Nitride Semiconductor Device With Ridge-Shaped Gate For Leakage Reduction
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Solution Overview
Problem
Nitride semiconductor devices with ridge-shaped p-type GaN gate layers experience high gate leakage currents and threshold voltage fluctuations, leading to inefficiencies and heat generation issues in high-frequency switching applications.
Innovation Solution
A nitride semiconductor device configuration with a ridge-shaped gate portion including a nitride semiconductor gate layer with acceptor-type impurities, a gate metal film, and a gate insulating film that reduces gate leakage current and stabilizes threshold voltage by forming an interface level that pins the barrier height, rather than an interface for electron entry and exit.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a ridge-shaped p-type GaN gate layer is used to achieve normally-off operation, then the device can be controlled to turn off, but gate leakage current increases
Solution Approach 1:
An AlGaN barrier layer is introduced as an intermediary between the p-type GaN gate layer and the AlGaN electron supply layer. This barrier layer has a wider bandgap and higher electron affinity, creating a potential barrier that blocks electron leakage from the gate to the source, while still allowing the p-type gate to deplete the channel for normally-off operation.
Solution Approach 2:
The gate structure uses a composite of multiple nitride semiconductor layers with different compositions and properties: p-type GaN for hole injection and channel depletion, AlGaN barrier layer for electron blocking, and AlGaN electron supply layer for 2DEG formation. This composite structure achieves both normally-off control and low gate leakage.
2Loss of energy
If a gate insulating film is formed on the nitride semiconductor gate layer to reduce gate leakage current, then gate leakage is reduced, but threshold voltage fluctuates
Solution Approach 1:
The AlGaN barrier layer serves as an intermediary that eliminates the need for a gate insulating film. It provides electrical isolation and electron blocking functionality without creating interface traps, thereby maintaining stable threshold voltage while reducing gate leakage current.
Solution Approach 2:
By changing the material parameter (using AlGaN barrier layer instead of insulating film), the interface quality is improved. The AlGaN-AlGaN interface has fewer traps and defects compared to semiconductor-insulator interfaces, resulting in stable threshold voltage while achieving low gate leakage.
3Device complexity
If the gate structure is simplified to reduce complexity, then manufacturing is easier, but gate leakage current increases
Solution Approach 1:
The gate structure uses a composite of nitride semiconductor layers that can be grown in-situ by MOCVD, avoiding the need for separate insulating film deposition and patterning processes. This composite approach reduces manufacturing complexity while achieving low gate leakage through the inherent electron-blocking properties of the AlGaN barrier layer.
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 configuration effectively reduces gate leakage current and suppresses threshold voltage fluctuations, enhancing the reliability and efficiency of nitride semiconductor devices, particularly in high-frequency switching applications.
Implementation Method 1
due to polarization caused by lattice mismatch between GaN and AlGaN, a two-dimensional electron gas is formed at a position several A inward from an interface between the electron transit layer and the electron supply layer
Implementation Method 2
an interface level at which electrons enter and exit is formed at an interface between the nitride semiconductor gate layer and the gate insulating film, a threshold voltage may fluctuate
Data Source
AI summary
A nitride semiconductor device includes: a first nitride semiconductor layer constituting an electron transit layer; a second nitride semiconductor layer formed on the first nitride semiconductor layer and constituting an electron supply layer; a ridge-shaped gate portion formed on the second nitride semiconductor layer; and a source electrode and a drain electrode disposed on the second nitride semiconductor layer so as to face each other with the ridge-shaped gate portion interposed therebetween, wherein the ridge-shaped gate portion includes: a nitride semiconductor gate layer containing acceptor-type impurities and disposed on the second nitride semiconductor layer; a gate metal film disposed on the nitride semiconductor gate layer; a gate insulating film formed on the gate metal film; and a gate electrode capacitively-coupled to the gate metal film by the gate insulating film.