient tunneling and hence a larger on-current
Data Source
AI summary
A p-type Tunnel Field-Effect Transistor comprises a drain p-type semiconductor region, a source n-type semiconductor region, and at least one gate stack. The source n-type semiconductor region comprises a lowly doped section with a length of at least 10 nm and with a doping level of n-type dopant elements below 5×1018 at/cm3 and, in contact with the lowly doped section, a highly doped section with a length between 1 monolayer and 20 nm and with a doping level of n-type dopant elements above 5×1018 at/cm3.