Oxide Semiconductor Stack for Threshold Voltage Control
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Solution Overview
Problem
Existing semiconductor devices with oxide semiconductors face challenges in achieving a positive threshold voltage for normally-off switching elements and controlling electric characteristics, such as on-state current and field-effect mobility, which are crucial for high-performance and low-power consumption applications.
Innovation Solution
A semiconductor device structure incorporating an oxide semiconductor stack with multiple layers of different energy gaps and a mixed region between them, where the energy gap of the mixed region is between those of the stacked layers, is used to improve field-effect mobility and reduce off-state current, allowing for precise control of electric characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If oxide semiconductor materials are used to improve field-effect mobility and on-state current, then on-state characteristics are improved, but controlling the threshold voltage to be positive becomes difficult
Solution Approach 1:
The semiconductor layer is divided into multiple oxide semiconductor layers with different energy gaps. The first oxide semiconductor layer has a larger energy gap for better off-state characteristics, while the second oxide semiconductor layer has a smaller energy gap for better on-state characteristics. This segmentation allows independent optimization of different transistor states.
Solution Approach 2:
Different regions of the semiconductor layer are assigned different energy gap characteristics. The first oxide semiconductor layer (closer to the gate electrode) provides local quality for threshold voltage control and off-state performance, while the second oxide semiconductor layer provides local quality for on-state current and field-effect mobility enhancement.
2Speed
If oxide semiconductor layers with different energy gaps are stacked to improve electric characteristics, then field-effect mobility and on-state current are improved, but device structure becomes more complex
Solution Approach 1:
The solution transitions from a single-layer structure to a multi-layer stacked structure, adding the dimension of vertical layering. This allows different oxide semiconductor materials with complementary characteristics to be combined, achieving superior on-state current while maintaining manageable structural complexity through systematic layer arrangement.
3Ease of manufacture
If a single oxide semiconductor layer is used to simplify the structure, then manufacturing is easier, but precise control of electric characteristics is not achieved
Solution Approach 1:
The invention uses a composite structure of multiple oxide semiconductor layers with different energy gaps. This composite approach combines the advantages of materials with large energy gaps (good off-state characteristics) and materials with small energy gaps (good on-state characteristics), achieving precise control of electric characteristics that cannot be obtained with a single material.
Data Source
AI summary
To provide a transistor including an oxide semiconductor layer and having electric characteristics required depending on an intended use and provide a semiconductor device including the transistor, in a transistor in which a semiconductor layer, source and drain electrode layers, a gate insulating film, and a gate electrode are stacked in this order over an oxide semiconductor insulating film, an oxide semiconductor stack layer which includes at least two oxide semiconductor layers with energy gaps different from each other and a mixed region therebetween is used as the semiconductor layer.