Fin Structure TFET with Epitaxial SiGe Source and Silicon Drain
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Solution Overview
Problem
Conventional tunneling field effect transistors (TFETs) face limitations in achieving improved drive current capabilities.
Innovation Solution
The TFET device is enhanced by forming a fin of semiconductor material with an epitaxial germanium content source region doped with a first conductivity type and an epitaxial silicon content drain region doped with a second conductivity type, along with a gate electrode straddling the channel region and sidewall spacers, to facilitate better tunneling current and reduced tunneling barrier width.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional TFET structure with uniformly doped source and drain regions is used, then manufacturing process is simple, but drive current capability is limited
Solution Approach 1:
The patent applies local quality by creating distinct epitaxial source and drain regions with different semiconductor group IV materials (e.g., SiGe source region and Si drain region) and different doping concentrations. This local differentiation optimizes tunneling characteristics at the source region while maintaining proper carrier collection at the drain, thereby improving drive current capability without uniformly complicating the entire device structure.
Solution Approach 2:
The patent changes material composition parameters by introducing germanium content variations in the source region (e.g., Si1-xGex where x>0) compared to the drain region. This parameter change modifies the band structure and tunneling barrier characteristics, enabling enhanced tunneling current and improved drive current capability while maintaining device functionality.
2Reliability
If germanium content source region is used to improve tunneling current, then tunneling efficiency increases, but manufacturing precision requirements increase
Solution Approach 1:
The patent applies preliminary action by forming the epitaxial source and drain regions with predetermined material compositions and doping concentrations during the epitaxial growth process itself, rather than attempting to modify these properties later. This upfront definition of material properties during growth ensures consistent tunneling efficiency while managing manufacturing precision through controlled deposition parameters.
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 configuration significantly improves drive current capabilities by reducing tunneling barrier width and enhancing active dopant concentration, leading to better tunneling efficiency and reduced contact resistance.
Implementation Method 1
This leads to band-to-band tunneling (BTBT) of electrons (reference 24) from the valence band of the source region 14 to the conduction band of the drain region 16
Implementation Method 2
the applied gate voltage induces sufficient band bending to produce a reduction of the tunneling barrier width
Implementation Method 3
The increase in the valence band gap (Ev) resulting from the use of a germanium source region 14 further decreases/narrows the tunneling barrier width
Data Source
AI summary
A tunneling field effect transistor is formed from a fin of semiconductor material on a support substrate. The fin of semiconductor material includes a source region, a drain region and a channel region between the source region and drain region. A gate electrode straddles over the fin at the channel region. Sidewall spacers are provided on each side of the gate electrode. The source of the transistor is made from an epitaxial germanium content source region grown from the source region of the fin and doped with a first conductivity type. The drain of the transistor is made from an epitaxial silicon content drain region grown from the drain region of the fin and doped with a second conductivity type.