Oxide Semiconductor Transistor Structure for Stable Threshold Voltage
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Solution Overview
Problem
Existing thin film transistors using oxide semiconductors face challenges in maintaining stable electric characteristics due to variations in composition and manufacturing conditions, leading to fluctuating defect levels and electric characteristics.
Innovation Solution
A transistor structure is developed with an oxide semiconductor layer comprising a first region with a higher carrier concentration and a second region with a lower carrier concentration, separated by an energy barrier to prevent carrier trapping and stabilize the threshold voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If an oxide semiconductor film is used as the channel layer, then field effect mobility is improved and crystallization steps are eliminated, but the composition varies with manufacturing conditions causing electric characteristics to fluctuate
Solution Approach 1:
The oxide semiconductor layer is divided into three distinct regions: a first region with high carrier concentration, a second region with low carrier concentration serving as the channel, and a third region with intermediate carrier concentration. This segmentation isolates the channel region from the influence of manufacturing condition variations, maintaining stable electric characteristics while preserving high mobility in the source/drain regions.
Solution Approach 2:
Different regions of the oxide semiconductor layer are assigned different carrier concentrations tailored to their specific functions: the first region has high carrier concentration for efficient charge injection, the second region has low carrier concentration for stable threshold voltage, and the third region has intermediate concentration for transition. This local optimization resolves the contradiction between mobility and stability.
2Power
If the carrier concentration in the oxide semiconductor layer is increased to improve field effect mobility, then on-current increases, but off-current also increases reducing the on/off ratio
Solution Approach 1:
The oxide semiconductor layer is segmented into regions with different carrier concentrations: the first region (source/drain) has high carrier concentration for high on-current, while the second region (channel) has low carrier concentration for low off-current. This spatial segmentation allows simultaneous optimization of both on-current and off-current characteristics.
Solution Approach 2:
The carrier concentration is locally optimized in each region: high in the source/drain regions for power delivery, low in the channel region for energy conservation. This local quality differentiation enables the transistor to achieve high on/off current ratio while maintaining excellent field effect mobility.
Data Source
Figure 1
Figure 2A~2B
Figure 3
AI summary
A transistor in an embodiment includes an oxide semiconductor layer (112) on a substrate (102), the oxide semiconductor layer (112) including a first region (112-1) and a second region (112-2), a first gate electrode (116) including a region overlapping the oxide semiconductor layer (112), the first gate electrode (116) being arranged on a surface of the oxide semiconductor layer (112) opposite to the substrate (102), a first insulating layer (114) between the first gate electrode (116) and the oxide semiconductor layer (112), and a first oxide conductive layer (108a) and a second oxide conductive layer (108b) between the oxide semiconductor layer (112) and the substrate (102), the first oxide conductive layer (108a) and the second oxide conductive layer (108b) each including a region in contact with the oxide semiconductor layer (112).