Nitride Semiconductor Transistor with Composition Gradient
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Solution Overview
Problem
It is challenging to create field-effect transistors with nitride semiconductor layers that are normally-off type and have high threshold voltages, as existing configurations struggle to achieve the necessary high withstand voltages and low resistivities.
Innovation Solution
The semiconductor device incorporates a second nitride semiconductor layer formed by stacking layers with different compositions, polarized in a specific direction to create a higher negative charge density under the gate electrode, and an AlxGa1-xN or AlxIn1-xN first layer, with an Al yGa1-yN or Al yIn1-yN second layer, where the Al composition increases towards the first layer, ensuring a high threshold voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a field-effect transistor uses two-dimensional electron gas at the AlGaN/GaN hetero junction interface as carriers, then low resistivity is achieved, but it becomes difficult to make the transistor normally-off type with high threshold voltage
Solution Approach 1:
The patent divides the channel layer into multiple AlGaN layers with different Al compositions stacked in sequence. This segmentation allows independent control of electron gas generation at each interface while creating an overall negative charge distribution that raises the threshold voltage, enabling normally-off operation without sacrificing low resistivity.
Solution Approach 2:
Different regions of the channel layer are assigned different Al compositions to achieve different local functions: lower Al composition regions generate electron gas for low resistivity, while higher Al composition regions create negative charge for high threshold voltage. This local quality differentiation resolves the contradiction between normally-off characteristic and ease of manufacture.
2Ease of manufacture
If the second nitride semiconductor layer is formed by stacking plural semiconductor layers with different compositions, then high threshold voltage is achieved through increased negative charge density, but device structure becomes more complex
Solution Approach 1:
The patent changes the composition parameter (Al concentration) of the nitride semiconductor layers to control the polarization state. By adjusting Al composition in the stacked layers, the negative charge density at interfaces is controlled, thereby achieving high threshold voltage. This parameter change approach simplifies the manufacturing process compared to other methods.
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 results in a field-effect transistor with a high threshold voltage, improved withstand voltage, and low resistivity, effectively addressing the challenges of creating normally-off transistors with nitride semiconductor layers.
Implementation Method 1
the semiconductor layers are polarized in the same direction at least in the region under the gate electrode, and have compositions different from each other, with the result that the amount of negative charge is larger than that of positive charge at each interface between two semiconductor layers
Data Source
AI summary
A semiconductor device includes a first semiconductor layer, a second semiconductor layer formed over the first semiconductor layer, a gate insulating film contacting the second semiconductor layer, and a gate electrode facing the second semiconductor layer via the gate insulating film. The first semiconductor layer includes an Alxα1-xN layer (α includes Ga or In, and 0<x<1), and the second semiconductor layer includes an Alyα1-yN layer (0≦y<1), in which y of the Alyα1-yN layer forming the second semiconductor layer increases at least in a region under the gate electrode as a position where y is measured approaches the first semiconductor layer.