Ga2O3 Field-Effect Transistor Threshold Shift for Normally-Off Operation
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Solution Overview
Problem
Conventional Ga2O3-based field-effect transistors operate in a normally-on state, making them unsuitable for high-temperature and radiation exposure environments, and they lack the desired gate threshold voltage for safe and versatile power device applications.
Innovation Solution
A field-effect transistor design incorporating a Ga2O3-based semiconductor layer with a source and drain region, a gate electrode separated by a gate insulating film, and an interface charge forming a negative charge, allowing for control of the gate threshold voltage through the thickness and relative permittivity of the gate insulating film, achieving a threshold voltage of at least 4.5V.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a gate insulating film is provided at the interface between gate metal and Ga2O3-based semiconductor layer, then the transistor operates in normally-on state, but normally-off operation is required for safety and replacement of Si/SiC power devices
Solution Approach 1:
The patent applies parameter changes by introducing interface charge (negative charge) at the gate insulating film/semiconductor interface and adjusting the gate insulating film thickness to shift the gate threshold voltage to a positive value (≥4.5V), thereby achieving normally-off operation while maintaining reliability in harsh environments
2Adaptability or versatility
If the gate threshold voltage is not adjusted, then the transistor may malfunction, but achieving a gate threshold voltage of at least 4.5V is required to match existing power devices and enhance versatility
Solution Approach 1:
The patent changes physical parameters including gate insulating film thickness (5-140 nm) and interface charge density to achieve a gate threshold voltage of at least 4.5V, matching existing Si/SiC power devices and enhancing versatility for power device applications
Solution Approach 2:
The gate insulating film acts as an intermediary layer that, combined with interface charge, enables precise control of the gate threshold voltage to achieve the desired 4.5V threshold for versatile power device applications
3Ease of manufacture
If conventional depletion-mode MOSFET structure is used, then the transistor can be fabricated with Ga2O3-based semiconductor, but the transistor cannot achieve normally-off operation required for high-temperature and radiation exposure environments
Solution Approach 1:
The patent modifies the conventional depletion-mode structure by introducing interface charge and optimizing gate insulating film parameters to achieve normally-off operation, enabling reliable performance in high-temperature and radiation exposure environments while maintaining ease of fabrication
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 normally-off operation and enhances the versatility of Ga2O3-based field-effect transistors for use in harsh environments, matching the gate threshold voltage of existing Si or SiC power devices for improved safety and performance.
Implementation Method 1
a gate threshold voltage is not less than 4.5V... determined taking into consideration at least the interface charge and a thickness and a relative permittivity of the gate insulating film
Implementation Method 2
an interface charge comprising a negative charge is formed between the gate electrode and the channel region
Data Source
AI summary
A field-effect transistor includes a Ga2O3-based semiconductor layer, a source region and a drain region that are formed inside the Ga2O3-based semiconductor layer, a gate electrode that is formed, via a gate insulating film, on a channel region as the Ga2O3-based semiconductor layer between the source region and the drain region, a source electrode connected to the source region, and a drain electrode connected to the drain region. An interface charge including a negative charge is formed between the gate electrode and the channel region, and a gate threshold voltage is not less than 4.5V.