Buried Channel Oxide Semiconductor Transistor Structure
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Solution Overview
Problem
The electrical characteristics of oxide semiconductor transistors are degraded due to interface scattering and trap levels at the interface between the oxide semiconductor layer and the insulating layer, leading to reduced field-effect mobility and reliability.
Innovation Solution
A bottom-gate transistor structure is implemented with an oxide semiconductor stack comprising a first and third oxide semiconductor layer with lower carrier densities, sandwiching a second oxide semiconductor layer with n-type conductivity, which acts as a buried channel, reducing interface scattering and trap level influence, and stabilizing the interface.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the oxide semiconductor layer is placed in direct contact with the insulating layer, then the device structure is simple, but interface scattering and trap levels degrade field-effect mobility
Solution Approach 1:
The oxide semiconductor layer is divided into multiple layers: a first oxide semiconductor layer in contact with the insulating layer, a second oxide semiconductor layer forming the channel, and a third oxide semiconductor layer on top. This segmentation separates the channel formation region from direct contact with the insulating layer, reducing interface scattering while maintaining structural organization.
Solution Approach 2:
The first and third oxide semiconductor layers act as intermediary buffer layers between the insulating layer and the channel-forming second oxide semiconductor layer. These buffer layers stabilize the interface and prevent direct contact between the channel and insulating layer, thereby reducing interface scattering and trap level effects.
2Reliability
If the oxide semiconductor layer is placed in direct contact with the silicon oxide film, then the manufacturing process is simple, but silicon impurity mixes into the channel causing degradation
Solution Approach 1:
The first oxide semiconductor layer serves as an intermediary buffer between the silicon oxide insulating layer and the channel-forming second oxide semiconductor layer. This buffer layer prevents silicon atoms from the insulating layer from diffusing into the channel, thereby maintaining channel purity and stable electrical characteristics.
Solution Approach 2:
The oxide semiconductor structure is segmented into three distinct layers with different functions. The first layer contacts the insulating layer and acts as a diffusion barrier, the second layer forms the channel, and the third layer provides additional protection. This segmentation effectively blocks impurity mixing while maintaining structural integrity.
3Reliability
If interface states exist at the oxide semiconductor-insulating layer interface, then the device can be manufactured with standard processes, but trap levels cause changes in electrical characteristics
Solution Approach 1:
The first and third oxide semiconductor layers function as buffer layers that stabilize the interface between the insulating layer and the channel. These buffer layers reduce the impact of interface states and trap levels on the channel, preventing threshold voltage shifts and other electrical characteristic changes while maintaining manufacturability.
Solution Approach 2:
By dividing the oxide semiconductor into three layers, the interface problems are isolated to the buffer layers rather than affecting the channel directly. The second oxide semiconductor layer forming the channel is protected from interface states, ensuring stable electrical characteristics.
Data Source
AI summary
High field-effect mobility is provided for a transistor including an oxide semiconductor. Further, a highly reliable semiconductor device including the transistor is provided. In a bottom-gate transistor including an oxide semiconductor layer, an oxide semiconductor layer functioning as a current path (channel) of the transistor is sandwiched between oxide semiconductor layers having lower carrier densities than the oxide semiconductor layer. In such a structure, the channel is formed away from the interface of the oxide semiconductor stacked layer with an insulating layer in contact with the oxide semiconductor stacked layer, i.e., a buried channel is formed.