Oxide Semiconductor Transistor Structure for Impurity Barrier Control
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Solution Overview
Problem
In semiconductor devices with oxide semiconductor transistors, impurities such as hydrogen and silicon can generate carriers, leading to increased off-state current and variations in threshold voltage, reducing the reliability of the semiconductor device.
Innovation Solution
A semiconductor device structure is implemented with a first oxide layer, an oxide semiconductor layer, source and drain electrode layers, a second oxide layer, a gate insulating layer, and a gate electrode layer, where the first and second oxide layers do not contain impurity elements like silicon, reducing interface scattering and trap levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If oxide semiconductor layer is used as channel formation region, then transistor can be formed with low off-state current, but impurity entry (hydrogen, silicon) generates carriers and increases off-state current
Solution Approach 1:
An oxide insulating layer is introduced as an intermediary barrier between the oxide semiconductor layer and the surrounding environment. This oxide insulating layer contains oxygen in excess of stoichiometric composition and serves as a protective mediator that prevents impurity entry (hydrogen, silicon) into the oxide semiconductor layer while maintaining the low off-state current characteristic of oxide semiconductor transistors.
Solution Approach 2:
The oxide insulating layer is formed with oxygen in excess of stoichiometric composition before the transistor operation. This preliminary oxygen enrichment creates a protective barrier that proactively prevents impurity entry into the oxide semiconductor layer, thereby maintaining reliable low off-state current characteristics from the outset.
2Reliability
If oxygen is supplied to fill oxygen vacancies, then threshold voltage variations are reduced, but excessive oxygen in silicon oxide film must be managed
Solution Approach 1:
The patent extracts and utilizes the excessive oxygen from the oxide insulating layer (which contains oxygen in excess of stoichiometric composition) and directs it to fill oxygen vacancies in the oxide semiconductor layer. This takes the potentially problematic excessive oxygen and converts it into a beneficial resource for improving threshold voltage stability.
Solution Approach 2:
The oxide insulating layer acts as an intermediary oxygen reservoir. It contains oxygen in excess of stoichiometric composition and serves as a controlled source that supplies oxygen to the oxide semiconductor layer through heat treatment, thereby filling oxygen vacancies and stabilizing threshold voltage without uncontrolled oxygen release.
3Reliability
If interface scattering is reduced by using pure oxide layers, then field-effect mobility increases, but manufacturing complexity increases due to additional oxide layers
Solution Approach 1:
The oxide insulating layer performs multiple functions simultaneously: it serves as a protective barrier against impurity entry, as an oxygen source for filling vacancies, and as an interface layer that reduces scattering. This multi-functionality justifies the additional layer by consolidating multiple protective and performance-enhancing roles into a single component.
Data Source
AI summary
The on-state characteristics of a transistor are improved and thus, a semiconductor device capable of high-speed response and high-speed operation is provided. A highly reliable semiconductor device showing stable electric characteristics is made. The semiconductor device includes a transistor including a first oxide layer; an oxide semiconductor layer over the first oxide layer; a source electrode layer and a drain electrode layer in contact with the oxide semiconductor layer; a second oxide layer over the oxide semiconductor layer; a gate insulating layer over the second oxide layer; and a gate electrode layer over the gate insulating layer. An end portion of the second oxide layer and an end portion of the gate insulating layer overlap with the source electrode layer and the drain electrode layer.