Tunnel Junction Transistors for Low Voltage Operation
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Solution Overview
Problem
Conventional semiconductor devices face challenges in reducing power supply voltages due to high subthreshold swing and resultant leakage current, limiting further scaling and increasing power dissipation.
Innovation Solution
The development of transistors with a heterojunction structure where the source and channel are made of different materials, optimizing tunneling current through a tunnel junction, allowing for low power supply operation without significant leakage currents, achieved by employing materials like SnO2 and Si or Group III-V semiconductors with tailored band lineups for enhanced tunneling probability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If conventional MOS devices are used, then the subthreshold swing is limited to at best 60 mV/decade, but this results in high leakage current that prevents further power supply voltage scaling
Solution Approach 1:
The patent changes the fundamental parameter of carrier injection mechanism from thermionic emission to quantum mechanical tunneling. By using a highly doped source region (1E19 to 1E21 atoms/cm³) with a thin depletion layer (5nm to 50nm), the device enables direct band-to-band tunneling that is independent of thermal effects, achieving subthreshold swings below 60mV/decade and eliminating the leakage current limitation of conventional MOS devices
Solution Approach 2:
The patent employs a composite structure combining a highly doped source region with a lightly doped channel region. This composite doping profile creates a sharp junction with a thin depletion layer that enables efficient tunneling while maintaining low off-state current. The contrast between the heavily doped source (1E19-1E21 atoms/cm³) and lightly doped channel (1E15-1E18 atoms/cm³) is essential for achieving both low leakage and sub-60mV/decade swing
2Loss of energy
If power supply voltage is reduced to lower power dissipation, then energy consumption decreases, but leakage current increases due to subthreshold swing limitations
Solution Approach 1:
The patent replaces the thermally-driven carrier injection mechanism (thermionic emission) with a quantum mechanical tunneling mechanism. This substitution eliminates the exponential dependence of leakage current on subthreshold swing, allowing the device to maintain low leakage current even at very low power supply voltages (0.3V or lower), thereby reducing both power dissipation and harmful leakage effects simultaneously
3Reliability
If higher doping concentrations are used in the source, then tunneling probability increases, but depletion layer width increases which may reduce tunneling efficiency
Solution Approach 1:
The patent optimizes the doping concentration parameter to achieve the ideal balance: a highly doped source region (1E19 to 1E21 atoms/cm³) that provides sufficient tunneling probability while maintaining a controlled depletion layer width (5nm to 50nm). This precise parameter control ensures that the depletion layer is thin enough for efficient tunneling but not so thin that it causes excessive broadening, achieving optimal tunneling current with the formula J ∝ exp(-4√(2m*)/3ħqE·d)
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
Enables transistors to operate at very low voltage levels (0.3V or lower) with subthreshold swings below 60 mV/decade, reducing power consumption, heat generation, and leakage currents, while maintaining high speed and low threshold voltages, suitable for portable devices and high-density logic circuits.
Implementation Method 1
a tunnel junction formed between the source and the channel, whereby the tunnel junction is configured for injecting carriers from the source to the channel
Data Source
AI summary
The invention provides a transistor having a substrate, a structure supported by the substrate including a source, drain, gate, and channel, wherein the source and the channel are made of different materials, and a tunnel junction formed between the source and the channel, whereby the tunnel junction is configured for injecting carriers from the source to the channel.