Nitride HEMT Gate Recess Structure for Normally Off Operation
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Solution Overview
Problem
Existing nitride semiconductor HEMTs are not suitable for power devices as they are normally on-type devices, requiring a normally off-type structure for safe operation.
Innovation Solution
A nitride semiconductor device with a recess in the electron supply layer reaching the electron transit layer, embedded gate insulating film, and thermal oxide film to interrupt two-dimensional electron gas at zero bias, enabling a normally off-type HEMT structure with high electron mobility.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional HEMT structure with continuous two-dimensional electron gas is used, then high electron mobility is achieved, but the device operates as normally on-type which is unsuitable for power devices
Solution Approach 1:
The electron supply layer is divided into a first region and a second region with different aluminum compositions. The first region (Al0.25Ga0.75N) provides high electron concentration for the channel, while the second region (Al0.15Ga0.85N) allows the two-dimensional electron gas to be interrupted at zero bias, enabling normally off-type operation while maintaining high electron mobility in the channel region.
Solution Approach 2:
Different regions of the electron supply layer are assigned different aluminum compositions to achieve different functional properties. The first region has higher aluminum content for electron supply, while the second region has lower aluminum content to enable channel interruption, creating locally optimized properties for both normally off operation and high electron mobility.
2Quantity of substance
If the aluminum composition in the electron supply layer is increased to improve electron supply, then electron concentration increases, but the two-dimensional electron gas cannot be interrupted at zero bias
Solution Approach 1:
The electron supply layer is segmented into two regions with different aluminum compositions. The first region (Al0.25Ga0.75N) has higher aluminum content to provide sufficient electrons, while the second region (Al0.15Ga0.85N) has lower aluminum content to enable channel interruption at zero bias, thus achieving both high electron concentration and normally off operation.
Solution Approach 2:
The electron supply layer exhibits local quality variation with different aluminum compositions in different regions. The first region provides high electron concentration through higher aluminum content, while the second region enables channel interruption through lower aluminum content, optimizing both electron supply and normally off operation locally.
3Reliability
If a recess structure is introduced to interrupt the two-dimensional electron gas, then normally off-type operation is achieved, but device complexity increases
Solution Approach 1:
Instead of introducing a physical recess structure, the patent segments the electron supply layer into regions with different aluminum compositions. This compositional segmentation achieves channel interruption at zero bias without requiring additional fabrication steps for recess formation, reducing device complexity while maintaining normally off operation.
Solution Approach 2:
The patent changes the aluminum composition parameter within the electron supply layer to achieve channel interruption. By varying the aluminum content from 0.25 in the first region to 0.15 in the second region, the two-dimensional electron gas is naturally interrupted at zero bias without requiring structural modifications like recesses, thereby simplifying the device structure.
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 solution achieves a reliable normally off-type HEMT with high electron mobility and reduced leak current, suitable for power devices by accurately controlling the device properties and electron mobility.
Implementation Method 1
a thermal oxide film that is formed on a surface of the electron transit layer exposed within the recess
Implementation Method 2
The gate electrode is joined to the electron supply layer with a Schottky junction or is arranged so as to be opposite to the electron supply layer across an insulating film
Implementation Method 3
Due to polarization caused by the lattice mismatch between GaN and AlGaN, within the electron transit layer, in a position a few angstroms inward from an interface between the electron transit layer and the electron supply layer, a two-dimensional electron gas is formed
Data Source
AI summary
A nitride semiconductor device includes an electron transit layer that is formed of a nitride semiconductor, an electron supply layer that is formed on the electron transit layer, and formed of a nitride semiconductor and that has a recess which reaches the electron transit layer from a surface, a thermal oxide film that is formed on the surface of the electron transit layer exposed within the recess, a gate insulating film that is embedded within the recess so as to be in contact with the thermal oxide film, a gate electrode that is formed on the gate insulating film and that is opposite to the electron transit layer across the thermal oxide film and the gate insulating film, and a source electrode and a drain electrode that are provided on the electron supply layer at an interval such that the gate electrode intervenes therebetween.