Dual-Vt Transistors with Different Gate Stack Materials for HEMT Drivers
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Solution Overview
Problem
In integrated circuits, multi-stage HEMT based drivers face challenges in providing enough over-drive voltage due to threshold voltage (Vt) and forward voltage (Vf) drops across each stage, leading to compromised noise immunity and insufficient over-drive voltage for power switch HEMTs.
Innovation Solution
The use of dual-Vt transistors with different gate stack materials, such as p-type doped GaN, allows for varying threshold voltages, enabling the creation of transistors with different work functions and 2-Dimensional Electron Gas (2-DEG) concentrations, which helps in achieving significant over-drive voltages without compromising noise immunity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If multi-stage E-HEMT based drivers are used to minimize static current, then static current is reduced, but over-drive voltage becomes insufficient due to Vt drops across each stage
Solution Approach 1:
The patent changes the threshold voltage parameter by using different gate stack materials (e.g., TiN, TaN, WN, MoN) with different work functions. This allows creating transistors with different Vt values on the same wafer, enabling the driver stages to have optimized over-drive voltage while maintaining low static current through selective use of enhancement-mode transistors
Solution Approach 2:
The patent applies local quality by allowing different regions of the wafer to have transistors with different gate stack materials and thus different threshold voltages. This enables specific transistor locations to be optimized for specific functions (e.g., higher Vt for noise immunity in certain stages, lower Vt for over-drive in others) while maintaining overall system performance
2Power
If Vt of pull-up E-HEMT transistors is reduced to provide enough over-drive voltage, then over-drive voltage is improved, but noise immunity is compromised
Solution Approach 1:
The patent applies local quality by allowing different regions of the wafer to have transistors with different gate stack materials and thus different threshold voltages. This enables specific transistor locations to be optimized for specific functions (e.g., higher Vt for noise immunity in certain stages, lower Vt for over-drive in others) while maintaining overall system performance
Solution Approach 2:
The patent changes the threshold voltage parameter by using different gate stack materials (e.g., TiN, TaN, WN, MoN) with different work functions. This allows creating transistors with different Vt values on the same wafer, enabling the driver stages to have optimized over-drive voltage while maintaining low static current through selective use of enhancement-mode transistors
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 approach reduces static current and provides sufficient over-drive voltages for drivers while maintaining noise immunity, offering flexibility in transistor design for improved performance and noise resistance.
Implementation Method 1
The use of dual-Vt transistors with different gate stack materials, such as p-type doped GaN, allows for varying threshold voltages, enabling the creation of transistors with different work functions and 2-Dimensional Electron Gas (2-DEG) concentrations
Data Source
AI summary
Apparatus and circuits including transistors with different gate stack materials and methods of fabricating the same are disclosed. In one example, a semiconductor structure is disclosed. The semiconductor structure includes: a substrate; a channel layer formed over the substrate; a first transistor formed over the channel layer, wherein the first transistor comprises a first source region, a first drain region, a first gate structure, and a first polarization modulation portion under the first gate structure; and a second transistor formed over the channel layer, wherein the second transistor comprises a second source region, a second drain region, a second gate structure, and a second polarization modulation portion under the second gate structure, wherein the first polarization modulation portion is made of a material different from that of the second polarization modulation portion.