p-GaN Ridge Structure for Higher Gate Withstand Voltage
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Solution Overview
Problem
The existing nitride semiconductor devices with a p type GaN layer of a ridge shape face issues with low maximum gate voltage rating due to electron leakage and current collapse, primarily caused by band bending and increased trap levels resulting from dry etching, which also lead to a shortened distance between the etched surface and the two-dimensional electron gas.
Innovation Solution
A nitride semiconductor device is designed with a first nitride semiconductor layer as an electron transit layer, a second nitride semiconductor layer with a higher bandgap as an electron supply layer, and a third nitride semiconductor layer with a ridge portion containing an acceptor-type impurity. The device includes a gate electrode, passivation film, and electrodes with extension portions that extend outward from the ridge portion, reducing electron leakage and current collapse by increasing the gate withstand voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a p type GaN layer of ridge shape is used to achieve normally-off operation, then the device can be made normally-off type, but the gate withstand voltage is limited due to electron leakage and current collapse
Solution Approach 1:
The patent applies local quality by creating an extension portion only in specific regions (between the ridge portion side end of the first opening portion and the first opening portion end of the ridge portion, and/or between the ridge portion side end of the drain electrode and the second opening portion end of the ridge portion) rather than uniformly across the entire structure. This localized modification increases the distance to the two-dimensional electron gas precisely where needed to suppress current collapse and electron leakage, while maintaining the normally-off operation capability through the p type GaN layer ridge portion.
2Ease of manufacture
If dry etching is used to form the p type GaN layer ridge shape, then the structure can be formed, but trap levels increase and the distance to the two-dimensional electron gas shortens
Solution Approach 1:
The patent extracts the harmful effect of dry etching by removing the etched surface from the critical region near the two-dimensional electron gas. The extension portion protrudes into the first opening portion and second opening portion, creating a physical barrier that increases the distance between the etched surface and the two-dimensional electron gas, thereby extracting the source of trap levels and current collapse from the device operation.
3Manufacturing precision
If the etching stops at intermediate thickness of the AlGaN electron supply layer, then the ridge shape is formed, but the distance between the etched surface and the two-dimensional electron gas is shortened
Solution Approach 1:
The patent applies dimensionality change by creating an extension portion that protrudes horizontally into the first opening portion and second opening portion, rather than only varying the vertical thickness. This lateral extension increases the distance to the two-dimensional electron gas in the horizontal dimension, compensating for the intermediate etching depth needed to form the ridge shape, thereby maintaining manufacturing precision while improving reliability.
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
The proposed design enhances gate withstand voltage and suppresses current collapse by increasing the distance between the etched surface and the two-dimensional electron gas, thereby improving the device's operational efficiency and reliability.
Implementation Method 1
a channel is eliminated by a depletion layer spreading from the p type GaN gate layer to achieve a normally-off operation
Implementation Method 2
Due to polarization caused by lattice mismatch of GaN and AlGaN, a two-dimensional electron gas (2DEG) is formed at a position inside the electron transit layer
Data Source
AI summary
A nitride semiconductor device includes a source electrode that is in contact with a second nitride semiconductor layer via a first opening portion and with which a portion is formed above a passivation film and a drain electrode that is in contact with the second nitride semiconductor layer via a second opening portion and with which a portion is formed above the passivation film such as to oppose the source electrode across a ridge portion, and the third nitride semiconductor layer has, between a ridge portion side end of the first opening portion and a first opening portion end of the ridge portion and/or between a ridge portion side end of the drain electrode and a second opening portion end of the ridge portion, an extension portion that extends outward from a portion below a thickness intermediate position of at least one side surface of the ridge portion.