Stacked Oxide Semiconductor Structure for Low Off-State Current
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Solution Overview
Problem
Oxygen vacancies and impurity entry in oxide semiconductor layers of transistors lead to increased off-state current and variation in threshold voltage, reducing the reliability of semiconductor devices.
Innovation Solution
A semiconductor device with a stacked oxide semiconductor structure, where a second oxide semiconductor layer with higher indium content forms a carrier path, and barrier layers prevent impurity entry, along with excess oxygen in insulating layers to fill vacancies and reduce defects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If an oxide semiconductor layer is used as a channel formation region, then the transistor can be formed at relatively low temperature and overlap with other transistors, but oxygen vacancies and impurity entry cause increased off-state current and threshold voltage variation
Solution Approach 1:
The oxide semiconductor layer is divided into multiple layers with different compositions and structures. The first oxide semiconductor layer has lower indium content and serves as a barrier layer, while the second oxide semiconductor layer has higher indium content and serves as the carrier path, resolving the contradiction by separating the functions of impurity blocking and carrier transport.
Solution Approach 2:
Different regions of the oxide semiconductor structure are given different local properties. The first oxide semiconductor layer has lower indium content (higher barrier height) to prevent impurity entry, while the second oxide semiconductor layer has higher indium content (lower barrier height) to facilitate carrier transport, achieving both reliability and low-temperature formation.
2Speed
If the proportion of indium in the oxide semiconductor layer is increased, then carrier mobility is improved, but the layer becomes more susceptible to oxygen vacancy and impurity effects
Solution Approach 1:
The oxide semiconductor structure is segmented into two layers with different indium proportions. The second layer has higher indium content for high carrier mobility, while the first layer has lower indium content for high resistance to oxygen vacancy and impurity, thus resolving the contradiction through functional separation.
Solution Approach 2:
The first oxide semiconductor layer acts as an intermediary barrier layer between the source/drain electrodes and the second oxide semiconductor layer. It protects the high-indium-content layer from oxygen vacancy and impurity effects while allowing carriers to pass through, thus enabling high mobility without susceptibility to degradation.
3Device complexity
If a single-layer oxide semiconductor structure is used, then the device structure is simple, but impurities can easily enter and cause electrical characteristic shifts
Solution Approach 1:
The oxide semiconductor structure is divided into two layers: the first layer serves as a barrier layer to prevent impurity entry, while the second layer serves as the channel formation layer. This segmentation provides impurity protection while maintaining relatively simple device structure.
Solution Approach 2:
The oxide semiconductor device uses a composite structure of two oxide semiconductor layers with different compositions. The first layer (lower indium content) and second layer (higher indium content) are combined to create a structure that resists impurity entry while maintaining good electrical characteristics.
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
The solution results in stable electrical characteristics and improved reliability of semiconductor devices by reducing off-state current and threshold voltage variation.
Implementation Method 1
the proportion of indium in the second oxide semiconductor layer is higher than that in each of the first oxide semiconductor layer and the third oxide semiconductor layer, the second oxide semiconductor layer has high carrier mobility and serves as a carrier path
Implementation Method 2
excess oxygen in insulating layers to fill vacancies and reduce defects
Implementation Method 3
barrier layers prevent impurity entry
Data Source
AI summary
To provide a highly reliable semiconductor device exhibiting stable electrical characteristics. To fabricate a highly reliable semiconductor device. Included are an oxide semiconductor stack in which a first oxide semiconductor layer, a second oxide semiconductor layer, and a third oxide semiconductor layer are stacked, a source and a drain electrode layers contacting the oxide semiconductor stack, a gate electrode layer overlapping with the oxide semiconductor layer with a gate insulating layer provided therebetween, and a first and a second oxide insulating layers between which the oxide semiconductor stack is sandwiched. The first to the third oxide semiconductor layers each contain indium, gallium, and zinc. The proportion of indium in the second oxide semiconductor layer is higher than that in each of the first and the third oxide semiconductor layers. The first oxide semiconductor layer is amorphous. The second and the third oxide semiconductor layers each have a crystalline structure.