U-Shaped Gate Vertical TFET for Sub-60 mV/Decade Switching
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Solution Overview
Problem
Conventional MOSFETs are limited by a sub-threshold swing of about 60 mV/decade at room temperature, making it challenging to achieve faster switching at low operation voltages for future nanometer devices.
Innovation Solution
The development of new vertical tunnel field-effect transistors (TFETs) using III-V compound semiconductor materials, which modulate quantum tunneling through a barrier, allowing for sub-60 mV/decade switching.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional MOSFET drift-diffusion transport mechanism is used, then device structure is simple and easy to manufacture, but sub-threshold swing is limited to about 60 mV/decade at room temperature
Solution Approach 1:
The patent replaces the conventional drift-diffusion transport mechanism with quantum tunneling mechanism. The TFET structure uses band-to-band tunneling through a triangular barrier formed at the source-channel interface, substituting the thermal carrier injection mechanism of MOSFETs with a quantum mechanical tunneling process that is not limited by the 60 mV/decade sub-threshold swing constraint
Solution Approach 2:
The patent employs III-V compound semiconductor materials (such as InGaAs channel with InP source/drain) to create favorable band alignment for efficient band-to-band tunneling. The composite material structure with different bandgaps and effective masses enables enhanced tunneling current while maintaining low off-state leakage, achieving superior sub-threshold swing performance
2Reliability
If quantum tunneling mechanism is used in TFET, then sub-60 mV/decade switching is achieved, but device structure becomes more complex
Solution Approach 1:
The patent segments the channel into distinct regions with different doping profiles and material compositions to create the triangular tunnel barrier. The source region is heavily doped, the channel is lightly doped or intrinsic, and the drain is moderately doped, creating a graded band structure that facilitates efficient tunneling. This segmentation of the channel structure enables controlled quantum tunneling while maintaining manufacturability
Solution Approach 2:
The patent optimizes critical parameters including channel thickness (typically 5-20 nm), source doping concentration (1e19-1e21 atoms/cm³), and material bandgaps to achieve the desired triangular barrier shape. By carefully controlling these parameters during fabrication, the device achieves efficient band-to-band tunneling with sub-60 mV/decade sub-threshold swing while maintaining compatibility with existing semiconductor manufacturing processes
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
The TFETs achieve a large ON state current and a small OFF state leakage current by effectively controlling different tunneling paths for ON and OFF states, overcoming the limitations of conventional MOSFETs.
Implementation Method 1
TFETs switch by modulating quantum tunneling through a barrier. Because of this, TFETs are not limited by the thermal Maxwell-Boltzmann tail of carriers, which limits MOSFET subthreshold swing to about 60 mV/decade of current at room temperature.
Data Source
AI summary
The current disclosure describes a new vertical tunnel field-effect transistor (TFET). The TFET includes a source layer over a substrate. A first channel layer is formed over the source layer. A drain layer is stacked over the first channel layer with a second channel layer stacked therebetween. The drain layer and the second channel layer overlap a first surface portion of the first channel layer. A gate structure is positioned over the channel layer by a second surface portion of the channel layer and contacts a sidewall of the second channel layer.