Depletion-Mode Current Source for GaN Start-Up Circuits
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Solution Overview
Problem
Existing semiconductor fabrication processes for GaN FETs face challenges in integrating depletion-mode transistors without modifying the enhancement-mode process, leading to increased costs and complexity, especially in high-voltage start-up circuits for applications like AC-to-DC power converters.
Innovation Solution
A depletion-mode current source is fabricated using a conductive electrode over a 2DEG or 2DHG channel, allowing for high-voltage operation without requiring additional masks or materials, enabling integration within an enhancement-mode GaN process flow.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If depletion-mode transistors are integrated using separate fabrication processes, then depletion-mode functionality is achieved, but manufacturing complexity and cost increase
Solution Approach 1:
The patent merges depletion-mode and enhancement-mode transistor fabrication into a single unified process. The same AlGaN/GaN heterostructure and metal organic chemical vapor deposition (MOCVD) process are used to create both depletion-mode devices (with continuous 2DEG channels) and enhancement-mode devices (with interrupted channels), eliminating the need for separate fabrication lines and reducing manufacturing complexity
Solution Approach 2:
The fabrication process is designed to be universal, capable of producing both depletion-mode and enhancement-mode transistors using identical steps. The process can selectively create different channel configurations (continuous for depletion-mode, interrupted for enhancement-mode) within the same wafer, allowing multi-functionality and reducing overall device complexity
2Adaptability or versatility
If depletion-mode transistors are integrated using separate fabrication processes, then depletion-mode functionality is achieved, but production cost increases
Solution Approach 1:
By combining depletion-mode and enhancement-mode transistor fabrication into a single process flow using the same MOCVD equipment and materials, the patent eliminates the need for separate production lines. This merging of processes reduces capital equipment requirements, simplifies manufacturing logistics, and lowers overall production costs while maintaining depletion-mode functionality
Solution Approach 2:
The patent uses homogeneous fabrication methods (same AlGaN/GaN materials, same MOCVD process conditions, same device structures) for both depletion-mode and enhancement-mode transistors. This homogeneity in manufacturing approach simplifies process control, reduces variability, and lowers production costs compared to using disparate fabrication techniques
3Strength
If conductive electrode extends over 2DEG channel, then high-voltage capability is achieved, but device area increases
Solution Approach 1:
The patent addresses the voltage breakdown problem by moving the protective structure from a planar configuration to a three-dimensional configuration. The conductive electrode is positioned above the 2DEG channel at a vertical distance, creating a capacitive structure that provides high-voltage capability without requiring excessive lateral area. This dimensional transition allows voltage stress to be managed in the vertical dimension rather than consuming horizontal device area
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 allows for the creation of a high-voltage depletion-mode current source that can be integrated with enhancement-mode FETs on the same die, reducing production costs and complexity while maintaining high-voltage capabilities, suitable for start-up circuits in power converters.
Implementation Method 1
A current source includes a two-dimensional electron gas (2DEG) or two-dimensional hole gas (2DHG) channel coupled between a first terminal of the depletion-mode current source and a second terminal of the depletion-mode current source
Implementation Method 2
A conductive electrode coupled to the first terminal is above and extends over at least a portion of the 2DEG or 2DHG channel
Data Source
AI summary
A depletion-mode current source having a saturation current of sufficient accuracy for use as a pre-charge circuit in a start-up circuit of an AC-to-DC power converter is fabricated using an enhancement-mode-only process. The depletion-mode current source can be fabricated on the same integrated circuit (IC) as a gallium nitride field-effect transistor (FET) and resistive and capacitive components used in the start-up circuit, without affecting the enhancement-mode-only fabrication process by requiring additional masks or materials, as would be required to fabricate a depletion-mode FET on the same IC as an enhancement-mode FET. The current source includes a resistive patterned two-dimensional electron gas (2DEG) or two-dimensional hole gas (2DHG) channel coupled between two terminals and one or more metal field plates extending from one of the terminals and overlying the patterned area of the channel, the field plates being separated from the channel and from each other by dielectric layers.