GaN HEMT AlGaN Layer Segmentation for Normally-Off Operation
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Solution Overview
Problem
Existing semiconductor devices with heterojunction structures face challenges in controlling two-dimensional electron gas (2DEG) density, leading to instability in blocking breakdown voltage and on resistance, particularly in achieving a normally-off device configuration.
Innovation Solution
A semiconductor device with a lateral HEMT structure featuring a GaN/AlGaN heterojunction, where the AlGaN layer includes a first AlGaN layer with a higher Al mixed crystal ratio and a second AlGaN layer with a lower Al mixed crystal ratio, strategically positioned to induce negative fixed charge, reducing 2DEG formation under the gate and optimizing AlGaN layer thickness to control 2DEG density.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the AlGaN electron supply layer thickness is reduced to reduce stress and suppress piezoelectric polarization, then blocking breakdown voltage is improved, but 2DEG density control becomes unstable
Solution Approach 1:
The AlGaN electron supply layer is divided into multiple AlGaN layers with different Al mixed crystal ratios. The first AlGaN layer has a higher Al mixed crystal ratio (0.2-0.35) to reduce stress and piezoelectric polarization, while the second AlGaN layer has a lower Al mixed crystal ratio (0.05-0.2) to maintain stable 2DEG density. This segmentation allows simultaneous optimization of both blocking breakdown voltage and 2DEG density stability.
Solution Approach 2:
Different regions of the AlGaN electron supply layer are assigned different Al mixed crystal ratios to achieve different local functions. The first AlGaN layer (higher Al ratio) is optimized for stress reduction and piezoelectric polarization suppression, while the second AlGaN layer (lower Al ratio) is optimized for stable 2DEG density. This local quality differentiation resolves the contradiction between improving blocking breakdown voltage and maintaining 2DEG density stability.
2Ease of operation
If the AlGaN layer structure is modified to control 2DEG density, then device operation mode can be changed to normally-off, but on resistance increases
Solution Approach 1:
The Al mixed crystal ratio parameter is changed across different AlGaN layers to achieve different electrical characteristics. By precisely controlling the Al mixed crystal ratios (first layer: 0.2-0.35, second layer: 0.05-0.2) and thicknesses, the patent achieves normally-off operation while minimizing on resistance increase. The parameter optimization balances the trade-off between device operation mode and on resistance.
3Ease of manufacture
If a single AlGaN layer is used, then manufacturing is simple, but blocking breakdown voltage becomes unstable
Solution Approach 1:
The AlGaN electron supply layer is segmented into multiple layers with different Al mixed crystal ratios to achieve stable blocking breakdown voltage. While this increases structural complexity compared to a single layer, the segmentation enables precise control of stress distribution and piezoelectric polarization, resulting in stable blocking breakdown voltage that outweighs the manufacturing complexity increase.
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 configuration enables improved control over blocking breakdown voltage and on resistance, allowing for the creation of a normally-off device by reducing 2DEG density and suppressing degradation, while minimizing on resistance increase.
Implementation Method 1
two-dimensional electron gas (hereinafter referred to as the 2 DEG) carrier is induced, by a piezoelectric effect and a spontaneous polarization effect, below the AlGaN electron supply layer
Implementation Method 2
two-dimensional electron gas (hereinafter referred to as the 2 DEG) carrier is induced, by a piezoelectric effect and a spontaneous polarization effect, below the AlGaN electron supply layer
Implementation Method 3
A current flows between the source and the drain through the 2 DEG carrier and a channel portion provided by a surface layer portion of the GaN electron transit layer under the gate electrode
Data Source
AI summary
A semiconductor device includes a lateral switching device having: a substrate; a channel forming layer that has a heterojunction structure made of a GaN layer and an AlGaN layer and is formed with a recessed portion, on the substrate; a gate structure part that includes a gate insulating film and a gate electrode formed in the recessed portion; and a source electrode and a drain electrode on opposite sides of the gate structure part on the channel forming layer. The AlGaN layer includes a first AlGaN layer that has an Al mixed crystal ratio determining a two dimensional electron gas density, and a second AlGaN layer that has an Al mixed crystal ratio smaller than that of the first AlGaN layer to induce negative fixed charge, and is disposed in contact with the gate structure part and spaced from the source electrode and the drain electrode.