Compact-Drain Heterostructure TFET for Low Ambipolar Current
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Solution Overview
Problem
Tunnel field-effect transistors (TFETs) face limitations in achieving high on-current and suppressing ambipolar current, making it difficult to replace metal-oxide-semiconductor field-effect transistors (MOSFETs) due to complex processing challenges.
Innovation Solution
A transistor design featuring a compact drain, doping-less, and hetero-material structure with a silicon-germanium channel and germanium source, utilizing specific electrode materials and work functions to optimize ambipolar and on-current characteristics, allowing for a simple fabrication process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If tunneling mechanism is used to achieve low subthreshold swing, then power characteristics are improved, but on-current is limited
Solution Approach 1:
The patent applies different materials with different band gaps to different regions: SiGe channel for low effective mass and high mobility, Ge source for high tunneling probability, and Si drain for stable band alignment. This local optimization of material properties in each region simultaneously enhances tunneling efficiency for low power while maintaining high on-current through improved carrier transport.
Solution Approach 2:
The invention uses a composite heterostructure combining Si, SiGe, and Ge materials. The SiGe channel layer provides high mobility, the Ge source layer enables efficient hole injection through band alignment, and the Si drain ensures stable energy band configuration. This composite material approach resolves the contradiction by leveraging the complementary strengths of different semiconductor materials.
2Reliability
If hetero-material structure is used to improve on-current, then manufacturing complexity increases
Solution Approach 1:
The patent employs selective epitaxial growth to pre-form the SiGe channel and Ge source layers with precise thickness and composition control before any doping or device fabrication steps. This preliminary formation of the heterostructure with optimized band alignment eliminates the need for complex post-growth doping processes, reducing overall manufacturing complexity while maintaining high on-current characteristics.
Solution Approach 2:
The invention extracts and eliminates the traditional doping process from the fabrication flow by relying on the built-in band alignment of the heterostructure for carrier injection. This removal of the doping step simplifies the manufacturing process significantly while maintaining the ability to control on-current through the material composition and thickness parameters.
3Object-generated harmful factors
If compact drain structure is used to reduce ambipolar current, then device performance is improved, but manufacturing precision requirements increase
Solution Approach 1:
The patent controls ambipolar current by precisely adjusting the thickness parameter of the Si drain layer and the composition parameter of the SiGe channel layer. By optimizing these parameters during epitaxial growth, the energy band alignment is tuned to suppress band-to-band tunneling in reverse bias while maintaining high forward current, thereby reducing ambipolar current without requiring extreme manufacturing precision.
Solution Approach 2:
The compact Si drain structure is designed with specific thickness and material composition tailored to create a potential barrier that selectively blocks ambipolar current. The local optimization of the drain region's material properties and dimensions provides ambipolar suppression while the overall fabrication process remains within standard precision capabilities through controlled epitaxial growth.
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 design effectively reduces ambipolar current and increases on-current, enabling mass production at low unit cost while avoiding the complexities of traditional doping processes.
Implementation Method 1
since current is induced in TFETs through the quantum tunneling phenomenon between the valence band and the conduction band for each region
Data Source
AI summary
The present invention relates to a transistor based on a compact drain and hetero-material structure. The transistor according to one embodiment includes substrates including a buried oxide (BOX) layer and active layers formed on the buried oxide layer; an insulating layer formed on the substrates; and electrode layers formed on the insulating layer and including a drain electrode, a gate electrode, and a source electrode. The active layers include a first semiconductor layer corresponding to a drain region, a second semiconductor layer corresponding to a channel region, and a third semiconductor layer corresponding to a source region. The first semiconductor layer is formed to be thinner than the second semiconductor layer, and the third semiconductor layer is formed of a material having a band gap lower than that of the second semiconductor layer.